Aging and the Effects of Power Training and Neuromuscular Enhancement on Standing Balance

Abstract

Background. Aging brings about impairments in hip abductor-adductor (AB-AD) neuromuscular performance and medio-lateral balance control. Power training (PT) has been used as an alternative to strength training that leads to further neuromuscular performance improvements. Furthermore, transcranial direct current stimulation (tDCS) can acutely increase force output. Aim. This dissertation investigated how aging, hip AB-AD power training (PT) and transcranial direct current stimulation (tDCS) affect maximal hip AB-AD neuromuscular performance and medio-lateral balance control during the weight transfer of induced lateral steps and forward/lateral voluntary stepping. Methods. Participants performed a hip AB-AD isometric maximal voluntary contractions (IMVC) task, an induced lateral stepping task at different initial limb pre-loads and forward/lateral voluntary stepping. PT program consisted of 8 weeks of hip AB-AD exercises focusing on maximal speed of execution. Anodal and cathodal tDCS were used to elicit acute neuromuscular improvements in the hip AB-AD. Results. Aging reduces maximal isometric hip AB-AD neuromuscular performance (31-67%, p<0.05). During induced lateral stepping, aging decreased hip AB-AD rate of neuromuscular activation (RActv) (60-109%, p<0.05) and delayed the weight transfer phase (30-78ms, p<0.05). Consequently, older individuals increased their vertical RFD (70-177%, p<0.05) and hip muscular output (31-74%, p<0.05), but still had lower balance performance than younger adults. PT significantly improved maximal isometric hip AB-AD neuromuscular performance (14-81%%, p<0.05) and increased incidence of single lateral balance recovery steps (43%, p<0.05), through increases hip AB torque (49-61%, p<0.05), AB power (21-54%, p<0.05) and AB-AD RActv (17-62%, p<0.05) during the weight transfer of the lateral balance stepping task. PT also improved voluntary stepping onset latencies (13-28%, p<0.05). Lastly, tDCS modulated maximal hip AB peak torque (8-12%, p<0.05) and anodal tDCS enhanced hip AB maximal RTD (28-55%, p<0.05). Conclusions. Aging impairs hip maximal neuromuscular performance. Consequently, medio-lateral balance recovery becomes impaired as individuals operate closer to their maximum capabilities. Furthermore, PT is able to increase older adults' hip maximal neuromuscular performance, which allows them to increase their hip AB-AD neuromuscular output during medio-lateral balance recovery and improve balance recovery. Lastly, tDCS seems to be a viable alternative to acutely modulate hip AB performance having strong implications for medio-lateral balance recovery.