Moment-angle relations after specific exercise

This study examined the amount and time-course of shifts in the moment-knee angle relation of the quadriceps (QF) and hamstring (HAM) muscles in response to different length-restricted strength training regimens. Thirty-two athletes were divided into three different training groups (G1-3): G1 performed isometric training at knee joint angles corresponding to long muscle-tendon unit (MTU) length for QF and HAM; G2 conducted concentric-eccentric contraction cycles that were restricted to a knee joint range of motion corresponding to predominantly long MTU length for QF and HAM; G3 combined the protocols of G1 and G2. Moment-knee angle and EMG-knee angle relations of QF and HAM were measured on five different occasions: two times before, after five and eight weeks of training and four weeks post training. Moments and EMG-data of each subject were normalized to the largest value produced at any knee joint position [% Max.]. Obtained by curve fitting, the optimal knee joint angle for QF moment production was significantly (P<0.05) shifted to longer MTU length in G1 and G3 after 5 weeks of training and in G2 after 8 weeks of training. Contrary, no significant shifts were detected for HAM. Our data suggest that the predominant MTU length during loading is a major trigger for human force-length adaptations.