From Ergo Log
Squats create a stronger anabolic stimulus in the body than equally heavy sets on a leg press machine. Sports scientists from the University of North Texas report on this in the Journal of Strength and Conditioning Research. The Texans discovered that bodybuilders synthesise more growth hormone and testosterone after a squat session than after a session on a leg press machine.
Strength training done with bars and dumbbells produces better results than using machines. Training with free weights is also better for physical coordination and stimulates more muscle groups than training with machines does. Whats more, the movements you make with free weights tend to be more natural and therefore injuries are less likely to happen.
Whether training on machines or with free weights also has different physiological effects is not known. That's why the Texans did an experiment with ten well-trained male strength athletes average age 25 years who trained their legs on two occasions: on one occasion doing squats and on another using the leg press. Both times the athletes did 6 sets of 10 reps. For each training session they used weights that were 80 percent of the weight at which they could just manage 1 rep [1RM].
Immediately after the session [IP], and 15 and 30 minutes later, the researchers observed that the concentration of testosterone and growth hormone in the men's blood was higher than the previous measurement. But the increase in the two muscle-building hormones was considerably higher after the squat training than after the leg-press training session.
The men found both kinds of training session equally tiring.
When the researchers calculated the amount of effort the men had expended during the two sessions, they discovered why the concentrations of growth hormone and testosterone were higher after the squat session. Although the men used more weight on the leg-press machine their exertion was 42 percent higher during the squat session.
That's because the men also had to work against their own bodyweight during the squats, and because the range of movement is greater during a squat than when using the leg press.
"At similar intensities and ratings of perceived exertion, the free weight (squat) exercise produces a greater acute hormonal response than the machine weight (leg press) exercise", the researchers summarise. "The strength and conditioning professional should therefore consider choosing free weight exercises over machine weight analogs to induce a greater acute hormonal response, as this might subsequently result in superior physiological adaptations."
The publication is based on the thesis written by the first author, Aaron Shaner. See here.
J Strength Cond Res. 2013 Nov 22. [Epub ahead of print].