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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Increased fatigue resistance of respiratory muscles during exercise after respiratory muscle endurance training

Exercise Physiology, Institute for Human Movement Sciences, ETH Zurich, and Institute of Physiology and Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland

Submitted 12 June 2006 ; accepted in final form 19 October 2006

Respiratory muscle fatigue develops during exhaustive exercise and can limit exercise performance. Respiratory muscle training, in turn, can increase exercise performance. We investigated whether respiratory muscle endurance training (RMT) reduces exercise-induced inspiratory and expiratory muscle fatigue. Twenty-one healthy, male volunteers performed twenty 30-min sessions of either normocapnic hyperpnoea (n = 13) or sham training (CON, n = 8) over 4–5 wk. Before and after training, subjects performed a constant-load cycling test at 85% maximal power output to exhaustion (PRE_EXH, POST_EXH). A further posttraining test was stopped at the pretraining duration (POST_ISO) i.e., isotime. Before and after cycling, transdiaphragmatic pressure was measured during cervical magnetic stimulation to assess diaphragm contractility, and gastric pressure was measured during thoracic magnetic stimulation to assess abdominal muscle contractility. Overall, RMT did not reduce respiratory muscle fatigue. However, in subjects who developed >10% of diaphragm or abdominal muscle fatigue in PRE_EXH, fatigue was significantly reduced after RMT in POST_ISO (inspiratory: –17 ± 6% vs. –9 ± 10%, P = 0.038, n = 9; abdominal: –19 ± 10% vs. –11 ± 11%, P = 0.038, n = 9), while sham training had no significant effect. Similarly, cycling endurance in POST_EXH did not improve after RMT (P = 0.071), while a significant improvement was seen in the subgroup with >10% of diaphragm fatigue after PRE_EXH (P = 0.017), but not in the sham training group (P = 0.674). However, changes in cycling endurance did not correlate with changes in respiratory muscle fatigue. In conclusion, RMT decreased the development of respiratory muscle fatigue during intensive exercise, but this change did not seem to improve cycling endurance.

inspiratory muscles; expiratory muscles; endurance; magnetic nerve stimulation

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