TDK conference 2013

The heart rate shows the net interaction between the parasympathetic (PNS) and sympathetic (SNS) tone in the body. The time interval between two heartbeats or better two R-peaks always differs a little. These little changes are reflecting the SNS and PNS contributions to autonomic nervous system (ANS) modulation of the heart rate. Heart rate variability (HRV) is a noninvasive measurement for the evaluation of this changes giving information about the physical and/or psychical stress affecting the horse.

The aim of the study was to monitor HRV changes in different intensity of exercise, and to assess the mental stress caused by racing.

In the present investigation heart rate and heart period (RR-interval) data were collected at rest, during aerobic training and anaerobic exercise from 8 Standardbred trotters. The anaerobic work was performed under real race circumstances. HRV was analyzed with the Kubios HRV software. Frequency and spectral power were determined in three frequency bands: very low (VLF), low (LF) and high (HF) cycles/beat. Indicators of sympathetic (LF/HF) and parasympathetic (HF) activity were calculated.

LF/HF was higher during the warming up period before racing, than at the same workload on a simple training day, but the difference did not reach statistical significance. HF did not differ significantly on different workloads but it was significant higher at rest (p<0.001). During the most intensive workload of the race (last minute of the competition) the HF and LF/HF was significantly higher and lower compared to the training results, respectively (p<0.0001).

LF/HF reflects the sympathetic activity of the body. Significant increase in the LF/HF was expected before racing, however the reason of the absent sympathetic prevalence can be, that the horses used in the experiment were accustomed to racing and were kept on the same racing center during the whole year. Another surprising result was the decrease of LH/HF and increase of HF during the most intensive exercise. It can be the result of the exhaustion stage of the physical and psychical stress affecting the horse, but also can happen because at this level of work, humoral and other non-neural mechanisms may become more important than autonomic modulation in influencing HR and HRV.

The investigation was supported by the NKB 2013/15905 project.