The New Science of Muscle Growth: What Works and What Doesn't?
A thorough look at mechanical tension, “the pump”, hormone spikes and other myths, debunked.
A comprehensive new review from McMaster University has systematically dismantled several long-standing myths about what drives muscle growth, revealing that many popular training strategies used by lifters worldwide, from chasing "the pump" to manipulating hormones through specific workout protocols, have no meaningful impact on building muscle. Led by researchers Derrick Van Every, Matthew Lees, Brandan Wilson, Jeff Nippard, and Stuart Phillips, this evidence-based analysis examined decades of research to determine what truly matters for muscle hypertrophy and what's simply gym folklore.
The review confirms that mechanical tension—the force generated when muscles contract against resistance—is the primary and most potent driver of muscle growth. Other popular concepts like metabolic stress, acute hormonal spikes, cellular swelling, and even sarcoplasmic hypertrophy either play no meaningful role or are vastly overstated in their importance. For everyday lifters, this means training programs should focus on progressive overload, sufficient volume, and training close to failure rather than chasing transient physiological responses that feel productive but don't actually contribute to long-term muscle growth. Perhaps most valuably, the authors also provide realistic expectations for muscle gain: untrained males can expect to gain approximately 1.53 kg of fat-free mass over 10–12 weeks of training, with long-term natural lifters averaging 2.5-4.0 kg per year over a 5-year training period.
Aim
The review aimed to critically evaluate persistent misconceptions about resistance training-induced muscle hypertrophy and contrast them with evidence-based mechanistic insights. Specifically, they examined the role (or lack thereof) of systemic hormones, metabolites, and cell swelling in promoting muscle hypertrophy. They also critically reviewed the concept of sarcoplasmic hypertrophy to provide evidence-based, realistic expectations for muscle growth to help scientists, trainees, and practitioners understand what truly drives muscle development.
Methods
As a comprehensive review paper, the authors synthesised evidence from multiple research methodologies, including unilateral training studies, meta-analyses, tracer studies measuring protein synthesis, and both acute and chronic resistance training interventions. They examined studies using various measurement techniques such as MRI, CT scans, ultrasound, dual-energy X-ray absorptiometry (DXA), and muscle biopsies to assess changes in muscle cross-sectional area and fiber size. The review incorporated data from studies ranging from single-session acute protocols to long-term interventions lasting up to 24 weeks, examining populations from untrained individuals to competitive bodybuilders and powerlifters.
Results
Hormones Don’t Drive Hypertrophy
The evidence overwhelmingly demonstrates that acute post-exercise elevations in testosterone, growth hormone, and IGF-1 do not enhance muscle protein synthesis or hypertrophy. In a pivotal unilateral training study by Wilkinson and colleagues, 10 young males trained one leg three times weekly for 8 weeks. Despite no changes in systemic hormone concentrations following exercise, the trained leg exhibited significant hypertrophy, with a 22% increase in muscle cross-sectional area and a 22% and 13% increase in the cross-sectional area of type IIx and IIa muscle fibres, respectively (p < 0.05). Strength also improved substantially in the trained leg (leg press: +25 kg; knee extension: +21 kg, both p < 0.05), while the untrained leg showed no changes.
West and colleagues extended this research with a 15-week unilateral training protocol where one arm was exposed to high hormone conditions (elevated testosterone, growth hormone, and IGF-1) by performing intense leg exercises, while the other arm performed only elbow flexor exercises in a low-hormone environment. Despite consistently greater post-exercise hormone elevations in the high-hormone arm, both conditions resulted in nearly identical increases in muscle cross-sectional area (low-hormone = 12% ± 2% vs. high-hormone = 10% ± 2%, p > 0.05) and similar strength gains.
Supporting this, West and Phillips examined post-exercise hormonal responses in a cohort of 56 participants. They reported that none of the rises in growth hormone, free testosterone, or IGF-1 were significantly correlated with gains in lean body mass or improvements in leg press strength. Furthermore, if hormones were primary regulators of hypertrophy, males, and females would show dramatically different muscle-building responses, given that males have 10-20 fold higher total testosterone and up to 200-fold higher free testosterone concentrations. Yet multiple meta-analyses have confirmed that males and females experience similar relative increases in muscle mass and strength following resistance training.
Metabolic Stress Is Not Anabolic
The review found no convincing evidence that metabolites such as lactate, inorganic phosphate, and hydrogen ions meaningfully contribute to muscle hypertrophy. While bodybuilding protocols (8-12 repetitions with short rest intervals) generate greater metabolic stress compared to powerlifting-style training (1-5 repetitions), both approaches promote similar hypertrophy gains when volume-load is equated.
