Motor Output Variability during Isometric, Concentric, and Eccentric Contractions in Young and Old Adults

Rapid eccentric contractions of the quadriceps have been shown to produce a more variable motor outcome than isometric and concentric contractions (Christou & Carlton, 1999, 2000). These findings provide additional support to the hypothesis that the central nervous system may control gradation of muscle force differently for eccentric contractions (Enoka, 1996). Several studies suggest that when old adults perform isometric or slow anisometric contractions they produce more variable movements compared with young adults (Laidlaw et al., 2000). These differences between young and old adults as a function of contraction type, however, have not been examined during rapid tasks. The aim of this study was to compare the ability of young and old adults to control motor output during rapid isometric, concentric and eccentric contractions of the knee extensor muscle group.