Repeatability of Thoracoabdominal Wall Compartmental Contributions to Tidal Volume during Low‐, Moderate‐ and Heavy‐Intensity Exercise

Abstract

The patterns of breathing and the thoracoabdominal wall compartmental contributions to tidal volume at different exercise intensities are typically assessed during a single laboratory visit, where individuals complete progressively higher intensity stages of exercise. The relative contributions of the thoracic and abdominal compartments have been reported to be invariant across exercise intensities; however, inter-individual differences have been observed. Therefore, the purpose of this study was to assess the repeatability of the compartmental contributions to tidal volume during low-, moderate-, and heavy-intensity exercise. It was hypothesized that the inter-individual differences in the compartmental contributions would be repeatable day-to-day for each intensity. Seven healthy adults (2 female, age: 28±7 yr, peak oxygen uptake: 45±5 ml·min-1·kg-1) completed two step exercise tests on separate days, consisting of low-, moderate-, and heavy-intensity stages for each individual based on their ramp exercise responses. Tidal volume and breathing rate were assessed using a bi-directional turbine, and thoracic and abdominal contributions to tidal volume were measured by respiratory inductance plethysmography. Day-to-day repeatability was evaluated using the intra-class correlation coefficient (ICC). With increasing exercise intensity, the tidal volume (p<0.001) and breathing rate (p<0.001) increased, but no differences in tidal volume (p=0.97; low: 1.14±0.21 L vs. 1.22±0.48 L, moderate: 2.02±0.49 L vs. 1.92±0.54 L, heavy: 2.51±0.60 L vs. 2.54±0.59 L) or breathing rate (p=0.94; low: 18±4 breaths·min-1 vs. 17±6 breaths·min-1, moderate: 22±8 breaths·min-1 vs. 23±7 breaths·min-1, heavy: 37±9 breaths·min-1 vs. 37±10 breaths·min-1) were observed between testing days. The relative contribution of the thoracic (low: 64±12% vs. 63±15%, moderate: 66±12% vs. 64±14%, heavy: 67±11% vs. 67±12%) and abdominal (low: 36±12% vs. 37±15%, moderate: 34±12% vs. 36±14%, heavy: 33±11% vs. 33±12%) compartments did not differ significantly between test days (p=0.59), or exercise intensities (p=0.38). However, there were inter-individual differences in how the compartmental contribution to tidal volume changed with exercise intensity, as the relative contribution of the thoracic compared to abdominal compartment increased with higher intensity exercise for 3 subjects, decreased for 1 subject, and remained relatively constant for 3 subjects. These inter-individual differences to increasing exercise intensity do not appear random, as the test-retest repeatability of the compartmental contribution to tidal volume was good to excellent for low (ICC=0.87, p=0.003), moderate (ICC=0.89, p=0.002) and heavy (ICC=0.93, p=0.001) exercise. Future work should seek to identify factors contributing to the observed inter-individual differences in compartmental contribution to tidal volume with increasing exercise intensity and whether these impart functional consequences.