Unilateral high-load resistance training influences strength changes in the contralateral arm undergoing low-load training

Objectives: Within-subject training models have become common within the exercise literature. However, it is currently unknown if training one arm with a high load would impact muscle size and strength of the opposing arm training with a low load. Design: Parallel group. Methods: 116 participants were randomized to one of three groups that completed 6-weeks (18 sessions) of elbow flexion exercise. Group 1 trained their dominant arm only, beginning with a one-repetition maximum test (& LE;5 attempts), followed by four sets of exercise using a weight equivalent to 8-12 repetition maximum. Group 2 completed the same training as Group 1 in their dominant arm, while the non-dominant arm completed four sets of low-load exercise (30-40 repetition maximum). Group 3 trained their non-dominant arm only, per-forming the same low-load exercise as Group 2. Participants were compared for changes in muscle thickness and elbow flexion one-repetition maximum. Results: The greatest changes in non-dominant strength were present in Groups 1 (& UDelta; 1.5 kg; untrained arm) and 2 (& UDelta;1.1 kg; low-load arm with high load on opposite arm), compared to Group 3 (& UDelta; 0.3 kg; low-load only). Only the arms being directly trained observed changes in muscle thickness (& AP;& UDelta; 0.25 cm depending on site). Conclusions: Within-subject training models are potentially problematic when investigating changes in strength (though not muscle growth). This is based on the finding that the untrained limb of Group 1 saw similar changes in strength as the non-dominant limb of Group 2 which were both greater than the low-load training limb of Group 3. & COPY; 2023 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.