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

• Respiratory muscle function was assessed during a six-week period of respiratory muscle endurance training.
• Weekly assessed twitch mouth pressure revealed no significant increase.
• Diaphragmatic strength does not increase during six weeks of respiratory muscle endurance 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 ± 18l/min vs. 207 ± 30l/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.