Howatson, G., van Someren, K. A., & Hortobagyi, T. (2004). The repeat bout effect following initial low and high volume eccentric exercise. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 2195.

"An initial bout of eccentrically biased exercise protects skeletal muscle against damage in subsequent bouts, but the volume required to elicit protection is unclear. One mechanism that could mediate this protective effect is a shift in motor unit recruitment in the repeat bout, towards motor units that were used to a lesser extent or not at all in the initial bout" (p. S320). This investigation compared markers of muscle damage and surface electromyography (EMG) activity from an initial low volume or high volume bout followed by a subsequent high volume bout of maximal eccentric exercise. Males (N = 16) were assigned to a low volume or high volume group (10 and 45 maximal eccentric contractions of the elbow flexors, respectively). Surface EMG activity was recorded during the first 10 contractions of each bout from the biceps brachii. The damage markers of creatine kinase, soreness rating, and maximum isometric strength were measured before, 48 hours, and 96 hours after the initial exercise and at the same times before and following a subsequent bout of high volume eccentric exercise performed 14 days later.

Soreness rating and maximum isometric strength showed significant group × bout interactions; both soreness rating (69.5%) and maximum isometric strength (13.2%) were attenuated in bout 2 for the high volume group. However, there were no differences between groups in bout 2. Median EMG frequency significantly decreased from the initial bout to the subsequent bout by 9.7%, without differences between groups.

Implication. Both low volume and high volume maximal eccentric exercise produced a similar repeat effect in subsequent high volume bouts. Any changes eliciting a repeat bout effect may be attributed, at least in part, to a neural adaptation in the first 10 maximal eccentric contractions of the initial exercise bout. The reduction in median EMG frequency may indicate a shift in motor unit recruitment that is independent of the volume of the initial exercise bout.

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