Aging related co-contraction effects on balance recovery using the ankle strategy
Date
2010
Authors
Mixco, Anthony, author
Reiser, Raoul Frederick, II, advisor
Tracy, Brian L., advisor
Greene, David Paul, committee member
Journal Title
Journal ISSN
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Abstract
Aging typically leads to an increased risk for falls. Fall risk has been associated with, amongst other variables, a decline in muscle strength and power. An accepted model to assess one's ability to recover balance is with a perturbation of quiet stance through the release of a horizontal tether pulling at the waist. PURPOSE: To examine ankle muscle co-contraction levels in young and older adults during static held maximum voluntary contraction (MVC), rate of force development (RFD), as well as prior to and during an induced perturbation. METHODS: 18 healthy adult women (9 young: 22.3+3.3 yrs and 9 older: 75.2+4.2 yrs) with no history of falls or injury performed a minimum of 3 trials each of isometric MVC where force was ramped to and held at maximum and RFD where force was built as quickly as possible from rest for both plantar flexion (PF) and dorsiflexion (DF). The perturbation trials were then performed where they recovered balance using the ankle strategy. Surface electromyography (sEMG) data were analyzed to compare co-contraction activity between groups. RESULTS: Height, body weight, and foot length were similar between groups (p>0.05). After normalizing for height, weight, and foot length, there were no differences between groups for muscle strength characteristics for PF and DF isometric trials (p>0.05). sEMG parameters were normalized using the PF MVC for the gastrocnemius (GAS) and soleus (SOL) and the DF MVC for the tibialis anterior (TA). No sEMG differences were found between groups for PF MVC, PF RFD, and DF RFD for all muscles (p>0.05). DF MVC showed significantly more co-contracting GAS activity for the young (young: 25.8+8.6%, older: 11.8+3.1%), (p=0.001) but not for SOL (young: 37.3+12.2%, older: 34.5+12.8%) or TA activity (young 66.9+9.1, older: 66.31+7.2%), (p>0.05). Perturbation sEMG showed no significant interactions or main effects for GAS and SOL between time and age (p>0.05). TA activity did show a significant interaction (p=0.001). Simple main effects at each time point comparison between the young and older showed significantly more TA activity in the older adults at 300-400ms after load release (young: 23.5+5.8%, older: 38.7+9.4%), (p=0.001) but nowhere else (p>0.098). Additionally the electromechanical delay (EMD) between torque and onset of muscle activity approached significance for the GAS (young: 0.064+0.009%, older: 0.071+0.01%), (p=0.053). CONCLUSIONS: As expected the older adults showed more TA antagonistic co-contraction during balance recovery. Unexpectedly the young adults showed more GAS activity during DF MVC without a significant difference in force output. The approaching significance of GAS EMD also shows evidence of age-related neuromuscular changes taking place. However because of the lack of difference in strength and rate of force development between the two age groups the additional antagonistic torque produced by the older adults may be compromising the balance recovery process. In less physically capable older adults, the differences seen in TA activity and EMD may cause problems in recovering balance from perturbations.
Description
Department Head: Stuart A. Tobet.