Rayzo
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Maximizing Muscle Growth Pathways
Spoiler: Contents Table
AR Genomic pathway
Non-Genomic pathway
Transcriptomic AR Modulation & CPT-1 Transport
Estrogen Receptor (ERα) Autocrine Loop
Progesterone (PgR) / Dopamine (D2) Axis
GH / IGF-1 & PI3K / Akt / mTORC1 Axis
Glucocorticoid Receptor (GR) Antagonism
TGF-β / Myostatin Suppression Loop
GLP-1 Receptor Cascade
cGMP / PKG Cascade
AT1 / eNOS Blockade
HIF-1α / VEGF Angiogenesis Pathway
PPARδ / PGC-1α Axis
Thyroid Hormone (TR) Axis
Introduction
Spoiler: Introduction
Disclaimer: This thread discusses experimental and theoretical topics. The content is primarily based on individual studies, mechanistic reasoning, and preliminary evidence. For some of these compounds, animal or in vitro studies is all the information currently available. I am not a doctor, and definitely not your doctor. Nothing in this thread should be taken as medical advice. The decision to use any of the compounds listed is entirely up to the user's discretion and risk. Proceed accordingly.
WARNING:
THIS IS NOT A “UNIVERSAL” CYCLE. THE PURPOSE OF THIS THREAD IS ONLY TO SHOWCASE THE MOST OPTIMAL WAY POSSIBLE TO INDIVIDUALLY HIT AN INDIVIDUAL GROWTH PATHWAY.
The contents of this thread are rapidly evolving topics, any inaccuracies regarding mechanisms and intracellular cascades will be fixed and updated following new studies or discoveries.
From a mechanism standpoint, a synergistic-multi-layered protocol which targets different pathways for muscle growth is much more superior as it treats muscle growth for what it really is; a multi-layer, multi-pathway endocrinology system.
This is what this thread focuses on, explaining how to theoretically hit every pathway the most “ideal” way possible.
But before diving deeply into the theoretical mechanisms of each of these compounds, it is critical to emphasize that some of them carry significant physiological risks. If a protocol including some of the compounds mentioned was to be created, extensive security measures, bloodwork, and a competent ancillary stack would be mandatory, not optional.
This thread uses an advanced vocabulary, for this reason an appendix with all the technical definitions will be provided at the end of the thread.
Genomic AR Pathway
Spoiler: The AR Genomic
The AR Genomic Pathway
This is the classic cascade most AAS trigger. Trenbolone or Trestolone (MENT) are chosen here due to their insane binding affinity, outstanding intrinsic potency, transcriptional potency, unique behavior and activation of certain AREs, super low IC50, and exceptional bioavailability (also because they have a side effect profile reasonable enough to manage), all ensuring the ARs are fully saturated and occupied with peak efficiency. Now before anyone starts saying anything, yes, substantially more potent alternatives such as Dimethynortestosterone (Cheque drops), Methyltrienolone (M-Tren), and Dimethyltrienolone (RU2420) exist, but let's be honest, very few or none are willing to take compounds like those (especially the last one).
Before anything, AI sucks at making diagrams even when perfect instructions are given so many corrections were performed, there was 1 that couldn't be fixed though. In step 4 the diagram shows the AR forming a homodimer (pairing up) in the cytoplasm before moving through the nuclear pore, here is where the technical nuance comes, because while this is the classic textbook model, recent advanced live-cell imaging suggests that the AR actually translocates into the nucleus as a monomer and then dimerizes once it reaches the DNA and not before.
Trenbolone
Also known as S,13S,14S,17S)-17-Hydroxy-13-methyl-2,6,7,8,14,15,16,17-octahydro-1H-cyclopenta[a]phenanthren-3-one (Long ass IUPAC i know) is a 19-nortestosterone derivative (Nandrolone derivative), to put it as simple as possible, a Testosterone molecule where the angular C19 methyl group present in testosterone has been completely removed, what does this achieve? It increases the AR binding affinity dramatically, additionally; Trenbolone’s unique properties stem from its chemical structure, specifically from three double bonds at the positions C4-C5, C9-C10, and C11-C12 of its structure, this spatial arrangement configuration achieves three critical pharmacological end points which are what make Trenbolone such a unique compounds
Image showcasing the molecular structure of the Trenbolone ligand
1: It fully (or almost) avoids interactions with the cytochrome P450 aromatase enzyme complex (effectively blocking all or almost all conversion to Estradiol (E₂) through aromatase enzyme metabolism).
2: It also avoids 5a-reduction because the 5a-reductase enzyme relies on a very specific "3D shape" to bind onto the A-ring which is simply not possible to do so because of the shape of the ligand, as result the enzyme simply cannot physically recognize or properly bind to the highly flattened A-ring to reduce that C4-C5 bond,
3: Finally the ligand shows an outstandingly low binding affinity to SHBG.
All of these properties working as a whole make tren such a special compound without even mentioning its insane binding affinity for the AR both in vivo and in vitro. Trenbolone also possesses very interesting GR antagonism properties (which will be explained with a luxury of details in the "Anti-Catabolic Compounds" section) while it simultaneously shows an outstanding capacity to recruit satellite cell activation and Insulin-like Growth Factor 1 (IGF-1) expression as it causes a local increase in intramuscular IGF-1 and simultaneously upregulates the sensitivity of satellite cells (muscle stem cells). These properties facilitate myonuclear addition, increasing the long-term ceiling for protein synthesis and tissue remodeling.
Trestolone
Also known as (7α,17β)-17-Hydroxy-7-methylestr-4-en-3-one shares a lot in common with Trenbolone as both are part of the same family of derivatives (19-nortestoreone derivatives). In contrast with Trenbolone, Trestolone’s properties also stem from a chemical modification, specifically the addition of a bulky methyl group at the 7th carbon position on the alpha face (the 7a-methyl alteration) of its structure.
This specific spatial arrangement achieves two critically desired pharmacokinetic properties
1: It creates immense steric hindrance (steric hindrance is the name of the interaction when a bulky atom or groups of atoms in a molecule get in the way of other molecules trying to react with it, basically, a physical block) that functionally eliminates interaction with Sex Hormone-Binding Globulin (SHBG).
2: It also simultaneously entirely avoids (or almost) 5a-reductase enzyme metabolism because the enzyme must physically approach the alpha face of the A and B rings to reduce the C4-C5 bond, but this is not possible because it’s geometrically blocked by the protruding methyl group.
It also shares with Trenbolone a similar binding affinity for the AR both in vivo and in vitro, however, in vivo Trestolone experiences some pharmacokinetic issues regarding metabolic clearance and target-site competition because it does not avoid the aromatase enzyme metabolism conversion to E₂.
Simultaneously, this is also the reason Trestolone can self-sustain its own anabolic environment via the Estrogen Receptor Alpha (ERα) loop due to its localized conversion to 7a-methyl-estradiol, which is required to directly upregulate the transcription of the AR itself, consequently continuously increasing nuclear AR density over time facilitating the expansion of the structural capacity for genomic transcription and avoiding the receptor-saturation halt and stunted growth factor expression that heavily affects estrogen deprived cycles. Additionally, Trestolone also possesses extreme tissue selectivity, which allows it to concentrate its immense myogenic potency directly on skeletal muscle without significantly intensifying its effects on non-skeletal muscle tissue, minimizing the risk of experiencing the undesired commonly experienced androgenic side effects from other AAS which are less selective.
Comprehensive Receptor Binding & Potency Data
Non-Genomic AR Pathway
Spoiler: Non-Genomic AR Pathway
The Non-genomic AR Pathway
Unlike the genomic pathway, the non-genomic pathway avoids the slow process of the ligand-AR complex translocating to the nucleus to bind to Androgen Response Elements (AREs) on DNA (which is by the way, quite a slow process, taking around 45+ minutes to initiate transcription and hours to translate folded proteins) by following a completely different sequence of steps which occurs much faster as it’s a transcription-independent cascades that occurs within seconds to minutes, which is the main advantage to leverage.
