To examine the effects of locomotor frequency and respiratory drive on the incidence of locomotor-respiratory coupling (i.e. entrainment), we examined the relationship between locomotor and ventilatory patterns in trained Canada geese that were: (1) running at three speeds (0–40, 0–52 and 0–72 ms−1) on a treadmill, (2) free-running at three velocity intervals (0–40–0–72, 1–0–1–5 and 1–5–2–Oms−11) overground, and (3) breathing hypoxic (12 % O2/ l % CO2) and hypercapnic (5 % CO2/30% O2) gas mixtures while running at one speed (0–52ms−1) on the treadmill.
The portion of the time that the locomotor and respiratory systems were coupled was significantly greater during overground locomotion (41.1±3.2%) than at comparable speeds on the treadmill (29.0±2.6%). In addition, a significant increase in coupling with velocity was only observed during overground locomotion (41%1 ±3.2% at 0.40–0-72ms−1 vs 57.7 ±6.3% at 1.5–2.0ms−1).
This increase in entrainment appeared to be the direct result of an increase in locomotor frequency per se and not due to the increase in metabolic rate associated with greater locomotion velocity.
The effects of hypercapnia on the degree of entrainment were unclear owing to inter-animal variability; however, hypoxia caused a substantial decrease in entrainment from air-breathing values (34.8 ± 3.9 %) to levels not different from those possible due to chance alone (20%).
Thus, it appears that locomotor pattern does entrain ventilatory rhythm and that the degree of entrainment is partially dependent on limb movement frequency. However, the increased respiratory drive associated with hypoxia appears to override the influence of locomotor rhythm on respiratory pattern, with a subsequent decrease in entrainment.