Respiratory muscle function during a six-week period of normocapnic hyperpnoea training.

Respiratory muscle endurance training (normocapnic hyperpnoea, RMET) improves maximal volitional ventilation (MVV) and respiratory muscle endurance while volitionally-assessed respiratory muscle strength remains unchanged (prior-to-post comparison). What remains unclear is how respiratory muscle function changes/adapts during a defined period of RMET in highly-trained subjects. This study assessed respiratory muscle function during a six-week period of RMET in 13 highly-trained, healthy subjects. Weekly-assessed twitch mouth pressure (prior/post 2.20 ± 0.41 kPa vs. 2.43 ± 0.61 kPa; p=0.14); twitch transdiaphragmatic pressure (prior/post 3.04 ± 0.58 kPa vs. 3.13 ± 0.48 kPa; p=0.58) and maximal inspiratory pressure (prior/post 12.6 ± 3.6 kPa vs. 13.9 ± 3.8 kPa; p=0.06) did not increase. MVV (prior/post 175 ± 18 l/min vs. 207 ± 30 l/min; p=0.001), sniff nasal pressure (prior/post 11.8 ± 2.8 kPa vs. 14.0 ± 2.9 kPa; p=0.003) and maximal expiratory pressure (prior/post 16.9 ± 5.8 kPa vs. 20.9 ± 4.9 kPa; p=0.006) each increased. In conclusion, non-volitionally assessed diaphragmatic strength does not increase during six weeks of RMET in highly-trained subjects, while expiratory muscle strength and MVV rose. Future studies should clarify if these findings apply when assessed during respiratory muscle strength rather than endurance training.