Changes in Motor Unit Estimates with Aging

Abstract

Elderly persons usually exhibit some degree of muscle atrophy, together with a reduction in voluntary strength, but there is still argument concerning the nature of the cellular events involved. This issue was reexamined by estimating the numbers and relative sizes of motor units in three limb muscles, using a fully automated system (Galea et al., 1993). In 79 healthy volunteers aged 20-98 years, estimations of motor unit numbers were performed on the thenar, biceps brachii, and extensor digitorum brevis muscles. Motor unit populations were noted to decrease significantly with age in the distal muscles but appeared to remain constant in the biceps. The excitable muscle fiber mass, as reflected in the peak-to-peak amplitude and area of the maximum M-wave, was diminished in all three muscles. Although the area of the average motor unit action potential was not significantly different between groups, the ratio of this potential to the M-wave area increased with increasing age. The results suggest that muscle deterioration in the elderly is due to a combination of changes in the muscle fibers and in their nerve supply and that the extent may differ between proximal and distal muscles.

Effects of Vibration Exercise on Muscle Performance and Mobility in an Older Population

“…This muscle group exhibits a significant decline in strength with the aging process (Simoneau, Martin, & Van Hoecke, 2005). In older adults, distal muscle groups are also considered more susceptible to the aging-related motor-unit loss then more proximal muscles (Galea, 1996). Because ankle-plantar-flexion strength plays an important role in mobility and balance in the older population (Kerrigan, Todd, Della Croce, Lipsitz, & Collins, 1998;Onambele, Narici, & Maganaris, 2006;Suzuki, Bean, & Fielding, 2001), WBV might serve as a supplement to other training methods in mediating functional decline.…”

Fatigue in older adults: an early indicator of the aging process?

“…Loss of muscle mass will theoretically affect oxygen demand and perfusion (oxygen delivery) during muscle contractions at the same relative force levels. In addition to muscle mass, maximal voluntary muscle strength is determined by neural drive from the motor cortex to muscles (88). Maximal voluntary muscle strength is thus an indicator of the functioning of both neural and muscular systems (84).…”

Contributions of Spatial Working Memory to Visuomotor Learning

“…Studies investigating the effects of age on visuomotor adaptation have had mixed results: some groups have reported age-related impairments Fernandez-Ruiz et al 2000;) while others have not . The cause of these deficits is unclear as age-related declines in motor (Booth et al, 1994;Galea, 1996;, sensory Lindenberger & Baltes, 1994), or cognitive function could explain these differences.…”