The recent study by Vašíčová et al. (2017) described novel findings that respiratory muscle training (RMT) improved respiratory muscle strength and swimming performance in an apnea-max swim test in young fin-swimmers. These positive findings are largely compatible with established literature demonstrating increases in respiratory muscle strength following RMT (HajGhanbari et al., 2013; Illi et al., 2012; Shei et al., 2016b) and improvements in swimming performance (Kilding et al., 2010; Wylegala et al., 2007). However, several important points should be considered when interpreting these findings.

First, given that water-based exercise, such as conventional swimming and fin-swimming, requires athletes to exercise while immersed in water, the additional hydrostatic pressure that surrounds the thoracic cavity presents an additional load which must be overcome by the inspiratory muscles in order to generate inspiratory airflow to the lungs. Consequently, swimmers are known to have above-normal spirometry and higher pulmonary diffusion capacity (Mickleborough et al., 2008). Further, regular aquatic exercise may mimic resistive inspiratory muscle training. Elite adult swimmers who engaged in a 12-week competitive swim training program exhibited similar improvements in pulmonary and respiratory muscle function compared to those who completed flow-resistive inspiratory muscle training in addition to the same swim training program (Mickleborough et al., 2008). Comparatively, sub-elite adult swimmers, who had a markedly lower training volume and intensity compared to the elite swimmers, did receive additional benefits from combining flow-resistive inspiratory muscle training and swim training (Shei et al., 2016a), indicating that there may be a dose-response relationship to swim training and its effects on pulmonary and respiratory muscle function. The present study by Vašíčová et al. (2017) did not report training volume and intensity of the youth fin-swimming population that was studied, therefore it is difficult to determine whether the fin-swimming training program they engaged in may have influenced their findings. Further, the study did not include a group that completed placebo RMT, despite the availability of several sham-IMT protocols that have been shown to have no effect on pulmonary and respiratory muscle function (Shei et al., 2016b). Including a placebo RM group would have allowed the authors to parse out differences between fin-swim training alone and fin-swim training with placebo-RMT.

Second, it appears from Tables 1 and 2 in the study by Vašíčová et al. (2017), that the control group (CG) may have had significantly higher spirometry values at baseline, although no statistical measures of variation (SD or SE) or inferential statistics were reported. Similarly, baseline PI_max appears to be greater in the CG group at baseline as well. These apparent differences in pulmonary and respiratory muscle function between groups at baseline raises concern about whether group assignment was properly controlled, and may have influenced the results of the study.

Finally, although the authors have speculated at a mechanistic link between increased respiratory muscle strength (increases in PI_max and PE_max) and improved apnea-max swim performance, they failed to record any measures of respiratory muscle endurance such as sustained maximal inspiratory pressure and maximal voluntary ventilation. It is likely that respiratory muscle training influences both respiratory muscle strength and endurance, although presently it is equivocal which is more pertinent to improving performance. However, given that the criterion measure of performance in this study was an apnea-max test, performed for the duration of one single inspiration, it is difficult to determine how increased respiratory muscle strength could affect performance during this task since the subjects were holding their breath (presumably at or near total lung capacity). On one hand, it is possible that improvements in inspiratory muscle strength would allow subjects to complete this breath-hold during the apnea-max swim test at a lower intensity relative to maximal inspiratory pressure-generating capacity (since PI_max was higher post-training), however how this influences performance is unclear. Inspiratory muscle training has been demonstrated to reduce the oxygen cost of voluntary hyperpnea in trained cyclists (Turner et al., 2012), however it is presently unknown whether this improvement in respiratory muscle economy would translate to reduced oxygen cost of a single breath hold at or near total lung capacity. If this were the case, this may provide a mechanistic link to explain, in part, the findings of improved apnea-max swim performance observed by Vašíčová et al. (2017).

In summary, the novel findings by Vašíčová et al. (2017) provide an interesting glimpse into how RMT can influence performance in aquatic sports, even during a criterion task that does not require voluntary hyperpnea, but instead, requires a single-breath hold for the duration of the exercise task. Their findings present several interesting areas for future inquiry that are presently unanswered. Future studies should aim to evaluate the mechanistic link between RMT, its effects on pulmonary and respiratory muscle function, and performance.

REFERENCES

HajGhanbari, B., Yamabayashi, C., Buna, T.R., Coelho, J.D., Freedman, K.D., Morton, T.A., Palmer, S.A., Toy, M.A., Walsh, C., Sheel, A.W. and Reid W.D. (2013) Effects of respiratory muscle training on performance in athletes: A systematic review with metaanalyses. Journal of Strength and Conditioning Research 27, 1643-1663.

Illi S.K., Held U., Frank I. and Spengler, C.M. (2012) Effect of respiratory muscle training on exercise performance in healthy individuals: a systematic review and meta-analysis. Sports Medicine 42, 707-724.

Kilding, A.E., Brown, S. and McConnell, A.K. (2010) Inspiratory muscle training improves 100 and 200 m swimming performance. European Journal of Applied Physiology 108, 505-511.

Mickleborough, T.D., Stager, J.M., Chatham, K., Lindley, M.R. and Ionescu, A.A. (2008) Pulmonary adaptations to swim and inspiratory muscle training. European Journal of Applied Physiology 103, 635-646.

Shei, R-J., Lindley, M.R., Chatham, K. and Mickleborough, T.D. (2016a) Effect of flow-resistive inspiratory loading on pulmonary and respiratory muscle function in sub-elite swimmers. Journal of Sports Medicine and Physical Fitness 56, 392-398.

Shei, R-J., Paris, H.LR., Wilhite, D.P., Chapman, R.F. and Mickleborough, T.D. (2016b) The role of inspiratory muscle training in the management of asthma and exercise-induced bronchoconstriction. The Physician and Sportsmedicine 44, 327-334.

Turner, L.A., Tecklenburg-Lund, S.L., Chapman, R.F., Stager, J.M., Wilhite, D.P. and Mickleborough, T.D. (2012) Inspiratory muscle training lowers the oxygen cost of voluntary hyperpnea. Journal of Applied Physiology 112, 127-134.

Vašíčková, J., Neumannová, K. and Svozil, Z. (2017) The effect of respiratory muscle training on fin-swimmers' performance. Journal of Sports Science and Medicine 16, 521-526.

Wylegala, J.A., Pendergast, D.R., Gosselin, L.E., Warkander, D.E. and Lundgren, C.E.G. (2007) Respiratory muscle training improves swimming endurance in divers. European Journal of Applied Physiology, 99, 393-404.