Background/Objectives: The COVID-19 pandemic highlighted that body positions substantially
affected the mortality rate. We hypothesized that body position modulates the contribution
of abdominal (AB) and thoracic breathing (TB) to the breathing cycle (BC), as well
as respiratory rate (RR). In addition, we hypothesized that physical activity level
can increase the contribution of abdominal breathing. Methods: Thus, we used plethysmography
respiratory belts to measure changes in abdominal (AB) and thoracic (TB) circumferences,
their ratio (AB/TB), and respiratory rate (RR) under resting conditions. Measurements
were taken in four body positions—standing (St), sitting (Si), supine (Su), and prone
(Pr)—for two groups of young adults (aged 21 ± 2 years) with different physical activity
levels (low and high PA). 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%
(p < 0.001)). AB was significantly the highest in Su and lowest in Si and St (p <
0.001). There was a significant difference in respiratory rate (RR) between the four
body positions (p = 0.005). RR in the four body positions was the following: Si: 15.1,
St: 15.0, Su: 13.7, and Pr: 14.4. RR was the lowest in Su (13.7), where AB was the
highest (56.8%), and RR was the highest in Si (15.1) and St (15.0), where TB was higher
compared to Su (p < 0.001). PA significantly affected the various body positions’
AB/TB ratio and RR. The high PA group showed a significant difference in the AB/TB
ratio between the body positions (p < 0.001). The low PA group showed a significant
difference in RR between the body positions (p = 0.025). Conclusions: In young, healthy
adults, we found that body position significantly influenced 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 potentials for breathing pattern monitoring
and position-based interventions to improve healthcare outcomes and enhance sports
performance and recovery.