The Step-by-Step Mechanism:
Instead of waiting for the whole DNA transcription process to occur, this process immediately forces the cytosol to translate existing mRNA into protein, while driving strong cytoskeletal structural changes that pull water and nutrients into the cell. This is why heavily modified super-potent oral AAS like Anadrol exhibit poor classical AR binding affinity but induce immense hypertrophy because they exploit these rapid cascades.
Oxymetholone (also known as 17β-Hydroxy-2-(hydroxymethylene)-17α-methyl-5α-androstan-3-one) (Or commonly known as "Anadrol") is a very potent modified oral AAS derived from dihydrotestosterone (DHT). To put it as simply as possible, it is a DHT molecule that has undergone two critical structural modifications 1. The addition of a methyl group at the 17α position and 2. The attachment of a 2-hydroxymethylene group on the A-ring.
Important disclaimer: Despite the fact Oxymetholone is a DHT derivative, clinical literature suggests the added 2-hydroxymethylene group which significantly alters the ligand's shape might enable it to directly agonize the estrogen receptor (ER) or induce progestogenic activity, causing significant estrogenic effects which are completely independent of aromatase metabolism itself.
What does this achieve? It grants Oxymetholone high oral bioavailability while simultaneously altering both its receptor binding kinetics and metabolic outcome. Now, this structural modifications achieve three critical pharmacological endpoints:
1: It fully avoids interacting with both the 5α-reductase enzyme and with the cytochrome P450 aromatase enzyme complex due to the fact its already 5α-reduced.
(Chemical explanation: This properties are due to its A-ring lacking the C4-C5 double bond required for aromatase metabolism, meaning there is zero conversion to E₂ and it completely avoids 5α-reduction because the 5α-reductase enzyme has no double bond to reduce on the A-ring.)
2: The ligand shows an extraordinarily low binding affinity for both SHBG and the AR. The 17α-methyl and 2-hydroxymethylene groups severely lowers SHBG binding, resulting in a massive free (unbound) fraction of the hormone in circulation.
3.Its 17α-alkylation acts as a steric shield, preventing oxidation by the 17β-hydroxysteroid dehydrogenase enzyme in the liver, making it survive hepatic metabolism and work orally. This also makes it induce liver toxicity to some degree.
All of these properties combined make Oxymetholone such an interesting and unique compound because it induces an extreme muscle accretion which paradoxically occurs despite of its poor AR binding affinity in vitro (which is significantly lower than the one of testosterone or other AAS). This can further be used to demonstrate that its primary mechanism of action relies heavily on the previously described non-genomic pathway rather than the conventional AR genomic pathway. To continue expanding on its extraordinary pharmacokinetic properties, Oxymetholone also possesses the capacity to strongly stimulate erythropoiesis by potently upregulating the synthesis of erythropoietin (EPO) in the kidneys and also directly increasing the responsiveness of erythroid progenitor cells increasing RBC.
To conclude, Oxymetholone is chosen here due to two factors
1: compared to methyldrostanolone (Superdrol) it is much safer on the liver and has more studies and long term data,
2: second is; as previously explained, it's main mechanism of action is not the classic genomic pathway but rather the non genomic pathway as it potently targets surface-level membrane receptors (mAR and ZIP9) which makes it the optimal choice to agonize this intracellular cascade.
Further expanding into its mechanisms, when the rapid interaction with the surface-level membrane receptors occurs, it immediately triggers an intracellular Ca²⁺ influx and phosphorylates the Src/MAPK/ERK cascade. Now this can become in a way a double edged sword because while this cascade is the exact mechanism responsible for rapid cytoskeletal remodeling and massive intracellular swelling in skeletal muscle, mechanistic logic suggests it can simultaneously theoretically degrade skin quality as chronic activation of the MAPK/ERK pathway causes Matrix Metalloproteinase (MMP) upregulation, MMPs being enzymes that downregulate the production of collagen and elastin on the dermis.
Expanding the Cellular binding
Spoiler: Expanding the Cellular binding
To expand the potency of AAS ligands, L-Carnitine (specifically administered via a highly bioavailable route to bypass first-pass hepatic degradation) is deployed as a structural amplifier because it facilitates the mitigation of receptor saturation and expands transcription efficiency which is optimal as the ultimate dead end of genomic signaling is the finite density of ARs inside skeletal muscle tissue.
Clinical literature (e.g., Kraemer et al.) shows that L-Carnitine upregulated AR density in skeletal muscle cells following resistance exercise. Mechanistically, it acts as a selective transcriptomic modulator, increasing the baseline population of available nuclear receptor proteins. By expanding the structural binding pool, it allows a higher volume of circulating Androgen ligands to bind to the expanded AR pool amplifying total muscle protein synthesis (MPS) without necessarily requiring an increase in androgen dosages.
Mitochondrial Acyl-CoA Transport: Beyond the receptor regulation, L-Carnitine serves as a relevant facilitator (substrate) for Carnitine Palmitoyltransferase-1 (CPT-1) because it facilitates the translation of long-chain fatty acids to the inner mitochondrial membrane into the matrix for β-oxidation, this becomes a great tool as heavy androgen transcription and insulin translation place an extreme energy (ATP) demand on the cell, optimizing mitochondrial substrate oxidation grants a needed metabolic buffer, which helps to sustain the high-energy environment required to keep translation steady and active.
Despite all of this, L-Carnitine is theoretically merely a support compound, nothing else.
Cellular Amplifiers (GH & Insulin)
Spoiler: Cellular Amplifiers (GH & Insulin)
Cellular Amplifiers (GH & Insulin)
To unlock another pathway, we will analyze the GH/IGF-1 Axis, one of the main limiting factors of growth is that skeletal muscle fibers operate under a strict myonuclear (or single) capacity, this means a single nucleus can only manage a limited amount of cytoplasm. Now, despite the fact that AAS accelerate muscle protein synthesis, they are relatively less efficient at adding new myonuclei via satellite cell fusion. This is where GH comes into play.
What does Growth Hormone (GH) do?: GH stimulates both hepatic and local production of IGF-1 which makes it a very useful tool, it also possesses another quite interesting mechanism because when mechanical stress or hormonal signaling surges, the IGF-1 gene splices into different isoforms: IGF-1Ec and IGF-1Ea
Their functions:
IGF-1Ec (Mechano-Growth Factor or "MGF") acts locally as an autocrine/paracrine pulse specifically activating dormant satellite cells (muscle stem cells) and stimulating their proliferation, consequently forcing them to bind with damaged muscle fibers and donate their nuclei.
IGF-1Ea (Systemic) isoform follows up MGF by promoting the differentiation of these new cells by permanently expanding the myonuclear pool. Consequently this action increases the overall structural capacity of the muscle fiber to sustain growth without stretching the myonuclear domain beyond its limit.
Its widely known insulin is the most potent anti-catabolic and nutrient-partitioning compound available, and as mentioned before, GH use becomes quite redundant without the use of insulin.
Why do we need insulin?: The simple explanation is that exogenous GH via IGF-1 triggers satellite cell fusion to add new myonuclei to the muscle fiber expanding the total nuclear pool to sustain growth without exceeding the myonuclear domain, now, the issue is this expanded nuclear pool remains translationally very limited (Almost inactive) without the cellular energy required to convert its transcribed mRNA into folded proteins, which insulin solves by accelerating glucose uptake, consequently generating the massive ATP flux required for ribosomal translation.
How does insulin work?: When insulin binds to its extracellular receptor (the tyrosine kinase) it triggers a process known as autophosphorylation (which is when the protein kinase adds a phosphate group to itself), as a result activating Insulin Receptor Substrate 1 (IRS-1), consequently this interaction triggers the next downstream cascade: IRS-1 → PI3K → Akt → mTORC1 which translocates the GLUT4 transporters to the membrane, simultaneously forcing an immediate intracellular influx of glucose and upregulates distinct transporters (such as System A and LAT1) to drive the uptake of amino acids. As a result of this whole process it provides the energy (ATP) and materials required to execute the protein synthesis instructions previously transcribed by the targeted AR genomic pathway.
