VO2 recovery kinetics in the horse following moderate, heavy, and severe exercise

At the onset of exercise, horses exhibit O-2 uptake (V) over dot O-2) kinet ics that are qualitatively similar to those of humans. In humans, there is a marked dissymmetry between on- and off-kinetics for (V) over dot O-2,. Th is investigation sought to formally characterize the off-transient (recover y) (V) over dot O-2, kinetics in the horse within the moderate (M), heavy ( H), and severe (S) exercise domains. Six horses were run on a high-speed tr eadmill at M, H, and S exercise intensities (i.e., that speed which yielded similar to 50, 85, 100% peak (V) over dot O-2, respectively, on the maxima l incremental test). The time courses for the recovery were modeled by usin g a three-phase model with a single-exponential (fast component) or double- exponential (fast and slow component) phase 2. The single-exponential phase 2 model provided an excellent fit to the off-transient data, with the exce ption of one horse in the H domain which was best modeled by a double expon ential. The time delay elicited no domain dependency (M, 18.0 +/- 1.0; H, 1 7.6 +/- 1.1; S, 17.8 +/- 2.0 s; P > 0.05), as was the case for the fast-com ponent time constants (M, 16.3 +/- 2.0 s; H, 13.5 +/- 1.0 s; S, 14.6 +/- 0. 3 s; P > 0.05). In the H and S (but not M) domains, the (V) over dot O-2 fo llowing resolution of the fast component was elevated above the preexercise baseline (H, 3.0 +/- 1.0 l/min; S, 5.7 +/- 1.1 l/min). This additional-pos texercise (V) over dot O-2 was correlated to the end-exercise increase in l actate (r = 0.94, P < 0.001) but not the end-exercise pulmonary arterial bl ood temperature (r = 0.45, P > 0.05). These data indicate that the time del ay and subsequent kinetic response of the primary (fast-component) phase of exercise (V) over dot O-2 recovery in the horse is independent of the prec eding exercise-intensity domain. However, in the H and S domains, the fast component resolves to an elevated baseline.