This study aimed to investigate the effect of explosive-type strength training of plantar flexors on muscle strength and postural stability. Participants were 22 healthy older adults divided into two groups: the training group (n = 12) and the control group (n = 10). Participants in the training group underwent explosive-type strength training for 4 weeks (2 days per week). Training consisted of 3 sets of 10 repetitions of explosive plantar flexion lasting less than 1 s. In the pre- and post-training phases (PRE and POST, respectively), we measured plantar flexor muscle thickness using ultrasonography. We also measured the maximum voluntary torque (MVT) during maximum voluntary isometric plantar flexion and rate of torque development (RTD) during explosive isometric plantar flexion lasting less than 1 s; the duration of singleleg standing; and the Center of Pressure (CoP) sway during single-leg standing. In the training group, MVT and RTD in POST significantly increased compared with those in PRE (p < 0.05). However, plantar flexor muscle thickness did not change. The duration of single-leg standing in POST was significantly longer compared with that in PRE (p < 0.05). In addition, the area of CoP sway during single-leg standing was significantly decreased in POST (p < 0.05). These findings suggest that explosive-type strength training increases MVT and RTD, which may contribute to improvement of postural stability.

DESCENTE SPORTS SCIENCE Vol.36/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE