Variability of concentric angle-specific isokinetic torque and impulse assessments of the knee extensors

Abstract

Objective: Length-tension relationships are widely reported in research, rehabilitation and performance settings; however, several isometric contractions at numerous angles are needed to understand these muscular outputs. Perhaps a more efficient way to determine torque-angle characteristics is via isokinetic dynamometry; however, little is known about the variability of isokinetic measurements besides peak torque and optimal angle. This paper examines the variability of angle-specific isokinetic torque and impulse measures. Approach: Three sessions of concentric (60°·s−1) knee extensions were performed by both limbs of 32 participants. Assessments were repeated on three occasions, separated by 5–8 d. To quantify variability, the standardized typical error of measurement (TEM) was doubled and thresholds of 0.2–0.6 (small), 0.6–1.2 (moderate), 1.2–2.0 (large), 2.0–4.0 (very large) and >4.0 (extremely large) were applied. Additionally, variability was deemed large when the intraclass correlation coefficient (ICC) was <0.67 and coefficient of variation (CV) > 10%; moderate when ICC > 0.67 or CV < 10% (but not both); and small when both ICC > 0.67 and CV < 10%. Main results: Isokinetic torque and angular impulse show small to medium variability (ICC = 0.75–0.96, CV = 6.4%–15.3%, TEM = 0.25–0.53) across all but the longest (100°) and shortest (10°) muscle lengths evaluated. However, moderate to large variability was found for the optimal angle (ICC = 0.58–0.64, CV = 7.3%–8%, TEM = 0.76–0.86), and torque and impulse at the beginning and end of the range of motion (ICC = 0.57–0.85, CV = 11–42.9%, TEM = 0.40–0.89). Intersession variability of isokinetic torque and impulse were small to moderate at medium (90–20°) joint angles. Significance: Researchers and practitioners can examine the muscle torque-angle relationship and activity-specific torque outputs within these ranges, without resorting to more strenuous and time-consuming isometric evaluations.