TESTOSTERONE AND GH RESPONSES: FREE WEIGHTS VS. MACHINES

All forms of resistance training provide a stimulus that induces an anabolic-hormonal response, which contributes to adaptations associated with weight training such as muscle growth and strength. More precisely, weight training causes an increase in the two most prominent muscle-building hormones, testosterone and growth hormone (GH). Testosterone drives muscle growth by stimulating muscle protein synthesis and inhibiting muscle protein degradation. GH triggers greater muscle growth primarily by stimulating the production of insulin-like growth factor 1 (IGF-1), which has been shown to also potently stimulate muscle growth by increasing muscle cell protein synthesis.

Michael J. Rudolph

That said, not all weight-training protocols are as effective at inducing an increase in anabolic hormone levels – suggesting that the increase in anabolic hormone from weight training is dependent on factors associated with training program variables such as exercise intensity and training volume, as well as the type of training equipment used such as free weights or exercise machines. While many studies have investigated the influence of such variables as training intensity and volume on the anabolic hormone response, only recently has the hormonal response to free weights and machine exercise training been compared, showing a considerable difference between these two training modalities.

Anabolic Hormone Levels

Because the apparent discrepancy between free weights and machines on the anabolic hormone response to training had been unexamined, Shaner et al. investigated the effect of a similar free-weight movement (squat) and machine exercise (leg press) on anabolic hormone response. In this study, 10 young men with weight training experience completed six sets of 10 repetitions of squats or leg presses at the same relative intensity one week apart. After each exercise session, blood samples were analyzed for testosterone, GH, and cortisol concentrations. The results of the study by Shaner et al. showed that testosterone levels were considerably higher after performing the squat when compared to the leg press. The authors suggest that this difference may be due to the greater amount of muscle mass recruited during the squat8 that has clearly been shown to be an important factor that enhances testosterone production. In addition, while GH concentrations were elevated after the squat and leg press, the increase was much greater after performing the squat. Because lactate production has been shown to trigger GH secretion10, the authors propose that the larger increase in GH from squatting is also likely due to the greater amount of activated muscle mass, which generates more lactate and triggers more GH release.