Daily muscle activity and quiescence in non-frail, pre-frail, and frail older women.

Reduced muscle mass and strength are likely fundamental components of frailty. The purpose of this study was to measure daily muscle activity and quiescence in non-frail, pre-frail, and frail older women using portable electromyography (EMG). Thirty-three community-dwelling older Greek women were categorized as non-frail (n=10, 74±4years), pre-frail (n=11, 75±4years), and frail (n=12, 81±6years) based upon the frailty phenotype. Surface EMG over a 9-hour typical day was recorded from the biceps brachii, triceps brachii, vastus lateralis, and biceps femoris of the dominant side. Burst and gap analysis was used to quantify muscle activity and quiescence. The total duration of the muscles that were active (2.5h) and quiescent (4h) did not differ across frailty groups. However, the number of bursts was 28% fewer and the mean burst duration was 26% longer in frail women compared with the non-frail women. In addition, muscle activity was greater in the arm muscles than the thigh muscles across all groups (e.g. ~60% greater burst percentage). Burst number and duration indicate that muscle activity differs across stages of frailty in older women and is greater in the upper compared with lower limbs.