Research has found that breathing is entrained to the locomotive rhythm, with its occurrence increasing with fitness level and experience with the activity. Highly trained runners are a unique population in which to study this "lungs-legs" relationship given their high ventilatory workloads.
PURPOSE: To examine entrainment of breathing frequency to stride rate in distance runners while running at 70, 90, 100, and 110% of ventilatory threshold (VT), to compare the degree of entrainment between % VT intensities, and to examine the relationship between entrainment and running economy (RE) at each intensity. Differences in entrainment between subjects who exhibited exercise-induced hypoxemia (EIH) and expiratory flow limitation (FL) were also explored.
METHODS: 15 male highly trained distance runners performed a VO2max test and a locomotor-respiratory coupling test, during which RE was determined at each intensity. EIH and FL were determined by pulse oximetry and flow-volume measurements, respectively.
RESULTS: Only 5 subjects exhibited EIH and 2 exhibited FL, precluding group comparisons regarding entrainment. All subjects entrained breathing to stride rate, precluding group comparisons regarding RE. Step-to-breath ratios decreased with increasing intensity up to 100% VT (2.75 ± 0.58, 2.32 ± 0.52, and 2.14 ± 0.56; p<0.05) but did not decrease further at 110% VT (2.16 ± 0.48). Subjects most often used 5:3 and 2:1 ratios. Percent entrainment increased with intensity during inspiration (13.1 ± 7.8, 23.1 ± 14.5, 28.4 ± 16.5, and 30.8 ± 14.9% for 70, 90, 100, and 110% VT, respectively; p<0.01), but not during expiration (30.8 ± 12.6, 27.9 ± 10.0, 20.8 ± 7.3, and 25.7 ± 11.2%, respectively). At all intensities, percent entrainment was significantly greater than a chance occurrence. Correlations between degree of entrainment and RE were not significant at any intensity.
CONCLUSION: Entrainment of breathing to locomotion is a physiological phenomenon in highly trained distance runners, which is not influenced by intensity, but can differ between inspiration and expiration. Furthermore, RE is not associated with entrainment.