We previously reported that the ability of elderly people to perform stretch-shortening cycle movement (SSC) would play an important role in maintaining their walking ability. This study investigated the efficacy of a bouncing squat test to evaluate SSC ability in elderly people who had developed weakness in the neuromuscular-tendon complex of the legs. Eight elderly people (aged 83.6 ± 6.3 yr, range 73-93 yr) performed repetitive bouncing squats (BS) and rebound jumps (RJ), as well as three types of gait with different stride length (free, wide, ultra-wide). Kinematic data and ground reaction forces were recorded using a video camera and a force platform, respectively. All subjects were able to perform BS, but three older subjects were unable to perform RJ. The maximal vertical ground reaction force (F
max) was highest for RJ (3.02 ± 0.73 N · BW
-1), followed in descending order by BS (1.63 ± 0.25 N · BW
-1), ultra-wide (1.28 ± 0.17 N · BW
-1), wide (1.19 ± 0.11 N · BW
-1), and free walking (1.06 ± 0.05 N · BW
-1). These results suggest that BS is a safe and suitable exercise for the elderly whereas RJ is not. F
max, the maximum of negative (P
-max) and positive vertical power (P
+max) during BS, decreased significantly with aging (F
max, r=-0.861, p<0.01; P
-max, r=-0.949, p<0.001; P
+max, r=-0.932, p<0.001). Also, there was a significant correlation between the power during BS and each component of the ground reaction force during free walking (negative peak force, r=0.853, p<0.01; positive peak force, r=0.780, p<0.05; vertical peak force, r=0.833, p<0.01; negative impulse, r=0.859, p<0.01; positive impulse, r=0.712, p<0.05). These results indicate that BS power could be a suitable indicator for evaluating SSC ability in relation to walking ability. Moreover, BS may be an effective training method for improvement of walking ability in elderly people.
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