Hakkinen, J. J., Kraemer, W. J., & Gorostiaga, E. M. (2009). Neuromuscular and metabolic fatigue with the same absolute and relative intensity after strength training. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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This study examined the effects of heavy resistance training on a dynamic exercise-induced fatigue task (5 x 10 RM leg-press) after two loading protocols with the same relative intensity (%)(5 x 10 RMRel) and the same absolute load (kg)(5 x 10 RMAbs) as in pre-training in men (N = 12). Maximum strength and muscle power, surface EMG changes (amplitude and spectral indices of muscle fatigue), and the metabolic responses of blood lactate and ammonia concentrations were measured before and after exercise.

After short-term heavy resistance training, when the relative intensity of the fatiguing dynamic protocol was kept the same: 1) the magnitude of exercise-induced loss in maximal strength was greater than that observed before training, 2) the peak power lost after 5 x 10 RMRel (58-62%, before and after training) was greater than the corresponding exercise-induced decline observed in maximal dynamic (23-34%) and isometric strength (12-17%), but this was followed by a more rapid and complete recovery, 3) the magnitude of the exercise-induced neuromuscular changes were similar to before training, and 4) higher accumulations of blood lactate and ammonia concentrations after training were observed.

Implication. After a short-term strength training period, the main mechanisms responsible for the increased capacity to work with the same relative intensity are mainly of a peripheral nature, since similar neural adjustments but higher accumulated fatigue and metabolic demand (i.e., blood lactate and ammonia accumulation) were observed after multiple sets of dynamic fatiguing high-power contractions with the same relative load as in pre-training. This result may indicate that rate of fatigue development (i.e., power and maximum voluntary contraction) was faster and more profound after training despite using the same relative intensity. The fact that the same relative loading leads to increased rate of fatigue development after training has important practical implications. This may suggest that despite the enhanced ability to produce maximal strength and muscle power after a strength training program, it is important to note that when prescribing training programs a similar relative load as in pre-training could lead to a greater rate of fatigue development and, therefore, may induce different training effects (i.e., the dynamic training response will be reduced). Basically, this means that heavy resistance training before a specific sport training is inadvisable because the specific sport training will be compromised by the earlier onset of fatigue.

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