Neuromuscular and functional adaptations to whole body vibration exercise in older adults

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The ageing process is associated with sarcopema: a reduction in muscle mass, strength and power. Sarcopenia is responsible for diminished physical performance; it affects the ability to perform activities of daily living and can severely impact quality of life in older age. There is potentially no age group that can benefit more from interventions to combat reduced muscle strength and power than an older population. Whole body vibration (WBV) is a relatively new exercise intervention. WBV is suggested to improve strength and power by stimulating the neuromuscular system and inducing reflex muscle contractions. The potential for WBV to be used as a strength training intervention for an older population was the rationale behind this thesis. Study one was an investigation of the effects of eight weeks WBV on a range of physical perfonnance measures in a healthy, older population. Forty three, older adults (73.5 ± 4.5 yr, 168.2 ± 10.5 cm, 74.5 ± 11.1 kg) were divided into three groups: 15 to a WBV group (VIB), 13 to an exercise without vibration group (EX) and 15 into a control group (CONT). The VIB and EX group interventions consisted of three sessions per week for eight weeks. Outcome measures included isokinetic flexor and extensor strength of the hip, knee and ankle, one-legged postural steadiness (OLPS), sit-to-stand performance (STS), fast walk time and stair mobility. Following the eight week intervention, the VIB group significantly improved OLPS compared to the EX and CONT groups (p<0.05). The improvements in OLPS were significantly affected by baseline values, with the largest changes evident for VIB participants with a poorer initial score (p<0.01). WBV exercise can improve OLPS in a healthy, older population. As improvements in OLPS were related to baseline values, WBV as an intervention would appear to serve the most benefit for those that exhibit diminished postural control. The VIB group significantly improved ankle plantar flexor strength compared to the EX and CONT group (18.2%, 5.0%, 0.9%) (p<0.05). The VIB and EX groups both significantly improved knee extension strength compared to the CONT (8.1 %, 7.2%, - 2.0%) (p<0.05). There were no effects for hip flexor or extensor strength. The VIB and EX groups both showed improved STS (12.4%, 10.2%) and Sm fast walk (3.0%, 3.7%) compared to the control (p<0.05). There were no effects for stair mobility performance. While WBV exercise can be considered a plantar flexor strength training intervention, it appears to have a disproportional effect on lower limb strength. WB V did not facilitate knee extensor strength or physical performance measures to a greater degree than the same exercise program without vibration. The comparable change in physical perfonnance measures between the VIB and EX groups appears linked to similar gains in knee extensor strength. Further, these similar knee extensor strength improvements appears linked to the same body weight squats performed by both the VIB and EX groups. To explore the disproportional change in lower limb strength found in study one, study two was designed to investigate the neuromuscular activation of the ankle, knee and hip flexors and extensors during WBV. Ten healthy, older male participants (70.4 ± 4.9 yr, 176.9 ± 7.8 cm, 78.6 ± 12.0 kg) completed a number of static exercises with and without WBV. Activation of the soleus, gastrocnemius, tibialis anterior, vastus medialis, rectus femoris, biceps femoris, iliopsoas and gluteus maximus were recorded unilaterally with electromyography (EMG). EMG amplitude was normalised and analysed with respect to each individual's maximum isometric strength values. The absolute increases in EMG with vibration, above the non-vibration condition, were compared between muscle groups and exercise conditions. The increase in neuromuscular activity with WBV was significantly larger in the soleus and gastrocnemius than muscles higher up the leg (p<0.05). Furthermore, the increase in gastrocnemius neuromuscular activity was greatest when participants maintained a heel raise position. It appears that WBV should be prescribed as an exercise intervention that intends to specifically train the triceps surae musculature. The results of study one and two suggested WBV be considered a localised strength training intervention for older individuals which predominately targeted the plantar flexors. The aim of study three was to examine the efficacy of WBV for a frail, elderly population; to validate plantar flexor strength improvement with WBV and examine the neuromuscular mechanisms associated with this adaptation. Seventeen frail, older participants (88.2 ± 3.6 yr, 166.8 ± 8.2 cm, 71.7 ± 11.4 kg) were divided into two groups: ten to a WBV group (VIB) and seven to a control group (CONT). The VIB group undertook WBV three times per week for four weeks. Outcome measures included isometric and isokinetic plantar flexor strength, single leg balance performance and EMG of the gastrocnemius. The EMG signal was analysed for amplitude and median power frequency. EMG amplitude was normalised with respect to each individual's maximum isometric strength values. WBV had no effects on single leg balance performance in a frail , older population. This result is in contrast to study one that found significant improvements in OLPS in a population of healthy, older adults. In contrast to study one participants, the frail older adults in study three were unable to exercise on the WBV platform without firmly grasping the handlebars for support. The difficulty maintaining balance whilst undertaking WBV exercise is suggested to be a mediating factor behind the improvements in balance observed in study one but not three. Following the WBV intervention, the VIB group significantly improved isometric (40.5%) and isokinetic (32.4%) plantar flexor strength compared to the CONT group (1.5%, 2.9% respectively) group (p<0.05). The WBV group displayed a significant 32.3% increase and a 8.3% decrease in right medial gastrocnemius EMG peak amplitude and EMG median power frequency respectively during isometric plantar flexion (p<0.05). WBV can be considered an effective training intervention to improve plantar flexor strength in frail, older adults. It is speculated that increased plantar flexor strength with WBV exercise be explained at least in part by an improvement in motor unit synchronisation and efficiency.
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