DOES THE CONTRACTION HISTORY OF THE MUSCLE DICTATE CHANGES IN STRENGTH FOLLOWING RESISTANCE TRAINING?

Within-subject training models, whereby researchers apply an exercise condition to one limb, and a separate exercise condition to the opposing limb, have become routine amongst the exercise literature. However, no study has directly tested whether exercising one limb with a high-load condition will influence strength adaptations within the opposing limb, even when the opposite limb is training. Furthermore, muscle post-activation performance enhancement (PAPE) is representing local level changes, however, more research is warranted to understand if this can be differentially impacted with different types (e.g. low load vs. high load) of resistance training. The purpose of this study was to determine if unilateral high-load training influences strength adaptations within the contralateral limb. A secondary purpose was to discern whether PAPE could be increased with resistance training. 116 participants were randomized to one of three intervention groups, and completed 18 training sessions involving isotonic elbow flexion exercise. Group 1 trained their dominant arm only, with a one-repetition maximum (1RM) test (maximum five attempts), followed by four sets of traditional exercise at an 8-12 RM. Group 2 completed the same training as Group 1 in their dominant arm, whilst the non-dominant arm completed four sets of low-load exercise (30-40 RM). Group 3 trained their non-dominant arm only, performing the same low-load exercise as Group 2. Participants were compared for changes in muscle thickness, isotonic elbow flexion 1RM, and postactivation performance enhancement (PAPE). Groups 1 (Δ 1.5 kg) and 2 (Δ1.1 kg) presented the greatest changes in non-dominant strength, as compared to Group 3 (Δ 0.3 kg). Only the arms being directly trained saw changes in muscle thickness, when compared to the untrained limbs. There were no differences amongst groups for changes in PAPE. Unilateral high-load training appears to influence strength changes in the contralateral arm, despite the contralateral arm training with a low-load exercise. Results of this study have broader implications for future research, and suggest that within-subject training models cannot be used when the primary outcome is strength changes