Effects of a 4-week inspiratory muscle training program on the performance in distance runners : a randomized controlled trial

Background: Distance running is one of the most popular sports globally. Running economy in terms of oxygen consumption (VO2) is strongly associated with running performance. In distance running, respiratory muscles are important in maintaining sufficient alveolar ventilation and oxygen supply. Fatigue of respiratory muscles can increase work of breathing and oxygen demand by the respiratory muscles which further limit the total blood flow to peripheral muscles thus affect exercise performance. Inspiratory muscle training (IMT) has been reported to improve the strength and endurance of respiratory muscle by increasing the percentage of type I fibers and the size of type II fibers. This may reduce the energy requirement for ventilation and hence lessening the lactate accumulation. All these may eventually lead to performance enhancement. However, the association of these proposed mechanisms remains speculative. Purpose: The main aims of this double blinded randomized controlled trial were to (1) investigate if a 4-week progressive IMT program could improve the 10-km running performance in distance runners; and (2) examine whether the changes are associated with any of the proposed mechanisms, i.e. respiratory muscle strength, oxygen consumption and lactate accumulation. Methods: Twenty-one healthy recreational 10-km runners were randomly allocated into IMT or control (CON) group. True IMT trainers and placebo trainers were given to IMT group (n = 11) and CON group (n = 10) respectively for a 4-week program. Assessments were conducted before and after the program. In each assessment session, inspiratory muscle strength, 10-km completion time, peak oxygen consumption (peak VO2) during 10-km running bout, and lactate accumulation after the running bout were measured. Results: Significant increase in the maximal inspiratory pressure (17.2%, p = 0.002) was observed in the IMT group but not in CON group. Though statistically insignificant, an improvement trend in 10-km completion time by 6.05% (p = 0.083) was noted in the IMT group but not in the CON group. However, no significant within nor between-group differences were observed in other outcome measures. Conclusion(s): This study showed that inspiratory muscle training is effective in strengthening inspiratory muscle in distance runners. However, no significant changes in exercise performance were observed. Further studies adopting a protocol with longer training duration are warranted. Implications: IMT is effective in strengthening inspiratory muscle in distance runners and there are signs that the improved inspiratory muscle strength may enhance running performance.