Skeletal muscle power: a critical determinant of physical functioning in older adults

Abstract

Muscle power declines earlier and more precipitously with advancing age compared with muscle strength. Peak muscle power also has emerged as an important predictor of functional limitations in older adults. Our current working hypothesis is focused on examining lower extremity muscle power as a more discriminant variable for understanding the relationships between impairments, functional limitations, and resultant disability with aging.

Figure 1

Power driven pathway to age-associated disability. [Adapted from (35). Copyright © 1994 Elsevier. Used with permission.]

Figure 2

Absolute power (Watts, A) and specific power (normalized to anterior mid-thigh muscle cross sectional area) (Watts per cm², B) plotted against movement velocity in middle-aged healthy (mean ± SD age: 47.2 ± 5 yrs), older healthy (74 ± 4 yrs) and older mobility-limited participants (78.1 ± 5 yrs). Testing was conducted using a Cybex-II dynamometer. Five consecutive maximal isokinetic (constant velocity) knee extensions were performed at 60, 90, 180, and 240 degrees second, with participants instructed to kick out as fast and hard as possible. Each testing condition was separated by at least 1 minute of rest. A significant group × velocity interaction was indicated for both power variables with all groups significantly different. Post hoc testing revealed: *older mobility-limited was less than middle-aged healthy adults and older healthy adults; †power has increased from the previous (slower) velocity in middle-aged healthy and older healthy but not in older mobility- limited; and ‡power has increased from the previous (slower) velocity in middle-aged healthy but not in older healthy or older mobility-limited. Older mobility-limited showed no difference is absolute or specific power between contraction velocities (60–90, or between 90, 180 and 240 degrees per second) indicating a plateau in the ability to produce power at faster speeds. (Reprinted from (13).Copyright © 2010 Oxford University Press. Used with permission.)

Figure 3

Absolute activation (thick black lines) and activation corrected for subcutaneous adipose* (thin gray lines provided for agonist muscles only) plotted against movement velocity. Activation was assessed from quadriceps and hamstrings muscles using surface electromyography (EMG). Agonist activation amplitude for each muscle was higher in middle-aged healthy adults and older healthy adults compared with older adults with mobility limitation. Furthermore, both middle-aged healthy and older healthy demonstrated significant positive associations between activation amplitude and velocity, whereas older mobility-limited did not. *EMG data were corrected because of the recognized signal attenuation caused by subcutaneous adipose tissue. (Reprinted from (13).Copyright © 2010 Oxford University Press. Used with permission.)