Body Positions and Physical Activity Levels Modulate Breathing Mechanics in Young Individuals

Objectives: Body positioning during in-hospital care significantly impacted mortality rates during the COVID-19 pandemic. However, less is known about how different body positions and regular physical activity levels affect breathing mechanics. Hypothesis: We hypothesized that 1) body position changes the contributions of abdominal (AB) and thoracic breathing (TB) to the breathing cycle (BC) and the respiratory rate (RR), and that 2) higher regular physical activity increases the contribution of abdominal breathing to BC. Methods: Plethysmography respiratory belts were used to measure changes in abdominal (AB) and thoracic (TB) circumferences and respiratory rate (RR) under resting conditions. Measurements were taken in four body positions: standing (St), sitting (Si), supine (Su), and prone (Pr), in two groups of young adults (aged 21 ± 2 years) with different physical activity levels (low PA and high PA). Statistical analyses were performed using IBM SPSS, with a significance level of p < 0.05. Results: The AB/TB ratios significantly differed between the body positions Si: 45.5/54.5%, St: 40.5/59.5%, Su: 56.8/43.2%, Pr: 52.2/47.8%. AB was significantly the highest in Su and lowest in Si and St. The respiratory rate, RR (1/min), in the four body positions were Si: 15.1, St: 15.0, Su: 13.7, Pr: 14.4). RR was lowest in Su (13.7), where AB was highest (56.8%), and RR was the highest in Si (15.1) and St (15.0), where TB was higher compared to Su. The AB/TB ratio in the Su, Si, and St positions was significantly higher in the high PA group compared to the low PA group. In the high PA group, the AB/TB ratio differed between the Su, St, and Si positions. In the low PA group, the respiratory rate (RR) was significantly higher in the Si compared to the Su position. Conclusions: In young, healthy adults, body positions significantly modulated the abdominal/thoracic breathing ratio during the breathing cycle. The supine position showed the highest contribution of abdominal breathing, which correlated with the lowest respiratory rate. Additionally, a higher level of physical activity increased the contribution of abdominal breathing in the Si, Su, and St positions, suggesting a more energy-efficient breathing pattern. These findings suggest the potential for breathing pattern monitoring and body position-based interventions to improve healthcare outcomes and enhance sports performance and recovery. Ministry for I and T, Hungary, NRDI Fund, TKP2020-NKA-17, TKP2021-EGA-37, OTKA K-132596 (AK), TKP2021-EGA-25 (TJ); Hungarian Academy of Sci, Post-COVID 2021-34. This abstract was presented at the American Physiology Summit 2025 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.