Oxygen Cost of Breathing During Voluntary Eucapnic Hyperpnea Among Adults with Obesity After Inspiratory Muscle Strength Training

Exercise intolerance in stage 3 obesity may stem from weak inspiratory muscles, which can increase dyspnea and the oxygen cost of breathing. Inspiratory muscle strength training (IMST) increases inspiratory muscle strength and exercise tolerance among older adults with above-normal blood pressure; however, it is unclear whether IMST can reduce dyspnea and the oxygen cost of breathing in younger adults with stage 1 and 2 obesity. PURPOSE: To test the hypothesis that 8 weeks of IMST reduces dyspnea and the oxygen cost of breathing during eucapnic voluntary hyperpnea (EVH) among younger adults with obesity. METHODS: Using a triple-masked, parallel-arm, sham-controlled design, we randomized otherwise healthy adults (20–35 yrs) with obesity (body mass index [BMI] 30–40 kg/m 2 ) to daily training at 75% (IMST) or 15% (SHAM) of their maximal inspiratory pressure (MIP) for 8 weeks. Pre- and post-intervention, we determined the oxygen cost of breathing by calculating the slope of oxygen uptake ([Formula: see text]O 2 ), measured via indirect calorimetry, during a 5-minute resting baseline and the final minute of 5-minute EVH stages performed at 40 and 60 L/min. We used the Modified Borg Dyspnea Scale (0–10) and Rating of Perceived Exertion Borg Scale (6–20) in the last minute of each stage. Respiratory rate was maintained at 20 breaths per minute with a 1:1 duty cycle. We compared mean changes (Δ, post-minus pre-training) using unpaired, two-tailed t-tests and Cohen’s d. We assessed the relation between ΔMIP and Δ oxygen cost of breathing slope with Spearman's rank correlation (ρ). We report data as mean ± SD or median [IQR]. RESULTS: Participant (n=17) characteristics were: 26 ± 4 yrs; 95.4 ± 15.7 kg; BMI 32.8 ± 2.7 kg/m2; MIP 115 ± 30 cmH 2 O, MIP 95 ± 20 % of predicted; training compliance 89 [11] %; 47 % female; 30 % Latine; 76 % White, 18 % Black, and 6 % Other. Pre-training BMI, absolute MIP, percent predicted MIP, resting [Formula: see text]O 2 , and training compliance did not differ between groups (P≥0.11 for all). ∆ MIP (IMST: 32 ± 26 vs. SHAM: 17 ± 26 cmH 2 O, P=0.512 d=0.56) did not differ between groups. The ∆ oxygen cost of breathing slope (IMST: -0.05 ± 2.43 vs. SHAM: 0.05 ± 1.02 ml/min, P=0.92, d=0.05), ∆ rating of perceived breathlessness (IMST: 0.0 ± 1.0 vs. SHAM: 0.0 ± 2.0, P=0.93, d=0.04), and ∆ perceived exertion (IMST: -1 ± 3 vs. SHAM: -1 ± 4, P=0.97, d=0.02) were not different between groups. Interestingly, regardless of group, there was a moderate inverse correlation between absolute ∆ MIP and ∆ oxygen cost of breathing slope (ρ=-0.50, P=0.04). CONCLUSION: These preliminary findings suggest that IMST intensity does not affect the oxygen cost of breathing or dyspnea among younger adults with obesity. However, increasing inspiratory muscle strength was associated with a reduced oxygen cost of breathing among younger adults with obesity. 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.