Knee extensor stiffness and functional performance

Abstract

Objective To determine the reliability of a new method to measure the stiffness of the knee extensors and thereafter establish the relationship between knee extensor stiffness and, jump and running performance. Setting A professional rugby union football club and a university laboratory. Participants Thirty semi-elite male rugby union players. Main outcome measures The stiffness of the knee extensors across loads ranging from 30 to 70% maximal voluntary isometric contraction, 20 m sprint, maximal squat strength, countermovement-jump and drop-jump performance was assessed. Results Within trial variation (coefficient of variation—range 5.41–7.45%) for all five loads (30, 40, 50, 60 and 70%) and test–retest reliability (intra-class correlation coefficients—range 0.92–0.96) were deemed acceptable. Knee extensor stiffness was found to have no significant relationship ( P>0.05) to any of the functional performance measures ( r=−0.160–0.172). Conclusion It was concluded that the new protocol to assess the stiffness of the knee extensors was reliable, however the relationship between knee extensor stiffness and measures of strength, power and speed was weak and non-significant.