Effect of repeated exercise and recovery on heart rate variability in elite trotting horses during high intensity interval training.

This research investigates changes in heart rate variability (HRV) in elite trotting horses during high intensity interval training. The study discovered meaningful alterations in HRV markers linked to changes in stride and breathing frequencies during exercise and recovery phases, potentially indicating early signs of fatigue.

Methodology and Participants

• The researchers collected data from seven elite trotting horses during a high-intensity interval training session.
• The interval training composed five successive 800-meter high-velocity trotting runs, each separated by one-minute low-speed recovery bouts.
• They recorded the RR interval time series (the time between successive heartbeats) for each horse.
• Fast Fourier transform (FFT), a method for transforming a function of time into a function of frequency, and Poincaré plot, a graphical representation of the correlation between successive RR intervals, were utilized to analyze the RR series.

Findings

• Despite constant trotting velocities during the high-speed and recovery stages, repeated exercise resulted in a decrease in mean RR interval and the root mean square of successive differences in RR series (RMSSD). This condition indicates significant changes in HRV components during interval training.
• Both high-speed and recovery repetitions prompted an increase in high frequency (HF) peak of HRV (fHF), which correlates with a horse’s breathing and stride frequencies during trotting.
• Meanwhile, recovery resulted in a decrease in the standard deviation of the successive RR series (SDRR) and the long term index of Poincaré plot (SD2). This finding suggests a decline in the recovery pattern, probably associated with the onset of fatigue.

Conclusions

• The observed increase in fHF during the interval training could have been influenced by modifications in the coupling between breathing and stride frequency resulting from the onset of fatigue.
• The decrease in SD2 and SDRR during successive recovery bouts could be pointing towards a deteriorating recovery pattern.
• The alterations seen in HRV, which can be recorded using HR monitors, can provide vital information regarding a horse’s breathing frequency during training without requiring a respiratory device.
• These changes may also serve as useful markers of fatigue onset during training, offering valuable information to trainers to optimize training schedules and prevent overtraining.