Single‐leg hop testing following fatiguing exercise: reliability and biomechanical analysis

A fatiguing exercise protocol was combined with single‐leg hop testing to improve the possibilities of evaluating the effects of training or rehabilitation interventions. In the first test–retest experiment, 11 healthy male subjects performed two trials of single‐leg hops under three different test conditions: non‐fatigued and following fatiguing exercise, which consisted of unilateral weight machine knee extensions at 80% and 50%, respectively, of 1 repetition maximum (1 RM) strength. Intraclass correlation coefficients ranged from 0.75 to 0.98 for different hop test conditions, indicating that all tests were reliable. For the second experiment, eight healthy male subjects performed the fatiguing exercise protocol to investigate how fatigue influences lower‐extremity joint kinematics and kinetics during single‐leg hops. Hip, knee and ankle joint angles, moments and powers, as well as ground‐reaction forces were recorded with a six‐camera, motion‐capture system and a force platform. Recovery of hop performance following the fatiguing exercise was also measured. During the take‐off for the single‐leg hops, hip and knee flexion angles, generated powers for the knee and ankle joints, and ground‐reaction forces decreased for the fatigued hop conditions compared with the non‐fatigued condition ( P <0.05). Compared with landing during the non‐fatigued condition, hip moments and ground‐reaction forces were lower for the fatigued hop conditions ( P <0.05). The negative joint power was two to three times greater for the knee than for the hip and five to 10 times greater for the knee than for the ankle during landing for all test conditions ( P <0.05). Most measured variables had recovered three minutes post‐exercise. It is concluded that the fatiguing exercise protocol combined with single‐leg hop testing was a reliable method for investigating functional performance under fatigued test conditions. Further, subjects utilized an adapted hop strategy, which employed less hip and knee flexion and generated powers for the knee and ankle joints during take‐off, and less hip joint moments during landing under fatigued conditions. The large negative power values observed at the knee joint during the landing phase of the single‐leg hop, during which the quadriceps muscle activates eccentrically, indicate that not only hop distance but also the ability to perform successful landings should be investigated when assessing dynamic knee function.