PHYS-33 · Principle
Do heavy squats boost testosterone and build more muscle?
Hard sessions raise testosterone, growth hormone and cortisol for minutes, but in trials the size of the rise did not predict gains, and the cortisol rise is normal, not harm.
How the body works, as far as the reviews below go: they disagree, and the entry gives both readings. A study entry shows what one experiment measured.
Practical Application
Do heavy squats boost testosterone and build more muscle? Hard sessions raise testosterone, growth hormone and cortisol for minutes, but in trials the size of the rise did not predict gains, and the cortisol rise is normal, not harm.
What it means for training: choose a session for the load, effort and volume it brings, not for its hormone response; the leading candidate stimulus for growth is mechanical (REF-682).
Mechanism
High-volume, moderate-to-heavy sessions with short rests and a large muscle mass raise testosterone, growth hormone and cortisol most, for about 15-30 min (Kraemer & Ratamess 2005); a review sets out both the "hormone hypothesis" and the view that the rise mobilises fuel (Schoenfeld 2013).
In 8 young men, adding leg work that raised testosterone, growth hormone and IGF-1 did not raise biceps protein synthesis (West 2009); in 56 young men over 12 weeks the acute rises did not correlate with strength, while cortisol and growth hormone weakly tracked fibre growth (West & Phillips 2012); in 49 trained men no acute rise related to gains (Morton 2016).
The response varies between people and with fatigue: after a 2-h run cortisol rose in half of 12 athletes and not in the rest (REF-1247, B-).
Common misreading
"Train legs to make your arms grow"; "cortisol after training is catabolic, so keep sessions short"; "the bigger the spike, the better the session".