The relationship between bilateral differences of knee flexor and extensor isokinetic strength and multi-directional speed

Abstract

This study analyzed relationships between bilateral concentric (60 ◦ /s, 180 ◦ /s, 240 ◦ /s) and eccentric (30 ◦ /s) knee extensor and flexor strength differences, and linear (40-meter sprint), and change-of-direction (T-test) speed in 16 male team sport athletes. It was hypothesized that lower between-leg strength differences would be associated with faster speeds. Subjects were divided into faster and slower groups based on total time; a one-way analysis of variance (p 0.05) determined bilateral torque and work differences that distinguished the groups. All data was combined to correlate (p 0.05) torque and work differences with sprint times. The faster group exhibited greater differences in concentric knee extensor torque at 240 ◦ /s (faster = 11.74 ± 8.65%; slower = 4.13 ± 4.34%), and smaller differences in eccentric knee flexor torque (faster = 5.64 ± 4.10%; slower = 12.41 ± 7.55%) and work (faster = 6.36 ± 6.65%; slower = 15.55 ± 6.05%). Negative correlations were found between concentric 180 ◦ /s and 240 ◦ /s knee extensor torque differences and sprint times; however, speed was not negatively affected. Positive correlations existed between eccentric knee flexor work differences and sprint times. Eccentric strength differences negatively impacted multi-directional speed, as balanced eccentric strength is necessary for effective sprinting, deceleration, and changing direction.