Page 49 of Get Serious: “Your training progress will be suboptimal should squats be excluded from your regimen. So don’t even think about it. And no, you cannot exchange leg extensions for squats.”
Here’s why. And I cite the same page of my recently released book. “Heavy squats generate a robust hormonal response as numerous muscular structures are traumatized during the movement.”
Need proof? Check out this study in the April 2014 volume of The Journal of Strength and Conditioning Research (published by the NSCA): The Acute Hormonal Response to Free Weight and Machine Weight Resistance Exercise. Shaner, et al. compared the effects of resistance exercise on acute hormonal responses in a cohort of men performing similar lower body exercises, namely a machine-based leg press and the squat. Here’s what they found. Squats increased serum testosterone and growth hormone to a greater degree than did the leg press in the acute phase, post-exercise. Serum cortisol was also elevated to a greater extent in those performing the back squat relative to the leg press group. Why? More bodily stress equates to a more robust elevation in cortisol and secondarily recovery hormones such as GH and testosterone.
But the leg press and squat are very similar movements mechanistically, right? WRONG. Have you ever done a set of 20-rep squats? Your upper body will be taxed nearly to the extent of your lower body. Because it is bearing the loaded bar. Simply standing there with a loaded bar on your shoulders taxes the hell out of your lumbar extensors, abdominal musculature and biceps. It is this additional muscular stimulation (trauma, if you will) associated with the back squat that is responsible for the more robust hormonal response relative to the machine-based leg press.
This data should not be misconstrued. Machine-based training has its place. I’ve done loads of it (no pun intended) during the last 30 years and have responded quite well. Free-weight training however, more specifically the 5 “Pillar Exercises” outlined in Get Serious, will evoke far greater physiological responses (and adaptation) than most machine-based correlates. So don’t waste your time on a Nautilus biceps curl when there stands a chin/pull-up bar in close proximity…