Insulin & AMPK: To achieve ideal anabolism it requires the unrestricted activation of mTORC1, the issue is massive protein synthesis is very energy consuming and rapidly consumes cellular ATP. This becomes a very big problem because when ATP decreases and AMP levels increase, the cell's primary energy sensor AMPK (5' AMP-activated protein kinase) gets strongly activated by this interaction which then directly phosphorylates and activates TSC2 (which is a tumor suppressor complex) strongly shutting down mTORC1 to preserve energy. To solve this energy crisis and prevent AMPK activation, using insulin is mandatory to shut down this inhibitory mechanism because insulin-activated Akt directly phosphorylates and inhibits TSC2 effectively neutralizing AMPK’s inhibitory action on mTORC1. This synergistic combination of exogenous GH and Insulin keeps the mTORC1 pathway open allowing for sustained protein synthesis while simultaneously maintaining cellular energy homeostasis.
Why Tresiba?: Insulin Degludec (or also known as "Tresiba") in contrast to her other cousins (like Humalog or Novolog) it’s not a rapid-acting insulin. Tresiba is an ultra-long-acting basal insulin that lasts for at least 42 hours in the body; it achieves this pharmacokinetic outcome because it forms multi-hexamers in the subcutaneous tissue, rather than to fix insulin resistance itself, it trades pulsatile sensitivity for a stable and predictable outcome avoiding the chaotic hypoglycemic crashes triggered by rapid-acting insulins like Humalog or Novolog.
This synergistic combination allows GH to potently expand the myonuclear domain while Insulin (Tresiba) simultaneously helps attenuate the consequent blood glucose spike, manages the ATP demand, and prevents the activation of AMPK/TSC2 inhibitory pathway.
Anti-Catabolism
Spoiler: Anti-Catabolism
Spoiler: HPA Axis
Spoiler: GR Antagonism via Trenbolone
Spoiler: GR Antagonism via Mifepristone or Relacorilant
Spoiler: Myostatin Inhibition (TGF-β Superfamily)
Spoiler: The β₂-Adrenergic-Cascade
Spoiler: The GLP-1 Receptor Cascade
Spoiler: The cGMP / PKG Cascade
Infrastructure & Environmental Support
Spoiler: Infrastructure & Environmental Support
Spoiler: The Estrogen Fallacy
Spoiler: eNOS and PPARδ Pathway
Spoiler: The Progestogenic & Pituitary Axis
Spoiler: The Thyroid Hormone Axis (T3/T4)
Spoiler: VGEF Pathway
Conclusion
Spoiler: Conclusion
This thread illustrates how to theoretically maximize and target individual cellular pathways, showing that a multi-pathway saturation is tremendously superior to the strategies seen on Bodybuilding and Looksmaxxing forums. However, this thread only serves as a conceptual model of biological mechanisms rather than the recipe to create an universal stack.
This thread remains strictly a theoretical framework, the combined in vivo interactions of most (if not to say almost all) of these compounds is entirely untested. The individual pathways analyzed and covered on this thread are based in some established molecular biology and isolated individual clinical literature for the compounds that have this kind of data available. However, not all of them do, some have very limited human data or very limited data overall.
Further investigation is required to validate these concepts beyond the theoretical level.
References & Appendix
Spoiler: References
Aguirre-Portolés, C., Payne, R., Trautz, A., Foskett, J. K., Natale, C. A., Seykora, J. T., & Ridky, T. W. (2021). ZIP9 is a druggable determinant of sex differences in melanoma. Cancer Research, 81(23), 5991–6003. https://doi.org/10.1158/0008-5472.can-21-0982
Bond, P., Smit, D. L., & de Ronde, W. (2022). Anabolic–androgenic steroids: How do they work and what are the risks? Frontiers in Endocrinology, 13, 1059473. https://doi.org/10.3389/fendo.2022.1059473
Brodde, O. E., Brinkmann, M., Schemuth, R., O'Hara, N., & Daul, A. (1985). Terbutaline-induced desensitization of human lymphocyte beta 2-adrenoceptors. Accelerated restoration of beta-adrenoceptor responsiveness by prednisone and ketotifen. Journal of Clinical Investigation, 76, 1096-1101.
https://doi.org/10.1172/jci112063
Cormerais, Y., Lapp, S. C., Kalafut, K. C., et al. (2024). AKT-mediated phosphorylation of TSC2 controls stimulus- and tissue-specific mTORC1 signaling and organ growth. bioRxiv. https://doi.org/10.1101/2024.09.23.614519
Custodio, J. M., Donaldson, K. M., & Hunt, H. J. (2020). An in vitro and in vivo evaluation of the effect of relacorilant on the activity of cytochrome P450 drug metabolizing enzymes. The Journal of Clinical Pharmacology, 61(2), 244–253. https://doi.org/10.1002/jcph.1731
Galbraith, H., & Chalmers, I. M. (1986). The effect of manipulating growth in sheep by diet or anabolic agents on plasma cortisol and muscle glucocorticoid receptors. British Journal of Nutrition, 56(1), 109–118. https://doi.org/10.1079/bjn19860107
Kanno, Y., Ota, R., Someya, K., Kusakabe, T., Kato, K., & Inouye, Y. (2013). Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biological and Pharmaceutical Bulletin, 36(9), 1460–1465. https://doi.org/10.1248/bpb.b13-00231
Karantanos, T., Evans, C. P., Lara, P. N., Jr, Ao, A. Y., & Ghosh, P. M. (2013). Androgen receptor-mediated non-genomic regulation of prostate cancer cell proliferation. Translational Andrology and Urology, 2(3), 147–157.
Kraemer, W. J., Volek, J. S., French, D. N., Rubin, M. R., Sharman, M. J., Gómez, A. L., Ratamess, N. A., Newton, R. U., Jemiolo, B., Craig, B. W., & Häkkinen, K. (2003). The effects of L-carnitine L-tartrate supplementation on hormonal responses to resistance exercise and recovery. The Journal of Strength and Conditioning Research, 17(3), 455–462. https://doi.org/10.1519/1533-4287(2003)017<0455:teolls>2.0.co;2
Koshino, T., Agrawal, D. K., Townley, T. A., & Townley, R. G. (1988). Ketotifen prevents terbutaline-induced down-regulation of beta-adrenoceptors in Guinea pig lung. Biochemical and Biophysical Research Communications, 152, 1221-1227. https://doi.org/10.1016/s0006-291x(88)80415-7
Leung, J. K., & Sadar, M. D. (2017). Non-genomic actions of the androgen receptor in prostate cancer. Frontiers in Endocrinology, 8, 2.
Malviya, V. N., Bulldan, A., Wende, R. C., et al. (2021). The effects of tetrapeptides designed to fit the androgen binding site of ZIP9 on myogenic and osteogenic cells. Biology, 11(1), 19. https://doi.org/10.3390/biology11010019
Masi, M., Racchi, M., Travelli, C., Corsini, E., & Buoso, E. (2021). Molecular characterization of membrane steroid receptors in hormone-sensitive cancers. Cells, 10(11), 2999. https://doi.org/10.3390/cells10112999
Mauvais-Jarvis, F., Lange, C. A., & Levin, E. R. (2021). Membrane-initiated estrogen, androgen, and progesterone receptor signaling in health and disease. Endocrine Reviews, 43(4), 720–742. https://doi.org/10.1210/endrev/bnab041
McKoy, G., Ashley, W., Mander, J., Yang, S. Y., Williams, N., Russell, B., & Goldspink, G. (1999). Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation. The Journal of Physiology, 516(2), 583–592. https://doi.org/10.1111/j.1469-7793.1999.0583u.x
Miyazaki, M., McCarthy, J. J., Fedele, M. J., & Esser, K. A. (2011). Early activation of mTORC1 signalling in response to mechanical overload is independent of phosphoinositide 3‐kinase/Akt signalling. The Journal of Physiology, 589(7), 1831–1846. https://doi.org/10.1113/jphysiol.2011.205658
Parr, M. K., & Mc Laughlin, A. M. (2021). Signalling cascade on non-genomic action of anabolic androgenic steroids. ResearchGate.
