Upper limb and trunk muscle activation during an unexpected descent on the outstretched hands in young and older women

Abstract

Falling on the outstretched hands (FOOSH), a protective mechanism to arrest the body and avoid injury, requires upper limb and trunk motor control for effective body descent. The purpose of this study was to investigate muscle activity during three phases of an unexpected FOOSH in healthy older and younger women. Twenty young (mean age 22.9yrs, SD±3.7) and 20 older females (mean age 68.1yrs, SD±5.0) performed five trials of unexpected FOOSHs. Surface electromyography (EMG) determined muscle activations for left shoulder girdle, elbow and abdominal muscles during an unexpected FOOSH. Root mean squared EMG data were calculated during three phases: (1) baseline (BL; 500msprior to release), (2) the preparatory phase (PRE; time between release and impact) (mean 257±37ms) and post-impact (POST; 200msafter impact). A mixed MANOVA determined differences between phases and age groups. There was a significant multivariate interaction effect of age and time phase on muscle activity (p=0.001). Younger women had significantly higher internal oblique/transversus abdominus activity during PRE (p=0.006) as well as variations in muscle activity of shoulder girdle and elbow muscles. The age differences observed may lead to poorer preliminary trunk activation and greater arm bracing in older women, potentially increasing risk of fallrelated injury.