Knee flexion and extension muscular force steadiness in young adults: sex differences and test-retest reliability

Knee flexion and extension muscular force plays an important role in athletic performance as well as joint stability. Generally, women exhibit weaker peak force than men even after the force is normalized to their body weight. However, it is inconclusive whether there are sex differences in force steadiness (ability to hold submaximal muscular force over a period of time). Twenty-five healthy young subjects completed the maximal voluntary isometric contractions (MVIC) for knee flexion and extension; then, they were asked to hold 10%, 25%, 35%, and 50% MVIC values (visible in monitor) for 10 seconds. Average force and standard deviation in the middle 8 seconds was used to calculate coefficient of variation (CoV). Fifteen subjects returned for the second aim: test-retest reliability. Results revealed no sex differences in force steadiness (P > 0.05). Testing procedures had moderate test-retest reliability (Intraclass Correlation Coefficient: ICC = 0.447 – 0.741).