VO2 kinetics in the horse during moderate and heavy exercise.

This study examines how the rate of oxygen uptake (VO2) varies in horses during different levels of exercise intensity. The researchers found that despite some similarities, there are notable differences between horses and humans in terms of their VO2 uptake rate and the influence of exercise intensity on it.

Research Methodology

• The study participants consisted of adult male horses who underwent a series of tests on a treadmill at increasing intensity levels. These tests aimed to determine the horses’ lactate threshold (Tlac) and peak VO2 (VO2 peak).
• The kinetic features of VO2 responses to work forcings were studied using exercise transitions from a slow speed (3 m/s) to a moderately intense speed (7 m/s, below Tlac), and to a high intensity speed (12.3 ± 0.7 m/s, between Tlac and VO2 peak).
• Measurements were made during exercise intervals lasting 6 minutes, and an open-flow system was used to measure VO2 and CO2 output.
• The researchers also monitored the pulmonary artery temperature and analysed the mixed venous blood for plasma lactate concentrations.

Key Findings

• VO2 kinetics at speeds below the Tlac were found to fit a two-phase exponential model, with a delay time and a phase 2 time constant that were similar to those found in humans performing leg cycling exercise.
• However, the time constant was much faster than in humans, indicating a more rapid response
• When speeds exceeded the Tlac, the delay time remained almost unchanged, however, the phase 2 time constant was found to be slower.
• A slow secondary increase in VO2 was observed in four out of five horses approximately 136 seconds after the exercise transition. This slow component accounted for approximately 12% of the net increase in exercise VO2.

Conclusion

• The researchers concluded that the VO2 kinetics’ qualitative features in horses are comparable to those in humans, both below and above the lactate threshold.
• However, at exercise speeds below Tlac, the fast component of the response is more rapid in horses than in humans. This difference may reflect varying energetics of oxygen utilization within the equine muscle.