Quantitative assessment of inspiratory loading on postprandial glycemia and metabolic response in healthy adults

Postprandial blood glucose (BG) regulation is a central determinant of metabolic health and cardiometabolic risk. While conventional exercise effectively lowers postprandial BG, alternative approaches that impose minimal musculoskeletal load remain underexplored. Inspiratory loading (IL) —repeated inspirations against graded resistance —selectively activates oxidative respiratory muscles. However, its real-time metabolic and mechanical demands and their influence on systemic glucose regulation have not been quantified. In this study, we quantitatively characterized the concurrent metabolic and mechanical responses to graded IL and examined their acute effects on postprandial BG in healthy adults. Six participants completed three randomized IL sessions—SHAM (no resistance), MOD (~ 40% maximal inspiratory pressure, MIP), and HIGH (~ 60% MIP)—separated by ≥ 72-h washouts. After fasting measurements, participants ingested 45 g of D-glucose followed by a 30-min IL protocol (6 × 4-min bouts with 1-min rest). Oxygen consumption (VO2), heart rate (HR), inspiratory pressure (IP), and estimated work of breathing (eWOB) were continuously recorded, and BG was measured before and after IL. Glucose ingestion elevated BG across all conditions. IL elicited load-dependent increases in VO2, HR, IP, and eWOB, with MOD and HIGH both significantly elevated relative to SHAM. Post-IL, BG decreased in HIGH and MOD but remained elevated in SHAM (p < 0.05). The change in BG correlated inversely with both VO2 and inspiratory effort indices (IP, eWOB; r = − 0.54 to − 0.59). These findings provide quantitative evidence that respiratory muscle activation alone can elevate whole-body metabolic demand and acutely attenuate postprandial BG elevation. Inspiratory loading, therefore, represents a unique, accessible, and time-efficient stimulus capable of engaging both metabolic and mechanical pathways relevant to glycemic regulation across diverse populations.