Emotional excitability influences horses' performance in sports and races. The aim of the study was to analyse whether the balance of the autonomic system which can occur when sympathetic system activity is at various levels might impact the horses' racing performance. The study was carried out on 67 purebred Arabian horses trained for racing. The following indices were analysed: low frequency (LF), high frequency (HF), and the ratio of spectrum power at low frequencies to high frequencies (LF/HF). The autonomic nervous system activity was measured × 3 during the training season, at three-month intervals. Each examination included a 30-min measurement at rest and after a training session. The racing performance indices in these horses were also analysed. Better racing results were found in horses with enhanced LF/HF. The worst racing results were determined in horses with low LF.
Racehorses, heart rate variability, ANSThe autonomic nervous system is characterised by an irregular distribution of centres, relatively slow conduction of nervous impulses, smooth muscles acting as effectors, and cardiac-type striated tissue and glands (Low 1993). There are numerous autonomic nervous system functions; heart rate acceleration or deceleration being one of them. The autonomic system is divided into the sympathetic system (stimulating) and the parasympathetic system (inhibiting) (Verrier and Lown 1978). All the internal organs are innerved simultaneously by both of these systems. The sympathetic and parasympathetic system activities are antagonistic to each other. In stressful situations, the sympathetic system activity dominates the effects of the parasympathetic component (Baselli et al. 1987, Gill 2003). An increase in the sympathetic component, together with the secretion of epinephrine and norepinephrine, accelerates the heart rate, whereas an increased tone of the parasympathetic system (acetylocholine secretion) decreases the heart rate (Dempsey and Cooper 1969).The activity and balance of the autonomic system can be analysed by measuring the variability of the sinus rhythm (heart rate variability, HRV). This variability is a cyclic occurrence of differences in R-R intervals (the time between complexes of QRS waves in electrocardiogram). The R-R depends on the effects of the mechanisms controlling the activity of the sinoatrial node (Kautzner 1995;von Borell et al. 2007). The rhythm variability can be investigated with a number of methods, including a time method and a frequency (spectral) method (Noszczyk-Nowak and Bogucki 2013;. The spectral method allows to precisely determine whether the autonomic system balance results simply from low activity of the sympathetic system or from high activity of the sympathetic component accompanied by high activity of the parasympathetic system. A lack of balance in the autonomic system unambiguously