Effects of Sprint Interval and Endurance Respiratory Muscle Training on Postcycling Inspiratory and Quadriceps Fatigue

PurposeWe investigated whether a 4-wk period of respiratory muscle endurance training (RMET) or respiratory muscle sprint interval training (RMSIT) would lead to an attenuation of inspiratory muscle and quadriceps fatigue after a bout of high-intensity cycling compared with a placebo intervention (PLAT), as predicted by the respiratory metaboreflex model.MethodsThirty-three active, young healthy adults performed RMET, RMSIT, or PLAT. Changes in inspiratory muscle and quadriceps twitches in response to a cycling test at 90% of peak work capacity were assessed before and after training. EMG activity and deoxyhemoglobin (HHb, via near-infrared spectroscopy) of the quadriceps and inspiratory muscles were also monitored during the cycling test, along with cardiorespiratory and perceptual variables.ResultsAt pretraining, cycling reduced the twitch force of the inspiratory muscles (86% & PLUSMN; 11% baseline) and quadriceps (66% & PLUSMN; 16% baseline). Training did not attenuate the drop in twitch force of the inspiratory muscles (PLAT, -3.5 & PLUSMN; 4.9 percent-points [p.p.]; RMET, 2.7 & PLUSMN; 11.3 p.p.; RMSIT, 4.1 & PLUSMN; 8.5 p.p.; group-training interaction, P = 0.394) or quadriceps (PLAT, 3.8 & PLUSMN; 18.6 p.p.; RMET, -2.6 & PLUSMN; 14.0 p.p.; RMSIT, 5.2 & PLUSMN; 9.8 p.p.; group-training interaction P = 0.432). EMG activity and HHb levels during cycling did not change after training for either group. Only RMSIT showed a within-group decrease in the perception of respiratory exertion with training.ConclusionsFour weeks of RMET or RMSIT did not attenuate the development of exercise-induced inspiratory or quadriceps fatigue. The ergogenic effects of respiratory muscle training during whole-body exercise might be related to an attenuation of perceptual responses.