Pillerová, M., Borbélyová, V., Hodosy, J., Riljak, V., Renczés, E., Frick, K. M., & Tóthová, L. (2021). On the role of sex steroids in biological functions by classical and non-classical pathways: An update. Frontiers in Neuroendocrinology, 62, 100926. https://doi.org/10.1016/j.yfrne.2021.100926
Stefan, M., Sharp, M., Gheith, R., et al. (2021). L-carnitine tartrate supplementation for 5 weeks improves exercise recovery in men and women: A randomized, double-blind, placebo-controlled trial. Nutrients, 13(10), 3432. https://doi.org/10.3390/nu13103432
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Thomas, P., Pang, Y., Dong, J., Berg, A. H., & Dushay, J. (2014). Identification and characterization of membrane androgen receptors in the ZIP9 zinc transporter subfamily. Endocrinology, 155(11), 4250–4265.
Viho, E. M., Kroon, J., Feelders, R. A., et al. (2022). Peripheral glucocorticoid receptor antagonism by relacorilant with modest HPA axis disinhibition. Journal of Endocrinology, 255(1). https://doi.org/10.1530/joe-22-0263
Wang, R., Zhong, Y., Du, Q., Zhao, C., Wang, Y., & Pan, J. (2024). YK11 promotes osteogenic differentiation of BMSCs and repair of bone defects. Journal of Molecular Endocrinology, 74(2). https://doi.org/10.1530/jme-24-0073
Appendix:
Abreviations:
11ẞHSD2: 11ẞ-hydroxysteroid dehydrogenase type 2
AAS: Anabolic Androgenic Steroids
ACTH: Adrenocorticotropic hormone
AI: Aromatase Inhibitor
AMP: Adenosine monophosphate
AMPK: 5' AMP-Activated Protein Kinase
AR: Androgen Receptor
ARE: Androgen Response Element
ARBS: Angiotensin II Receptor Blockers
ATP: Adenosine triphosphate
cAMP: Cyclic adenosine monophosphate
cGMP: Cyclic guanosine monophosphate
CPT-1: Carnitine Palmitoyltransferase-1
D2: Dopamine Receptor (specifically the D2 subtype)
DHT: Dihydrotestosterone
E2: Estradiol
eNOS: Endothelial Nitric Oxide Synthase
ERa: Estrogen Receptor Alpha
GAP: GTPase-activating protein
GCR/GR: Glucocorticoid Receptor
GH: Growth Hormone
GLP-1: Glucagon-Like Peptide-1
GLUT4: Glucose Transporter Type 4
HIF-1α: Hypoxia-Inducible Factor 1-alpha
HPA: Hypothalamic-Pituitary-Adrenal (axis)
HSP: Heat Shock Proteins
IC50: Half-Maximal Inhibitory Concentration
IGF-1: Insulin-like Growth Factor 1
IRS-1: Insulin Receptor Substrate 1
Kd: Dissociation Constant
Ki: Inhibition Constant
LAT1: L-type amino acid transporter 1
LBD: Ligand-Binding Domain
LVH: Left Ventricular Hypertrophy
mAR: Membrane Androgen Receptor
MAPK: Mitogen-activated protein kinase
MENT: Methyl-nortestosterone (Trestolone)
MGF: Mechano-Growth Factor (also known as IGF-1Ec)
MMP: Matrix Metalloproteinase
MPB: Muscle Protein Breakdown
MPS: Muscle Protein Synthesis
MR: Mineralocorticoid Receptor
mTORC1: Mechanistic Target of Rapamycin Complex 1
PDE5I: PDE5 inhibitors
PgR: Progesterone Receptor
PI3K: Phosphoinositide 3-Kinase
PKA: Protein Kinase A
PKG: Protein Kinase G
PPAR: Peroxisome Proliferator-Activated Receptor
RBA: Relative Binding Affinity
SHBG: Sex Hormone-Binding Globulin
SR: Sarcoplasmic Reticulum
T3: Triiodothyronine
T4: Thyroxine
TGF-β: Transforming Growth Factor-beta
TR: Thyroid Hormone Receptor
TSC2: Tuberous Sclerosis Complex 2
VEGF: Vascular Endothelial Growth Factor
Defintions:
Adenylate Cyclase: A membrane-bound enzyme that catalyzes the conversion of ATP into cyclic adenosine monophosphate (cAMP). It serves as the primary effector for Gs-protein-coupled receptors, initiating intracellular signaling cascades.
Akt (Protein Kinase B): A critical cytosolic serine/threonine-specific protein kinase that plays a key role in multiple cellular processes such as glucose metabolism, apoptosis, cell proliferation, and transcription. It acts as the primary downstream effector of PI3K to stimulate mTORC1.
AMPK (5' AMP-Activated Protein Kinase): A central cellular energy sensor enzyme. It is activated by rising AMP levels (indicating cellular energy depletion) and acts to restore ATP homeostasis by shutting down energy-consuming anabolic pathways, such as mTORC1-mediated protein synthesis.
Androgen Receptor (AR): A single nuclear receptor protein encoded by the NR3C4 gene. Structurally composed of an N-terminal transactivation domain, a central DNA-binding domain, and a C-terminal ligand-binding domain (LBD), it acts as a ligand-dependent transcription factor.
Angiogenesis: The physiological process through which new blood vessels form from pre-existing vessels. It is primarily driven by signaling molecules such as VEGF (Vascular Endothelial Growth Factor) in response to localized tissue hypoxia.
Aromatization: The enzymatic biotransformation of specific androgens into corresponding estrogenic substrates via the cytochrome P450 aromatase enzyme complex.
Autocrine / Paracrine Signaling: Forms of cell-to-cell communication. Autocrine signaling occurs when a cell secretes a hormone or chemical messenger that binds to receptors on its own surface. Paracrine signaling occurs when these messengers act on nearby, adjacent cells.
Calpains: A family of calcium-dependent, non-lysosomal cytosolic proteases. Unlike the ubiquitin-proteasome pathway which degrades tagged proteins, calpains actively cleave and break down intact structural muscle proteins (like titin and nebulin) during periods of high intracellular calcium.
E3 Ubiquitin Ligase: A specialized family of enzymes (e.g., MuRF-1, Atrogin-1) that catalyze the attachment of ubiquitin molecules to target proteins. This "tagging" identifies the protein for degradation by the 26S proteasome, a critical step in muscle protein breakdown (MPB).
G-Protein Coupled Receptor (GPCR): A large family of cell surface receptors that detect extracellular signals and activate internal signal transduction pathways. They consist of seven transmembrane helices and are categorized by the type of G-protein (Gs, Gi, Gq) they recruit.
GLUT4 (Glucose Transporter Type 4): An insulin-regulated glucose transporter found primarily in adipose tissues and striated muscle (skeletal and cardiac). Upon activation of the PI3K/Akt pathway, GLUT4 translocates from intracellular vesicles to the plasma membrane to facilitate glucose uptake.
Hypoxia-Inducible Factor 1-alpha (HIF-1alpha): A transcription factor that acts as the master regulator of oxygen homeostasis. Under hypoxic conditions, it avoids degradation and translocates to the nucleus to initiate the expression of genes involved in angiogenesis and metabolic adaptation.
IC50 (Half-Maximal Inhibitory Concentration): A quantitative measure indicating the precise concentration of a ligand required to displace exactly 50% of a reference radiolabeled ligand from a receptor population pool. A lower IC50 indicates exponentially higher binding affinity.
In vivo / In vitro: Latin terms used in research. In vivo refers to biological processes or experiments occurring within a whole, living organism. In vitro refers to processes studied in a controlled, isolated environment outside of a living organism (e.g., in a test tube or petri dish).
Ligand: A specific molecule or atom that can bind to a receptor either irreversibly or reversibly to initiate, modulate, or inhibit a cellular signaling cascade (e.g., Testosterone, Dihydrotestosterone).
Ligand-Binding Domain (LBD): A highly specialized, hydrophobic pocket within a receptor structure designed to exclusively accommodate a compatible ligand, inducing a conformational fold that activates the receptor complex.
Matrix Metalloproteinase (MMP): A group of zinc-dependent endopeptidases capable of degrading extracellular matrix proteins. While vital for tissue remodeling, chronic overexpression (e.g., via sustained MAPK signaling) can lead to the degradation of dermal collagen and elastin.
