The effects and mechanisms of whole body vibration training on muscle, balance and physical performance in community dwelling individuals with sarcopenia

Abstract

Sarcopenia is an age-related loss of skeletal muscle mass that predisposes seniors to falls, disability and mortality. Exercise training was proved to be effective for improving the muscle and physical performance in seniors with sarcopenia. In the past decade, a new style of training, whole-body vibration (WBV), has been reported as an effective approach to improve the neuromuscular, balance and functional performance in the healthy elderly people. However, the effects of WBV on muscle, balance and physical performance in the people with sarcopenia are still uncertain and there is no consensus on the optimal parameters with WBV training in previous studies. Furthermore, the mechanisms underlying the effects of WBV on muscle performance has not been well explored. Therefore, the present research was conducted that comprised two parts, the first and also the main study in this thesis was to investigate the effects of 36 sessions of WBV training on seniors with sacropenia and to compare three different WBV training frequency and duration for the subjects so as to identify the optimal training parameter. Eighty seniors aged 65 years and above with sarcopenia were recruited and randomly assigned into 1 of 4 groups receiving either low frequency with long exposure time (LG: 20Hz and 720s per session), medium frequency with medium exposure time (MG: 40Hz and 360s per session), high frequency with short exposure time (HG: 60Hz and 240s per session) of WBV training or no intervention as control (CG). The WBV training consisted of 36 exercise sessions over a 12-week period. Assessments were conducted at baseline, mid-intervention (6 weeks of WBV), post-intervention (12 weeks of WBV), 6 and 12 weeks after cessation of training. The outcome assessments included ultrasound measurement of vastus medialis for its cross-sectional area (CSA), knee extension isometric strength at 90° of flexion and isokinetic knee extensor peak torque at 60°/s and 180°/s, Timed-up-and-go test (TUG), Five-repetition sit-to-stand test (5STS), knee joint position (KJP), tandem stance, one leg standing (OLS) and 10-meter walk test with self-preferred and maximum speed. Only MG group demonstrated significant increase in isometric knee extension (p=0.017) after 36 sessions of WBV training. Both LG and MG showed significant improvements in isokinetic knee extension at 180°/s (LG: p=0.001; MG: p=0.006), isokinetic knee extension at 60°/s (LG: p=0.041; MG: p=0.016), TUG (LG: p<0.001; MG: p<0.001), 5STS (LG: p=0.038; MG: p=0.001), self-preferred walking speed (LG: p=0.008; MG: p=0.029). Among the three training groups, only MG had significantly better performance than the CG in isokinetic knee extension at 180°/s (p=0.022), TUG (p=0.001), 5STS (p=0.008), self-preferred speed walking speed (p=0.040). For CSA and balance performance, there were no significant group differences after 36 sessions training. No significant differences were found in muscle strength between post-intervention and 12-week follow-up assessments (p>0.05). Compared with baseline, all three training groups had significant improvements in isokinetic knee extension at 180°/s even after 12-week cessation of training (LG: p=0.01; MG: p=0.006; HG: p=0.015). The improvements in TUG and 5STS in LG and MG could not maintained for 12 weeks after training cessation (p<0.05). Only MG had significant difference from CG in isokinetic knee extension at 180°/s and TUG after 12-week cessation of training. After completion of the main study, another study was conducted to investigate the possible mechanism of WBV training for the improvement of muscle performance with the MG training protocol. Ten subjects with sarcopenia were recruited and allocated into either MG WBV (n=5) or control group (n=5). Twitch interpolation test was performed for the quadriceps muscle of the dominant leg before and after a 12-week training programme to investigate the effect of WBV training on the voluntary activation of this muscle so as to explore the possible underlying effect associated with WBV at the neuromotor activation level. After 12 weeks of WBV training, the interpolated muscle twitch ratio of WBV group was increased by 1.33% and the changes of interpolated muscle twitch ratio were significantly different between the two groups (p=0.044). In general, WBV training was effective on improving muscle and physical performance in seniors with sarcopenia. The frequency/time combination of 40Hz and 360s has the best outcome among all other combinations tested in the main study of this thesis. The finding that WBV training would increase voluntary activation of quadriceps in seniors with sarcopenia implies that a possible mechanism of WBV training for muscle improvement would be central drive facilitation.