Regional and muscle-specific adaptations in knee extensor hypertrophy using flywheel vs. conventional weight-stack resistance exercise.

This study compared the effects of the most frequently employed protocols of flywheel vs. weight-stack resistance exercise (RE) on regional and muscle-specific adaptations of the knee extensors. Sixteen men (n=8) and women (n=8) performed 8 weeks (2-3 days/wk) of knee extension RE employing flywheel technology (FW) on one leg (4x7 repetitions), while the contralateral leg performed regular weight-stack (WS) training (4x8-12 repetitions). Maximal strength (1RM in WS) and peak FW power were determined before and after training for both legs. Partial muscle volume of vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI) and rectus femoris (RF) were measured using magnetic resonance imaging (MRI). Additionally, quadriceps (QF) cross-sectional area was assessed at a proximal and a distal site. There were no differences (P>0.05) between FW vs. WS in muscle hypertrophy of the QF (8% vs. 9%), VL (10% vs. 11%), VM (6% vs. 8%) or VI (5% vs. 5%). Muscle hypertrophy tended (P=0.09) to be greater at the distal compared with the proximal site, but there was no interaction with exercise method. Increases in 1RM and FW peak power were similar across legs, yet the increase in 1RM was greater in men (31%) than in women (20%). These findings suggest that FW and WS training induce comparable muscle-specific hypertrophy of the knee extensors. Given that these robust muscular adaptations were brought about with markedly fewer repetitions in the FW compared with WS, it seems FW training can be recommended as a particularly time-efficient exercise paradigm.