Myonuclear Domain: The theoretical volume of cytoplasm managed by a single myonucleus. Because muscle fibers are multinucleated, the physical limit of this domain dictates that total fiber hypertrophy is limited by the number of nuclei available; myonuclear addition (via satellite cell fusion) is required to expand this structural ceiling.
Phosphodiesterase-5 (PDE5): An enzyme that catalyzes the hydrolysis of cGMP to 5’-GMP. By inhibiting this enzyme, cGMP levels are sustained, facilitating prolonged smooth muscle relaxation and enhanced vascular perfusion.
PI3K (Phosphoinositide 3-Kinase): A family of enzymes that phosphorylate the 3-position hydroxyl group of the inositol ring of phosphatidylinositol. It is the crucial upstream mediator that translates insulin receptor signaling into the activation of Akt.
PKA (Protein Kinase A): A family of enzymes whose activity is dependent on cellular levels of cAMP. Once activated, PKA phosphorylates specific target proteins to alter their function, playing a critical role in lipid metabolism and anti-catabolic signaling.
PPARbeta/delta (Peroxisome Proliferator-Activated Receptor Delta): A nuclear hormone receptor that acts as a central metabolic regulator, orchestrating lipid oxidation, skeletal muscle fiber type switching, and mitochondrial biogenesis.
Relative Binding Affinity (RBA): A comparative mathematical ratio indicating how tightly a specific synthetic compound binds to a target receptor relative to a reference native hormone (typically Testosterone or Dihydrotestosterone), which is arbitrarily set at a baseline value of 100.
Rheb (Ras homolog enriched in brain): A small GTPase that is a direct activator of mTORC1. Rheb's activity state is controlled by the TSC2 complex: when bound to GTP, Rheb is active and stimulates mTORC1; when TSC2 exerts its GAP activity, Rheb is converted to its inactive GDP-bound state, inhibiting mTORC1.
Sarcoplasmic Reticulum (SR): A specialized type of smooth endoplasmic reticulum found exclusively in myocytes (muscle cells). It acts as a dedicated storage and release sink for calcium ions (Ca2+), regulating muscle contraction.
Satellite Cell: A quiescent, muscle-specific stem cell located between the sarcolemma and the basal lamina of a muscle fiber. Upon activation (e.g., by MGF or mechanical stress), these cells proliferate and fuse with existing muscle fibers to provide additional nuclei.
SHBG (Sex Hormone-Binding Globulin): A glycoprotein that binds to androgens (such as testosterone) and estrogens with high affinity. By sequestering these hormones in the blood, SHBG limits the fraction of "free" (bioavailable) steroid hormone capable of entering the cell to bind with the AR.
TSC2 (Tuberous Sclerosis Complex 2 / Tuberin): A tumor suppressor protein that forms a complex with TSC1. It acts as a GTPase-activating protein (GAP) for Rheb, effectively serving as the "energetic kill-switch" for the mTORC1 pathway.
Spoiler: Contents Table
AR Genomic pathway
Non-Genomic pathway
Transcriptomic AR Modulation & CPT-1 Transport
Estrogen Receptor (ERα) Autocrine Loop
Progesterone (PgR) / Dopamine (D2) Axis
GH / IGF-1 & PI3K / Akt / mTORC1 Axis
Glucocorticoid Receptor (GR) Antagonism
TGF-β / Myostatin Suppression Loop
GLP-1 Receptor Cascade
cGMP / PKG Cascade
AT1 / eNOS Blockade
HIF-1α / VEGF Angiogenesis Pathway
PPARδ / PGC-1α Axis
Thyroid Hormone (TR) Axis
Introduction
Spoiler: Introduction
Disclaimer: This thread discusses experimental and theoretical topics. The content is primarily based on individual studies, mechanistic reasoning, and preliminary evidence. For some of these compounds, animal or in vitro studies is all the information currently available. I am not a doctor, and definitely not your doctor. Nothing in this thread should be taken as medical advice. The decision to use any of the compounds listed is entirely up to the user's discretion and risk. Proceed accordingly.
WARNING:
THIS IS NOT A “UNIVERSAL” CYCLE. THE PURPOSE OF THIS THREAD IS ONLY TO SHOWCASE THE MOST OPTIMAL WAY POSSIBLE TO INDIVIDUALLY HIT AN INDIVIDUAL GROWTH PATHWAY. The contents of this thread are rapidly evolving topics, any inaccuracies regarding mechanisms and intracellular cascades will be fixed and updated following new studies or discoveries.
From a mechanism standpoint, a synergistic-multi-layered protocol which targets different pathways for muscle growth is much more superior as it treats muscle growth for what it really is; a multi-layer, multi-pathway endocrinology system.
This is what this thread focuses on, explaining how to theoretically hit every pathway the most “ideal” way possible.
But before diving deeply into the theoretical mechanisms of each of these compounds, it is critical to emphasize that some of them carry significant physiological risks. If a protocol including some of the compounds mentioned was to be created, extensive security measures, bloodwork, and a competent ancillary stack would be mandatory, not optional.
This thread uses an advanced vocabulary, for this reason an appendix with all the technical definitions will be provided at the end of the thread.
Genomic AR Pathway
Spoiler: The AR Genomic
The AR Genomic Pathway
This is the classic cascade most AAS trigger. Trenbolone or Trestolone (MENT) are chosen here due to their insane binding affinity, outstanding intrinsic potency, transcriptional potency, unique behavior and activation of certain AREs, super low IC50, and exceptional bioavailability (also because they have a side effect profile reasonable enough to manage), all ensuring the ARs are fully saturated and occupied with peak efficiency. Now before anyone starts saying anything, yes, substantially more potent alternatives such as Dimethynortestosterone (Cheque drops), Methyltrienolone (M-Tren), and Dimethyltrienolone (RU2420) exist, but let's be honest, very few or none are willing to take compounds like those (especially the last one).
Before anything, AI sucks at making diagrams even when perfect instructions are given so many corrections were performed, there was 1 that couldn't be fixed though. In step 4 the diagram shows the AR forming a homodimer (pairing up) in the cytoplasm before moving through the nuclear pore, here is where the technical nuance comes, because while this is the classic textbook model, recent advanced live-cell imaging suggests that the AR actually translocates into the nucleus as a monomer and then dimerizes once it reaches the DNA and not before.
Trenbolone
Also known as S,13S,14S,17S)-17-Hydroxy-13-methyl-2,6,7,8,14,15,16,17-octahydro-1H-cyclopenta[a]phenanthren-3-one (Long ass IUPAC i know) is a 19-nortestosterone derivative (Nandrolone derivative), to put it as simple as possible, a Testosterone molecule where the angular C19 methyl group present in testosterone has been completely removed, what does this achieve? It increases the AR binding affinity dramatically, additionally; Trenbolone’s unique properties stem from its chemical structure, specifically from three double bonds at the positions C4-C5, C9-C10, and C11-C12 of its structure, this spatial arrangement configuration achieves three critical pharmacological end points which are what make Trenbolone such a unique compounds
Image showcasing the molecular structure of the Trenbolone ligand
1: It fully (or almost) avoids interactions with the cytochrome P450 aromatase enzyme complex (effectively blocking all or almost all conversion to Estradiol (E₂) through aromatase enzyme metabolism).
2: It also avoids 5a-reduction because the 5a-reductase enzyme relies on a very specific "3D shape" to bind onto the A-ring which is simply not possible to do so because of the shape of the ligand, as result the enzyme simply cannot physically recognize or properly bind to the highly flattened A-ring to reduce that C4-C5 bond,
3: Finally the ligand shows an outstandingly low binding affinity to SHBG.
All of these properties working as a whole make tren such a special compound without even mentioning its insane binding affinity for the AR both in vivo and in vitro. Trenbolone also possesses very interesting GR antagonism properties (which will be explained with a luxury of details in the "Anti-Catabolic Compounds" section) while it simultaneously shows an outstanding capacity to recruit satellite cell activation and Insulin-like Growth Factor 1 (IGF-1) expression as it causes a local increase in intramuscular IGF-1 and simultaneously upregulates the sensitivity of satellite cells (muscle stem cells). These properties facilitate myonuclear addition, increasing the long-term ceiling for protein synthesis and tissue remodeling.
