MONITORING HIGH-INTENSITY ENDURANCE TRAINING USING NEUROMUSCULAR EXCITABILITY TO RECOGNIZE OVERTRAINING

The minimal rectangular current pulse that produces a single contracti on of reference muscles at different pulse durations has been recommen ded as a marker of the neuromuscular excitability (NME) of skeletal mu scles. NME is improved in well-trained, nonfatigued endurance athletes and deteriorates after prolonged heavy exercise and high-volume overt raining. The hypothesis was tested that a deterioration in NME also in dicates an early stage in the overtraining process during high-intensi ty endurance training. Six subjects participated for 40-60 min per day in a 6-week, 6-days-per-week, intensive, steady-state and interval tr aining program using a cycle ergometer. Training was stopped each day on volitional exhaustion. On day 7 of each week training was of low in tensity for about 30-40 min. Submaximum and maximum power output were significantly increased after 3 weeks, but there was no further improv ement, rather a deterioration after week 6 compared to week 3. Even af ter 2 weeks of regeneration no supercompensation was evident, rather a decrease in maximum power output. NME was slightly improved after 3 w eeks, but deteriorated after 6 weeks, and was again normalized after 2 weeks of regeneration. The discrepancy between normalization of NME a nd still-deteriorated performance ability after 2 weeks of regeneratio n reflects additional significant, and probably central mechanisms tha t explain persistent performance incompetence. Deterioration in NME ma y indicate an early stage in the overtraining process during high-volu me as well as high-intensity endurance overtraining, but normalization does not necessarily indicate sufficient regeneration.