Resistance-based Inspiratory Muscle Training Improves Cycling Power in Females Despite Minimal Diaphragm Hypertrophy

Severe-intensity exercise leads to a non-linear increase in total ventilation and a rise in the work of breathing (Wb). Increased Wb accelerates diaphragmatic fatigue and increases sympathetic activation, causing vasoconstriction in the locomotor muscles to redistribute blood flow toward the diaphragm. Inspiratory muscle training (IMT) may attenuate this response by strengthening the respiratory muscles and reducing their reliance on substrate-level metabolism and activation of the metaboreflex. We tested the hypothesis that resistance-based IMT would increase diaphragm thickness, inspiratory muscle strength, and maximal cycling power during a VO 2 peak test. Twenty-four young adults (female: n = 12, male: n = 12) participated in the study. Measurements of diaphragm thickness (via ultrasound), inspiratory muscle strength (strength index, S-Index), and cardiopulmonary exercise fitness (cycling VO 2 peak) were measured pre and post 5-6 weeks of resistance IMT (5-6 days/week). Following the IMT intervention, S-Index significantly increased compared to baseline values (Pre-IMT: 137.26 ±46 cmH2O; Post-IMT: 181.2 ± 40 cmH2O, p < 0.001). Although diaphragm thickness showed a 6.71% numerical increase, the change was not statistically significant (Pre-IMT: 2.46 ± 0.8 mm; Post-IMT: 2.63 ± 0.7 mm, p = 0.0503). Inspiratory muscle training significantly improved VO 2 peak power output in females (Pre-IMT: 219.59 ± 68 W; Post-IMT: 236.37 ± 64 W, p = 0.006), but there was no significant change in VO 2 peak (Pre-IMT: 43.37 ± 9 ml/kg/min; Post-IMT: 44.27 ± 9 ml/kg/min, p = 0.19). These findings suggest that five to six weeks of resistance-based IMT significantly improves inspiratory muscle strength and cycling power during VO 2 peak testing in females, potentially enhancing tolerance to severe-intensity exercise. While the mechanistic basis of these effects remains to be explored, these results may be relevant for clinical populations with elevated Wb and reduced exercise capacity, as well as for athletes and those exposed to high-altitude environments, where the Wb is elevated. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.