Trestolone
Also known as (7α,17β)-17-Hydroxy-7-methylestr-4-en-3-one shares a lot in common with Trenbolone as both are part of the same family of derivatives (19-nortestoreone derivatives). In contrast with Trenbolone, Trestolone’s properties also stem from a chemical modification, specifically the addition of a bulky methyl group at the 7th carbon position on the alpha face (the 7a-methyl alteration) of its structure.
This specific spatial arrangement achieves two critically desired pharmacokinetic properties
1: It creates immense steric hindrance (steric hindrance is the name of the interaction when a bulky atom or groups of atoms in a molecule get in the way of other molecules trying to react with it, basically, a physical block) that functionally eliminates interaction with Sex Hormone-Binding Globulin (SHBG).
2: It also simultaneously entirely avoids (or almost) 5a-reductase enzyme metabolism because the enzyme must physically approach the alpha face of the A and B rings to reduce the C4-C5 bond, but this is not possible because it’s geometrically blocked by the protruding methyl group.
It also shares with Trenbolone a similar binding affinity for the AR both in vivo and in vitro, however, in vivo Trestolone experiences some pharmacokinetic issues regarding metabolic clearance and target-site competition because it does not avoid the aromatase enzyme metabolism conversion to E₂.
Simultaneously, this is also the reason Trestolone can self-sustain its own anabolic environment via the Estrogen Receptor Alpha (ERα) loop due to its localized conversion to 7a-methyl-estradiol, which is required to directly upregulate the transcription of the AR itself, consequently continuously increasing nuclear AR density over time facilitating the expansion of the structural capacity for genomic transcription and avoiding the receptor-saturation halt and stunted growth factor expression that heavily affects estrogen deprived cycles. Additionally, Trestolone also possesses extreme tissue selectivity, which allows it to concentrate its immense myogenic potency directly on skeletal muscle without significantly intensifying its effects on non-skeletal muscle tissue, minimizing the risk of experiencing the undesired commonly experienced androgenic side effects from other AAS which are less selective.
Comprehensive Receptor Binding & Potency Data
Non-Genomic AR Pathway
Spoiler: Non-Genomic AR Pathway
The Non-genomic AR Pathway
Unlike the genomic pathway, the non-genomic pathway avoids the slow process of the ligand-AR complex translocating to the nucleus to bind to Androgen Response Elements (AREs) on DNA (which is by the way, quite a slow process, taking around 45+ minutes to initiate transcription and hours to translate folded proteins) by following a completely different sequence of steps which occurs much faster as it’s a transcription-independent cascades that occurs within seconds to minutes, which is the main advantage to leverage.
The Step-by-Step Mechanism:
Instead of waiting for the whole DNA transcription process to occur, this process immediately forces the cytosol to translate existing mRNA into protein, while driving strong cytoskeletal structural changes that pull water and nutrients into the cell. This is why heavily modified super-potent oral AAS like Anadrol exhibit poor classical AR binding affinity but induce immense hypertrophy because they exploit these rapid cascades.
Oxymetholone (also known as 17β-Hydroxy-2-(hydroxymethylene)-17α-methyl-5α-androstan-3-one) (Or commonly known as "Anadrol") is a very potent modified oral AAS derived from dihydrotestosterone (DHT). To put it as simply as possible, it is a DHT molecule that has undergone two critical structural modifications 1. The addition of a methyl group at the 17α position and 2. The attachment of a 2-hydroxymethylene group on the A-ring.
Important disclaimer: Despite the fact Oxymetholone is a DHT derivative, clinical literature suggests the added 2-hydroxymethylene group which significantly alters the ligand's shape might enable it to directly agonize the estrogen receptor (ER) or induce progestogenic activity, causing significant estrogenic effects which are completely independent of aromatase metabolism itself.
What does this achieve? It grants Oxymetholone high oral bioavailability while simultaneously altering both its receptor binding kinetics and metabolic outcome. Now, this structural modifications achieve three critical pharmacological endpoints:
1: It fully avoids interacting with both the 5α-reductase enzyme and with the cytochrome P450 aromatase enzyme complex due to the fact its already 5α-reduced.
(Chemical explanation: This properties are due to its A-ring lacking the C4-C5 double bond required for aromatase metabolism, meaning there is zero conversion to E₂ and it completely avoids 5α-reduction because the 5α-reductase enzyme has no double bond to reduce on the A-ring.)
2: The ligand shows an extraordinarily low binding affinity for both SHBG and the AR. The 17α-methyl and 2-hydroxymethylene groups severely lowers SHBG binding, resulting in a massive free (unbound) fraction of the hormone in circulation.
3.Its 17α-alkylation acts as a steric shield, preventing oxidation by the 17β-hydroxysteroid dehydrogenase enzyme in the liver, making it survive hepatic metabolism and work orally. This also makes it induce liver toxicity to some degree.
All of these properties combined make Oxymetholone such an interesting and unique compound because it induces an extreme muscle accretion which paradoxically occurs despite of its poor AR binding affinity in vitro (which is significantly lower than the one of testosterone or other AAS). This can further be used to demonstrate that its primary mechanism of action relies heavily on the previously described non-genomic pathway rather than the conventional AR genomic pathway. To continue expanding on its extraordinary pharmacokinetic properties, Oxymetholone also possesses the capacity to strongly stimulate erythropoiesis by potently upregulating the synthesis of erythropoietin (EPO) in the kidneys and also directly increasing the responsiveness of erythroid progenitor cells increasing RBC.
To conclude, Oxymetholone is chosen here due to two factors
1: compared to methyldrostanolone (Superdrol) it is much safer on the liver and has more studies and long term data,
2: second is; as previously explained, it's main mechanism of action is not the classic genomic pathway but rather the non genomic pathway as it potently targets surface-level membrane receptors (mAR and ZIP9) which makes it the optimal choice to agonize this intracellular cascade.
Further expanding into its mechanisms, when the rapid interaction with the surface-level membrane receptors occurs, it immediately triggers an intracellular Ca²⁺ influx and phosphorylates the Src/MAPK/ERK cascade. Now this can become in a way a double edged sword because while this cascade is the exact mechanism responsible for rapid cytoskeletal remodeling and massive intracellular swelling in skeletal muscle, mechanistic logic suggests it can simultaneously theoretically degrade skin quality as chronic activation of the MAPK/ERK pathway causes Matrix Metalloproteinase (MMP) upregulation, MMPs being enzymes that downregulate the production of collagen and elastin on the dermis.
Expanding the Cellular binding
Spoiler: Expanding the Cellular binding
To expand the potency of AAS ligands, L-Carnitine (specifically administered via a highly bioavailable route to bypass first-pass hepatic degradation) is deployed as a structural amplifier because it facilitates the mitigation of receptor saturation and expands transcription efficiency which is optimal as the ultimate dead end of genomic signaling is the finite density of ARs inside skeletal muscle tissue.
Clinical literature (e.g., Kraemer et al.) shows that L-Carnitine upregulated AR density in skeletal muscle cells following resistance exercise. Mechanistically, it acts as a selective transcriptomic modulator, increasing the baseline population of available nuclear receptor proteins. By expanding the structural binding pool, it allows a higher volume of circulating Androgen ligands to bind to the expanded AR pool amplifying total muscle protein synthesis (MPS) without necessarily requiring an increase in androgen dosages.
Mitochondrial Acyl-CoA Transport: Beyond the receptor regulation, L-Carnitine serves as a relevant facilitator (substrate) for Carnitine Palmitoyltransferase-1 (CPT-1) because it facilitates the translation of long-chain fatty acids to the inner mitochondrial membrane into the matrix for β-oxidation, this becomes a great tool as heavy androgen transcription and insulin translation place an extreme energy (ATP) demand on the cell, optimizing mitochondrial substrate oxidation grants a needed metabolic buffer, which helps to sustain the high-energy environment required to keep translation steady and active.
Despite all of this, L-Carnitine is theoretically merely a support compound, nothing else.
