Respiratory muscle training in non-athletes and athletes with spinal cord injury: A systematic review of the effects on pulmonary function, respiratory muscle strength and endurance, and cardiorespiratory fitness based on the FITT principle of exercise prescription

BACKGROUND: Respiratory muscle training (RMT) has been recommended to mitigate impacts of spinal cord injuries (SCI), but the optimal dosage in terms of the frequency, intensity, time, and type (FITT principle) to promote health in SCI individuals remains unclear. OBJECTIVE: To discuss research related to the effects of RMT on pulmonary function, respiratory muscle strength and cardiorespiratory fitness in athletes and non-athletes with SCI, presenting the FITT principle. METHODS: We performed a systematic review. PubMed, Lilacs, Scopus, Web of Science, PEDro, SciELO and Cochrane databases were searched between 1989 and August 2018. Participants were athletes and non-athletes with SCI. RESULTS: 4,354 studies were found, of which only 17 met the eligibility criteria. Results indicated that RMT is associated with beneficial changes in pulmonary function and respiratory muscle strength and endurance among athletes and non-athletes, whereas no effect was reported for maximal oxygen uptake. It was not possible to establish an optimal RMT dose from the FITT principle, but combined inspiratory/expiratory muscle training seems to promote greater respiratory changes than isolated IMT or EMT. CONCLUSION: The use of RMT elicits benefits in ventilatory variables of athletes and non-athletes with SCI. However, it remains unclear which RMT type and protocol should be used to maximize benefits.