Age-related differences in temporal scaling of postural EMG activity

Electromyographical (EMG) burst onset times for postural muscles were compared in young and elderly male and female subjects performing a forceful abrupt pull with the right arm against a load cell apparatus while standing. EMG activity was collected via surface electrodes from the posterior deltoid, and right and left hamstring and quadriceps muscles. Pulls were performed at varying force levels from 100% to approximately 50% of a maximum effort. Regression equations were developed for each postural muscle for each group, using force production values as the independent variable, and postural muscle onset latencies (relative to deltoid onset) as the dependent variable. Regression slopes for postural muscles of elderly subjects ranged from 0.59 to 0.33, while slopes for the young subjects ranged from 0.72 to 0.63. Less elevated slopes for the elderly may indicate a reduced ability to temporally scale postural muscle onset latencies to variations in the force of the upper-limb task; a reduction in this ability may constitute a possible contributing factor to instability in the elderly.