Cellular Amplifiers (GH & Insulin)
Spoiler: Cellular Amplifiers (GH & Insulin)
Cellular Amplifiers (GH & Insulin)
To unlock another pathway, we will analyze the GH/IGF-1 Axis, one of the main limiting factors of growth is that skeletal muscle fibers operate under a strict myonuclear (or single) capacity, this means a single nucleus can only manage a limited amount of cytoplasm. Now, despite the fact that AAS accelerate muscle protein synthesis, they are relatively less efficient at adding new myonuclei via satellite cell fusion. This is where GH comes into play.
What does Growth Hormone (GH) do?: GH stimulates both hepatic and local production of IGF-1 which makes it a very useful tool, it also possesses another quite interesting mechanism because when mechanical stress or hormonal signaling surges, the IGF-1 gene splices into different isoforms: IGF-1Ec and IGF-1Ea
Their functions:
IGF-1Ec (Mechano-Growth Factor or "MGF") acts locally as an autocrine/paracrine pulse specifically activating dormant satellite cells (muscle stem cells) and stimulating their proliferation, consequently forcing them to bind with damaged muscle fibers and donate their nuclei.
IGF-1Ea (Systemic) isoform follows up MGF by promoting the differentiation of these new cells by permanently expanding the myonuclear pool. Consequently this action increases the overall structural capacity of the muscle fiber to sustain growth without stretching the myonuclear domain beyond its limit.
Its widely known insulin is the most potent anti-catabolic and nutrient-partitioning compound available, and as mentioned before, GH use becomes quite redundant without the use of insulin.
Why do we need insulin?: The simple explanation is that exogenous GH via IGF-1 triggers satellite cell fusion to add new myonuclei to the muscle fiber expanding the total nuclear pool to sustain growth without exceeding the myonuclear domain, now, the issue is this expanded nuclear pool remains translationally very limited (Almost inactive) without the cellular energy required to convert its transcribed mRNA into folded proteins, which insulin solves by accelerating glucose uptake, consequently generating the massive ATP flux required for ribosomal translation.
How does insulin work?: When insulin binds to its extracellular receptor (the tyrosine kinase) it triggers a process known as autophosphorylation (which is when the protein kinase adds a phosphate group to itself), as a result activating Insulin Receptor Substrate 1 (IRS-1), consequently this interaction triggers the next downstream cascade: IRS-1 → PI3K → Akt → mTORC1 which translocates the GLUT4 transporters to the membrane, simultaneously forcing an immediate intracellular influx of glucose and upregulates distinct transporters (such as System A and LAT1) to drive the uptake of amino acids. As a result of this whole process it provides the energy (ATP) and materials required to execute the protein synthesis instructions previously transcribed by the targeted AR genomic pathway.
Insulin & AMPK: To achieve ideal anabolism it requires the unrestricted activation of mTORC1, the issue is massive protein synthesis is very energy consuming and rapidly consumes cellular ATP. This becomes a very big problem because when ATP decreases and AMP levels increase, the cell's primary energy sensor AMPK (5' AMP-activated protein kinase) gets strongly activated by this interaction which then directly phosphorylates and activates TSC2 (which is a tumor suppressor complex) strongly shutting down mTORC1 to preserve energy. To solve this energy crisis and prevent AMPK activation, using insulin is mandatory to shut down this inhibitory mechanism because insulin-activated Akt directly phosphorylates and inhibits TSC2 effectively neutralizing AMPK’s inhibitory action on mTORC1. This synergistic combination of exogenous GH and Insulin keeps the mTORC1 pathway open allowing for sustained protein synthesis while simultaneously maintaining cellular energy homeostasis.
Why Tresiba?: Insulin Degludec (or also known as "Tresiba") in contrast to her other cousins (like Humalog or Novolog) it’s not a rapid-acting insulin. Tresiba is an ultra-long-acting basal insulin that lasts for at least 42 hours in the body; it achieves this pharmacokinetic outcome because it forms multi-hexamers in the subcutaneous tissue, rather than to fix insulin resistance itself, it trades pulsatile sensitivity for a stable and predictable outcome avoiding the chaotic hypoglycemic crashes triggered by rapid-acting insulins like Humalog or Novolog.
This synergistic combination allows GH to potently expand the myonuclear domain while Insulin (Tresiba) simultaneously helps attenuate the consequent blood glucose spike, manages the ATP demand, and prevents the activation of AMPK/TSC2 inhibitory pathway.
Anti-Catabolism
Spoiler: Anti-Catabolism
Spoiler: HPA Axis
Spoiler: GR Antagonism via Trenbolone
Spoiler: GR Antagonism via Mifepristone or Relacorilant
Spoiler: Myostatin Inhibition (TGF-β Superfamily)
Spoiler: The β₂-Adrenergic-Cascade
Spoiler: The GLP-1 Receptor Cascade
Spoiler: The cGMP / PKG Cascade
Infrastructure & Environmental Support
Spoiler: Infrastructure & Environmental Support
Spoiler: The Estrogen Fallacy
Spoiler: eNOS and PPARδ Pathway
Spoiler: The Progestogenic & Pituitary Axis
Spoiler: The Thyroid Hormone Axis (T3/T4)
Spoiler: VGEF Pathway
Conclusion
Spoiler: Conclusion
This thread illustrates how to theoretically maximize and target individual cellular pathways, showing that a multi-pathway saturation is tremendously superior to the strategies seen on Bodybuilding and Looksmaxxing forums. However, this thread only serves as a conceptual model of biological mechanisms rather than the recipe to create an universal stack.
This thread remains strictly a theoretical framework, the combined in vivo interactions of most (if not to say almost all) of these compounds is entirely untested. The individual pathways analyzed and covered on this thread are based in some established molecular biology and isolated individual clinical literature for the compounds that have this kind of data available. However, not all of them do, some have very limited human data or very limited data overall.
Further investigation is required to validate these concepts beyond the theoretical level.
References & Appendix
Spoiler: References
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Mauvais-Jarvis, F., Lange, C. A., & Levin, E. R. (2021). Membrane-initiated estrogen, androgen, and progesterone receptor signaling in health and disease. Endocrine Reviews, 43(4), 720–742. https://doi.org/10.1210/endrev/bnab041
McKoy, G., Ashley, W., Mander, J., Yang, S. Y., Williams, N., Russell, B., & Goldspink, G. (1999). Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation. The Journal of Physiology, 516(2), 583–592. https://doi.org/10.1111/j.1469-7793.1999.0583u.x
Miyazaki, M., McCarthy, J. J., Fedele, M. J., & Esser, K. A. (2011). Early activation of mTORC1 signalling in response to mechanical overload is independent of phosphoinositide 3‐kinase/Akt signalling. The Journal of Physiology, 589(7), 1831–1846. https://doi.org/10.1113/jphysiol.2011.205658
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Appendix:
Abreviations:
11ẞHSD2: 11ẞ-hydroxysteroid dehydrogenase type 2
AAS: Anabolic Androgenic Steroids
ACTH: Adrenocorticotropic hormone
AI: Aromatase Inhibitor
AMP: Adenosine monophosphate
AMPK: 5' AMP-Activated Protein Kinase
AR: Androgen Receptor
ARE: Androgen Response Element
ARBS: Angiotensin II Receptor Blockers
ATP: Adenosine triphosphate
cAMP: Cyclic adenosine monophosphate
cGMP: Cyclic guanosine monophosphate
CPT-1: Carnitine Palmitoyltransferase-1
D2: Dopamine Receptor (specifically the D2 subtype)
DHT: Dihydrotestosterone
E2: Estradiol
eNOS: Endothelial Nitric Oxide Synthase
ERa: Estrogen Receptor Alpha
GAP: GTPase-activating protein
GCR/GR: Glucocorticoid Receptor
GH: Growth Hormone
GLP-1: Glucagon-Like Peptide-1
GLUT4: Glucose Transporter Type 4
HIF-1α: Hypoxia-Inducible Factor 1-alpha
HPA: Hypothalamic-Pituitary-Adrenal (axis)
HSP: Heat Shock Proteins
IC50: Half-Maximal Inhibitory Concentration
IGF-1: Insulin-like Growth Factor 1
IRS-1: Insulin Receptor Substrate 1
Kd: Dissociation Constant
Ki: Inhibition Constant
LAT1: L-type amino acid transporter 1
LBD: Ligand-Binding Domain
LVH: Left Ventricular Hypertrophy
mAR: Membrane Androgen Receptor
MAPK: Mitogen-activated protein kinase
MENT: Methyl-nortestosterone (Trestolone)
MGF: Mechano-Growth Factor (also known as IGF-1Ec)
MMP: Matrix Metalloproteinase
MPB: Muscle Protein Breakdown
MPS: Muscle Protein Synthesis
MR: Mineralocorticoid Receptor
mTORC1: Mechanistic Target of Rapamycin Complex 1
PDE5I: PDE5 inhibitors
PgR: Progesterone Receptor
PI3K: Phosphoinositide 3-Kinase
PKA: Protein Kinase A
PKG: Protein Kinase G
PPAR: Peroxisome Proliferator-Activated Receptor
RBA: Relative Binding Affinity
SHBG: Sex Hormone-Binding Globulin
SR: Sarcoplasmic Reticulum
T3: Triiodothyronine
T4: Thyroxine
TGF-β: Transforming Growth Factor-beta
TR: Thyroid Hormone Receptor
TSC2: Tuberous Sclerosis Complex 2
VEGF: Vascular Endothelial Growth Factor
Defintions:
Adenylate Cyclase: A membrane-bound enzyme that catalyzes the conversion of ATP into cyclic adenosine monophosphate (cAMP). It serves as the primary effector for Gs-protein-coupled receptors, initiating intracellular signaling cascades.
