Biomechanics of muscular effort: age-related changes.

PURPOSE: The ability of older adults to perform activities of daily living (ADL) declines with age. One possible reason could be that older adults require substantially greater effort than younger adults to perform similar ADL. This study examined the effects of age on the biomechanics of muscular effort in healthy adults during isometric torque production tasks.
METHODS: Thirty healthy adults [15 younger (8 males, 7 females, aged 29.3 +/- 5.53 yr) and 15 older (8 males, 7 females, aged 70.8 +/- 3.6 yr)] participated in this study. After the determination of maximal voluntary contraction (MVC) strength for both isometric elbow flexion and extension tasks using a dynamometer, the participants then produced isometric elbow flexion and extension joint torques that corresponded to effort levels of 1, 3, 5, 7, and 9 on a modified Borg-CR10 scale. The 10 conditions (2 tasks x 5 effort levels) were presented in random order. A three-way repeated-measures ANOVA was used to assess the effects of age, task, and effort level on absolute (N.m) and relative (% MVC) elbow joint torques.
RESULTS: Older adults required significantly greater muscular effort to accomplish equivalent motor task performance as compared with younger adults for effort levels of 3, 5, 7, and 9 (P < 0.001). In addition, older adults demonstrated significantly greater muscular effort scaling error than younger subjects across all effort levels (P < 0.0001).
CONCLUSION: There was an age-related increase in muscular effort during isometric elbow flexion and extension torque production tasks in healthy adults. Errors in muscular effort scaling exist, which increased as a function of both intensity (effort level) of motor task and age.