What Drives Muscle Growth & What Doesn't | Dr. Mike Roberts

Mike Roberts detailed Cody Han's study where trained men performed 3 full-body sessions per week with weekly progressive volume increases: starting at 3-4 sets/exercise, reaching 32 sets by week 6. Biopsies, DEXA, and bioimpedance at weeks 3 and 6 showed that while 32 sets did not yield more lean mass than 20, it caused a disproportionate rise in extracellular water, indicating inflammation/fluid shifts. Therefore, 20 sets appeared as the sweet spot for maximizing true muscle growth while avoiding negative side effects. He acknowledges that individual response varies, so some may need 12, others 20. This practical threshold aligns with other labs' recent findings.

Mike discussed their acute biopsy study in well-trained individuals, showing global mRNA and mTOR signaling were indistinguishable 3 and 6 hours after 30% or 80% failure training. He linked this to Stu Phillips' muscle protein synthesis data. The critical factor is reaching near failure, not the absolute load, because that's what maximizes mechanical tension per motor unit. He also noted that the total volume load (weight × reps) matched between protocols, giving a plausible explanation. For those who prefer heavy, go heavy; if you want to test your resolve, do the 40-rep sets.

Mike described a study (Polom) where prior resistance training followed by endurance training backfired, showing that priming muscle for hypertrophy hindered mitochondrial gains—indicating the complexity of signaling beyond AMPK/mTOR. He then referred to Jake Wilson's meta-analysis that concluded SIT on a bike, at low frequency and volume, is the least interfering form of concurrent endurance training. He explained that long slow distance and high-impact modalities like running create more muscle damage and possibly compete for recovery resources, making it harder to grow muscle. He also mentioned that SIT maintains power output and may preserve strength better.

Mike cited Max Michelle's dissertation: 11 trained and untrained men/women underwent 2 weeks of knee bracing. The rate of VL atrophy was the same, but trained individuals preserved more absolute muscle mass. Retraining for 8 weeks after bracing showed that previously untrained individuals (newbie gains) outpaced the trained, but trained regained baseline quickly. He also mentioned Matt Stock's work on action imagery, Darren Candow's creatine during bracing, and Arie Ferondo's high-dose EAAs. Andy Galpin added his anecdote of pre-surgery 'muscle banking' in elite athletes, supporting the strategy.

As discussed in whats_new entry, Plotkin's dissertation is testing this directly. Mike initially skeptical but now intrigued by literature. Japanese studies and Schoenfeld's 2025 data add weight. The practical application: perform the bottom half of a movement where the muscle is maximally stretched, e.g., only the bottom half of a leg press. This could be a game-changer for those who've stalled on traditional ROM.

Mike discussed the first GWAS for hypertrophy, showing only one significant SNP in Glee3, which requires validation. He emphasized that the response is far too complex for a single polymorphism to determine, and the current state of science does not support actionability. He cautioned that companies marketing such tests are premature and potentially misleading.

As covered, Roberts detailed that neither total testosterone, free testosterone, nor muscle androgen receptor content predicted hypertrophy. Even when endogenous testosterone was pharmacologically lowered to subclinical levels, some hypertrophy still occurred. Thus, the practical message is: don't let a 'low-normal' T result discourage you or cause you to change a program that's based on mechanical overload principles.

Mike cites Stu Phillips' recent review and Abby Mackey's data indicating very low true non-response. He emphasizes that many low responders in standard low-volume protocols may respond when volume is increased. The landmark high-volume study from his lab (Cody Han) demonstrated that some individuals who didn't grow at moderate volumes responded to 20+ sets per week. He also notes that even low responders gain strength, highlighting neurological adaptations. The key implication: if you're not growing, the first step is to check and likely increase training volume, not give up.

Initially, Stu Phillips found a correlation between muscle AR content and hypertrophy, but Roberts' lab with Cody Han found no such association in trained men undergoing a 6-week high-volume program. Subsequently, a larger study with 40 individuals (20 men, 20 women) by Clayton Labardi and Roberts examined both androgen and estrogen receptor levels before and after training; neither predicted hypertrophy. Roberts concludes that while receptor dynamics may play a small role across the lifespan, within normal young adult ranges, they are not predictive, and buying tests is a waste of money.

In an unpublished analysis from Dustin Lewis, Roberts' lab trained older and younger cohorts for 12 weeks and performed global proteomics on muscle biopsies. The young cohort displayed robust proteome alterations and enrichment of proteostasis pathways, while the older cohort showed a stark lack of proteome remodeling, indicating impaired protein turnover. This was not due to differences in hormonal status; the blunted response was traced to the muscle's own protein machinery, including ribosomal deficits and failure to clear damaged proteins. This highlights the need to target muscle-specific protein homeostasis when designing interventions for sarcopenia.