Efficacy of manual versus free-weight training to improve maximal strength and performance for microgravity conditions

We tested a simple and compact device designed for manual resistance training in conditions of microgravity (Self-Powered Rope Trainer Duo (SPoRT Duo)) to increase muscle performance. Twenty-four participants (20.8 +/- 2.1 years) were randomly assigned to a manual resistance group (n = 12) and a free-weight group (n = 12). Participants performed eight exercises (three sets; 8-12 efforts) either with free weights or the SPoRT Duo twice a week for 6 weeks. Maximal isometric force of trunk flexion, back extension and chest press increased (P at least 0.01, d at least 0.52) both in the manual resistance group (18.4% +/- 15.0%; 32.7% +/- 22.7%; 15.3% +/- 9.7%) and free-weight group (18.0% +/- 13.9%; 26.6% +/- 28.9%; 13.3% +/- 7.6%). The change in maximal isometric force of wide grip row in both groups (d at best 0.38) did not reach statistical significance (P at best 0.08). The squat one-repetition-maximum increased in the manual resistance group (29.8% +/- 22.1%) and the free-weight group (32.4% +/- 26.6%). Jump height, determined by a jump-and-reach test, increased in the free-weight group (9.8% +/- 13.2%) but not in the manual resistance group (2.0% +/- 8.5%). Manual resistance training was equally effective in increasing strength as traditional resistance training with free weights. This apparatus is a useful addition to current in-flight exercise systems.