Akt (Protein Kinase B): A critical cytosolic serine/threonine-specific protein kinase that plays a key role in multiple cellular processes such as glucose metabolism, apoptosis, cell proliferation, and transcription. It acts as the primary downstream effector of PI3K to stimulate mTORC1.
AMPK (5' AMP-Activated Protein Kinase): A central cellular energy sensor enzyme. It is activated by rising AMP levels (indicating cellular energy depletion) and acts to restore ATP homeostasis by shutting down energy-consuming anabolic pathways, such as mTORC1-mediated protein synthesis.
Androgen Receptor (AR): A single nuclear receptor protein encoded by the NR3C4 gene. Structurally composed of an N-terminal transactivation domain, a central DNA-binding domain, and a C-terminal ligand-binding domain (LBD), it acts as a ligand-dependent transcription factor.
Angiogenesis: The physiological process through which new blood vessels form from pre-existing vessels. It is primarily driven by signaling molecules such as VEGF (Vascular Endothelial Growth Factor) in response to localized tissue hypoxia.
Aromatization: The enzymatic biotransformation of specific androgens into corresponding estrogenic substrates via the cytochrome P450 aromatase enzyme complex.
Autocrine / Paracrine Signaling: Forms of cell-to-cell communication. Autocrine signaling occurs when a cell secretes a hormone or chemical messenger that binds to receptors on its own surface. Paracrine signaling occurs when these messengers act on nearby, adjacent cells.
Calpains: A family of calcium-dependent, non-lysosomal cytosolic proteases. Unlike the ubiquitin-proteasome pathway which degrades tagged proteins, calpains actively cleave and break down intact structural muscle proteins (like titin and nebulin) during periods of high intracellular calcium.
E3 Ubiquitin Ligase: A specialized family of enzymes (e.g., MuRF-1, Atrogin-1) that catalyze the attachment of ubiquitin molecules to target proteins. This "tagging" identifies the protein for degradation by the 26S proteasome, a critical step in muscle protein breakdown (MPB).
G-Protein Coupled Receptor (GPCR): A large family of cell surface receptors that detect extracellular signals and activate internal signal transduction pathways. They consist of seven transmembrane helices and are categorized by the type of G-protein (Gs, Gi, Gq) they recruit.
GLUT4 (Glucose Transporter Type 4): An insulin-regulated glucose transporter found primarily in adipose tissues and striated muscle (skeletal and cardiac). Upon activation of the PI3K/Akt pathway, GLUT4 translocates from intracellular vesicles to the plasma membrane to facilitate glucose uptake.
Hypoxia-Inducible Factor 1-alpha (HIF-1alpha): A transcription factor that acts as the master regulator of oxygen homeostasis. Under hypoxic conditions, it avoids degradation and translocates to the nucleus to initiate the expression of genes involved in angiogenesis and metabolic adaptation.
IC50 (Half-Maximal Inhibitory Concentration): A quantitative measure indicating the precise concentration of a ligand required to displace exactly 50% of a reference radiolabeled ligand from a receptor population pool. A lower IC50 indicates exponentially higher binding affinity.
In vivo / In vitro: Latin terms used in research. In vivo refers to biological processes or experiments occurring within a whole, living organism. In vitro refers to processes studied in a controlled, isolated environment outside of a living organism (e.g., in a test tube or petri dish).
Ligand: A specific molecule or atom that can bind to a receptor either irreversibly or reversibly to initiate, modulate, or inhibit a cellular signaling cascade (e.g., Testosterone, Dihydrotestosterone).
Ligand-Binding Domain (LBD): A highly specialized, hydrophobic pocket within a receptor structure designed to exclusively accommodate a compatible ligand, inducing a conformational fold that activates the receptor complex.
Matrix Metalloproteinase (MMP): A group of zinc-dependent endopeptidases capable of degrading extracellular matrix proteins. While vital for tissue remodeling, chronic overexpression (e.g., via sustained MAPK signaling) can lead to the degradation of dermal collagen and elastin.
Myonuclear Domain: The theoretical volume of cytoplasm managed by a single myonucleus. Because muscle fibers are multinucleated, the physical limit of this domain dictates that total fiber hypertrophy is limited by the number of nuclei available; myonuclear addition (via satellite cell fusion) is required to expand this structural ceiling.
Phosphodiesterase-5 (PDE5): An enzyme that catalyzes the hydrolysis of cGMP to 5’-GMP. By inhibiting this enzyme, cGMP levels are sustained, facilitating prolonged smooth muscle relaxation and enhanced vascular perfusion.
PI3K (Phosphoinositide 3-Kinase): A family of enzymes that phosphorylate the 3-position hydroxyl group of the inositol ring of phosphatidylinositol. It is the crucial upstream mediator that translates insulin receptor signaling into the activation of Akt.
PKA (Protein Kinase A): A family of enzymes whose activity is dependent on cellular levels of cAMP. Once activated, PKA phosphorylates specific target proteins to alter their function, playing a critical role in lipid metabolism and anti-catabolic signaling.
PPARbeta/delta (Peroxisome Proliferator-Activated Receptor Delta): A nuclear hormone receptor that acts as a central metabolic regulator, orchestrating lipid oxidation, skeletal muscle fiber type switching, and mitochondrial biogenesis.
Relative Binding Affinity (RBA): A comparative mathematical ratio indicating how tightly a specific synthetic compound binds to a target receptor relative to a reference native hormone (typically Testosterone or Dihydrotestosterone), which is arbitrarily set at a baseline value of 100.
Rheb (Ras homolog enriched in brain): A small GTPase that is a direct activator of mTORC1. Rheb's activity state is controlled by the TSC2 complex: when bound to GTP, Rheb is active and stimulates mTORC1; when TSC2 exerts its GAP activity, Rheb is converted to its inactive GDP-bound state, inhibiting mTORC1.
Sarcoplasmic Reticulum (SR): A specialized type of smooth endoplasmic reticulum found exclusively in myocytes (muscle cells). It acts as a dedicated storage and release sink for calcium ions (Ca2+), regulating muscle contraction.
Satellite Cell: A quiescent, muscle-specific stem cell located between the sarcolemma and the basal lamina of a muscle fiber. Upon activation (e.g., by MGF or mechanical stress), these cells proliferate and fuse with existing muscle fibers to provide additional nuclei.
SHBG (Sex Hormone-Binding Globulin): A glycoprotein that binds to androgens (such as testosterone) and estrogens with high affinity. By sequestering these hormones in the blood, SHBG limits the fraction of "free" (bioavailable) steroid hormone capable of entering the cell to bind with the AR.
TSC2 (Tuberous Sclerosis Complex 2 / Tuberin): A tumor suppressor protein that forms a complex with TSC1. It acts as a GTPase-activating protein (GAP) for Rheb, effectively serving as the "energetic kill-switch" for the mTORC1 pathway.
