Effects of resistive respiratory muscle training followed by voluntary isocapnic hyperpnea training on the respiratory muscle and exercise performance in healthy human subjects
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Several studies have suggested that specific respiratory muscle training can improve both strength and endurance of respiratory muscles and consequently exercise performance. However, the effects of these improvements on exercise performance remain controversial. A combination of a four-week, 12-session resistive respiratory muscle training (RRMT) in nine experienced runners (five men, four women) followed by a four-week, 12-session voluntary isocapnic hyperpnea training (VIHT) in seven experienced runners (two subjects were withdrawn, five men, two women) was conducted to determine if they improved respiratory muscle performance and whole-body exercise performance. The following measurements were performed before and after (two weeks) each training period: slow vital capacity (SVC), forced vital capacity (FVC), maximum voluntary ventilation in 15 seconds (MVV 15 ), forced expired volume in one second (FEV 1 ), maximal inspiratory and expiratory mouth pressures (P I max and P E max ), maximal oxygen uptake (V O2 max ), running endurance capacity to voluntary exhaustion at 80% V O2 max , blood lactate concentration (BLC), minute ventilation (V E ), respiratory muscle endurance (RET), and CO 2 sensitivity. There were no statistically significant differences in post-RRMT and post-VIHT pulmonary functions, CO 2 sensitivity and maximal exercise performance on average. The inspiratory muscle strength significantly improved by 23.8 ± 30% and 18.7 ± 21.4% at rest and immediately after the running test, respectively, following RRMT but not after VIHT or completion of RMT (RRMT + VIHT). After RRMT, VIHT and RMT, the respiratory muscle endurance increased by 6.8 ± 75.7%, 241.8 ± 185.2% and 222 ± 207.8%, and the duration of constant-load endurance running test was increased by 15.7 ± 26.7%, 6.77 ± 18.4%, 29.6 ± 45.3%, respectively; however, these improvements failed to achieve statistical significance. RRMT showed statistically significant improvements in respiratory muscle strength, while VIHT showed an improvement in respiratory endurance; however, these changes failed to translate into significant improvements in exercise performance. The most likely explanation of the failure of this study to confirm the results of previous studies was that the subjects did not perform the training appropriately. The subjects who performed training appropriately improved running endurance, P I max , P E max , and RET. Key words: Resistive respiratory muscle training, voluntary isocapnic hyperpnea training, respiratory, exercise, endurance, maximal oxygen consumption.