Effect of Age, Elbow Muscle Co-Contraction Level, and Elbow Moment Loading Charachteristics on Elbow Angle Positional Variability in Postural Tasks.

Biomechanics;Muscle Activation;Steadiness;Positional Variability;Aging;Activities of Daily Living;Biomedical Engineering;Mechanical Engineering;Engineering;Mechanical Engineering

Gordon, Mark T.Sienko, Kathleen Helen ;

University of Michigan

关键词: Biomechanics;    Muscle Activation;    Steadiness;    Positional Variability;    Aging;    Activities of Daily Living;    Biomedical Engineering;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/91474/mtgordon_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Hand positional variability during a task confounds many activities of daily living, such as inserting a key into a lock, pouring hot water into a cup, and eating with a spoon. Current dogma suggests that older adults use increased co-contraction to attenuate hand positional variability; however, this has not been proven. This thesis proposes that elbow muscle co-contraction significantly affects elbow angle positional variability (PV), which affects hand positional variability, and that older adults can reduce their PV by decreasing their co-contraction level.Variable muscle stiffness was incorporated into the Signal Dependent Noise Theory to model the effect of elbow muscle co-contraction on predicted PV during a quasistatic elbow flexion task. The results demonstrated an optimal level of co-contraction that minimized the positional variability for both variable and constant loading paradigms.The first experiment tested the effect of greater than natural elbow muscle co-contraction levels on PV. Fourteen younger and 14 older healthy adults resisted both constant and variable external elbow extension moments while co-contracting at different levels. Increasing co-contraction was found to increase positional variability for both younger and older adults (p < 0.005). Older adults naturally co-contracted at higher levels and had lower positional variability than younger adults (p < 0.005).The second experiment tested the effect of below-natural elbow muscle co-contraction levels on PV in 14 younger and 14 older healthy adults. The effect of age was not significant in predicting positional variability at the lowered co-contraction level.In the third experiment, 12 younger and 14 older healthy adults poured water through different sized container openings. Older subjects co-contracted at higher levels and had lower PV than younger adults. While co-contraction increased with decreasing target size, increased co-contraction within a pouring target size increased PV (p < 0.05) and decreased pouring accuracy (p < 0.001).We conclude that increasing elbow muscle co-contraction increases PV and hinders the performance of tasks, such as pouring, that require low positional variability. This counters the current belief that high co-contraction levels are beneficial for task performance, and suggests that people who struggle with these tasks may benefit from reduced co-contraction.