THE STEADINESS OF ISOMETRIC CONTRACTIONS IS SIMILAR BETWEEN UPPER AND LOWER EXTREMITY MUSCLE GROUPS

Abstract

The magnitude of fluctuations in force, acceleration, and position can differ across muscle groups based on data from different studies, but a comparison of different muscle groups within the same subjects has not been performed. Ten young (22 ± 3 yrs) and 10 old (72 ± 4 yrs) healthy, sedentary men underwent measurements of maximum voluntary isometric contraction (MVC) force (N), 1-RM load (kg), and steadiness during isometric, concentric, and eccentric contractions with the first dorsal interosseus (FDI), elbow flexor (EF), and knee extensor (KE) muscles. Steadiness during isometric contractions was assessed at target forces of 2.5, 5, 10, 30, and 50% MVC and quantified as the coefficient of variation (CV) for force. The standard deviation (SD) of acceleration was quantified during concentric and eccentric contractions with 5, 10, 30, or 50% 1-RM. 1-RM load, but not MVC force, was lower for all three muscles of the old men compared with the young men. There were significant positive correlations in the CV for force between the EF and KE (r = 0.5 – 0.7) at the 5%, 30%, and 50% MVC forces, and between the EF and FDI at 5% and 10% MVC (r = 0.6–0.8), but not between the KE and FDI. In contrast, there were no significant correlations between any of the three muscle groups for steadiness during anisometric contractions. There were no consistent and significant differences in these correlations between young and old men. These findings suggest that the ability to perform a steady contraction is similar between some muscles during isometric contractions but not during anisometric contractions. Supported by NIH AG13929 to RME and F32 AG05878 to BLT