Areas where scientific evidence is lacking or incomplete.
Current data on clinical efficacy and long-term risks of GHS like sermorelin, ibutamoren, and ipamorelin are largely lacking, particularly for specific populations.
Implications: Cannot establish definitive safety profiles for cardiovascular events, cancer risk, and sustained metabolic improvements.
Specific 'best practices' or 'minimal effective doses' are not yet defined. Reported dosing varies widely and is not standardized for prescriptive medical use.
Implications: Users rely on anecdotal protocols with high personal variation.
The mechanism of action for E-domain peptides (the C-terminal of MGF) remains an 'unanswered question'. Unclear if the endogenous E-domain functions independently or only as part of a prohormone.
Implications: Synthetic MGF peptides may not replicate endogenous effects.
In follistatin gene therapy trials, increased muscle size did not necessarily result in proportional increase in force generation. Myostatin mutations induce massive growth but can impair specific force.
Implications: Hypertrophy interventions may not translate to functional strength gains.
Females comprised only 23.9% of participants in human interventional studies and less than 13% of rodents in reviewed literature.
Implications: Findings may not generalize to female populations.
The status of peptides like CJC-1295 and ipamorelin is in 'limbo' with the FDA, which discourages standardized clinical research and limits legal access for human study.
Implications: Creates a self-reinforcing cycle of 'no data' justifying continued restrictions.
Expert disagreements and competing evidence.
IGF-1 is NOT required
Follistatin retained full hypertrophic effect in hypophysectomized animals despite very low concentrations of muscle and circulating IGF-1.
Source: Hypophysectomy studies
IGF-1 receptor IS mandatory
Follistatin-mediated hypertrophy is regulated by mTOR and may be associated with increased insulin action; a functional IGF-1 receptor is often cited as mandatory.
Source: mTOR pathway studies
Resolution
Discrepancy may relate to different experimental models and measurement techniques.
MGF acts independently of IGF-1R
MGF exhibits neuroprotective and regenerative effects independent from IGF-1R stimulation and does not require the receptor's canonical binding site.
Full-length MGF directly stimulates IGF-1R
Experimental results demonstrate that full-length MGF directly stimulates the IGF-1R with maximal potency similar to recombinant human IGF-1 at high concentrations.
Resolution
Synthetic MGF peptides (Goldspink-MGF) failed to activate the receptor, which may explain the discrepancy between full-length and fragment studies.
GH is NOT anabolic in healthy adults
Very little evidence supports an anabolic role for supraphysiological systemic GH in skeletal muscle of healthy individuals; muscle mass gains are generally not observed.
GH secretagogues improve body composition
GH secretagogues can significantly improve body composition; massive GH release from heat stress can increase anabolism and dramatically improve performance.
Size gains without strength
A 15-week study found that while collagen peptides significantly amplified muscle volume increases, they did not enhance strength gains (MVT or 1RM) compared to placebo.
Collagen augments strength
Prior studies (Zdzieblik et al., Jendricke et al.) reported that collagen supplementation augmented strength gains significantly more than placebo.
Proportional strength gains
Follistatin delivery in non-human primates induced pronounced increases in both muscle size AND strength.
Hypertrophy without force
Myostatin mutation or blockade leads to hypertrophy without corresponding increase in muscle force, attributed to mitochondrial depletion in enlarged muscle.