Supernormal Conduction Velocity in Human Muscle 29 LONG-LASTING SUPERNORMAL CONDUCTION VELOCITY AFTER SUSTAINED MAXIMAL ISOMETRIC CONTRACTION IN HUMAN MUSCLE

We studied muscle fatigue and recovery on healthy males by means of surface and invasive EMG, on biceps brachii and brachioradialis muscle. Fatigue was induced by 1 min of maximal voluntary contraction (MVC), recovery was studied during 60 min (surface EMG) and 15 min (invasive EMG). The main finding was a long-lasting 'supernormal' muscle fiber conduction velocity (MFCV) during recovery. After a normalization phase of 5 minutes, the MFCV continued to increase reaching a steady state at 'supernormal' values after 10-12 min. Mean MFCV increase at 20% MVC after 15 min recovery 0.58 m.s-1 (12%). The changes in median power frequency paralleled the MFCV increase. Post fatigue integrated EMG (IEMG) values were increased at all contraction levels. We suggest that this IEMG increase is mainly a result of the MFCV increase. In the invasive experimental setup we confirmed the MFCV changes. The relative increase in fastest and slowest fibers indicates an equal effect on type I and II fiber types. A possible explanation is muscle fiber swelling, in combination with altered membrane properties.