Aaron Shaner and colleagues investigated the effects of using a multi-joint free weight leg exercise versus a multi-joint machine leg exercise on anabolic hormone responses. They measured both during and immediately after a lift (i.e., multiple and repeated sets).
Studying a classic high-volume, mus-cle-building set-rep scheme, this group of researchers had 10 resistance trained men in their early to late 20s each complete 6 sets of 10 repetitions of squats (free weight) and leg presses (machine) at the same relative intensity, in two separate training sessions that were separated by 1 week.
Compared to the multi-set leg press protocol, testosterone and growth hormone were elevated to a greater extent immediately after performing the multi-set squat protocol. Also, 15 and 30 minutes post-squat protocol, growth hormone was still elevated to a greater extent, compared to the leg press protocol.
Even though certain machine-based exercises may feel as challenging as free weight-based exercises, this study suggests that free weight exercises lead to greater acute muscle growth-promoting, anabolic hormone responses than machine weight exercises that use similar lower body multi-joint movements and primary muscle groups/movers.
By in-corporating predominantly free weight exercises into your lifts, this type of very short-term/immediate (acute) anabolic hormone response, expe-rienced lift-after-lift, may translate into superior muscular size and perfor-mance improvements over a longer period of weight training.
[Shaner, Aaron A., et al. “The acute hormonal response to free weight and machine weight resistance exercise.” The Journal of Strength & Condi-tioning Research 28.4 (2014): 1032-40.]