Post-contraction potentiation can react inversely to post-activation potentiation depending on the test contraction force

The surface electromyographic (EMG) activity of the biceps brachii during weak elbow flexion reportedly in-creases immediately after strong elbow flexion, even during the exertion of a given force. This phenomenon is called post-contraction potentiation (EMG-PCP). However, the effects of test contraction intensity (TCI) on EMG-PCP remain unclear. This study evaluated PCP levels at various TCI values. Sixteen healthy participants were asked to perform a force matching task (2%, 10%, or 20% of the maximum voluntary contraction [MVC]) before (Test 1) and after (Test 2) a conditioning contraction (50% of MVC). With a 2% TCI, the EMG amplitude was higher in Test 2 than in Test 1. With a 20% TCI, the EMG amplitude was lower in Test 2 than in Test 1. Furthermore, EMG spectral analyses showed that the alpha-and beta-band power ratios in Test 2 were enhanced by 2% TCI compared with Test 1. These findings suggest that TCI is crucial in determining the EMG-force relationship immediately after a brief intensive contraction.