STEADINESS DURING ECCENTRIC, CONCENTRIC, AND ISOMETRIC QUADRICEPS CONTRACTIONS

8 Steadiness of upper extremity muscles has been investigated in young and old humans and in subjects with motor deficits (Grabiner and R. Enoka, ESSR 23:65, 1995). Little attention has been devoted to steadiness in lower extremity muscles. We examined steadiness in the quadriceps muscle at two levels of target force in healthy sedentary young subjects. Steadiness was assessed as variability in force with larger variability indicating lower steadiness. On two separate days, 4 men and 2 women (age 22 yr.) performed 10 trials each of isometric, and 15 °/s concentric and eccentric contractions on a Kin-Com dynamometer. Subjects tried to match 25 and 50 N target forces. Table 1 (mean ±SD) shows the significant interaction (F = 5.4, p = 0.0256) for steadiness (force variability) at the two force levels and the three contraction modes and the results of the Tukey post hoc. Steadiness was greater (and force variability lower) at 50 N than at 25 N under concentric and eccentric (a) but it was greater at 50 N than at 25 N under isometric conditions (b). Steadiness was the highest during isometric, followed by concentric (c) and eccentric (d) contraction. These data agree with previous findings on upper extremity muscles that steadiness is the least during eccentric contractions. But unlike prior studies, we found greater steadiness at higher and not at the lower target force.Table 1: Steadiness (force variability) data.Supported in part by UNC Inst. on Aging (P.D.) and NICHD (T.H.)