Effects of Age, Exercise Duration, and Test Conditions on Heart Rate Variability in Young Endurance Horses

Abstract

Although cardiac recovery is an important criterion for ranking horses in endurance competitions, heart rate variability (HRV) has hardly ever been studied in the context of this equestrian discipline. In the present study, we sought to determine whether HRV is affected by parameters such as age, exercise duration and test site. Accordingly, HRV might be used to select endurance horses with the fastest cardiac recovery. The main objective of the present study was to determine the effects of age, exercise duration, and test site on HRV variables at rest and during exercise and recovery in young Arabian endurance horses. Over a 3-year period, 77 young Arabian horses aged 4–6 years performed one or more exercise tests (consisting of a warm-up, cantering at 22 km.h−1and a final 500 m gallop at full speed) at four different sites. Beat-to-beat RR intervals were continuously recorded and then analyzed (using a time-frequency approach) to determine the instantaneous HRV components before, during and after the test. At rest, the root-mean-square of successive differences in RR intervals (RMSSD) was higher in the 4-year-olds (54.4 ± 14.5 ms) than in the 5-or 6-year-olds (44.9 ± 15.5 and 49.1 ± 11.7 ms, respectively). During the first 15 min of exercise (period T), the heart rate (HR) and RMSSD decreased with age. In 6-year-olds, RMSSD decreased as the exercise duration increased (T: 3.0 ± 1.4 vs. 2T: 3.6 ± 2.2 vs. 3T: 2.8 ± 1.0). During recovery, RMSSD was negatively correlated with the cardiac recovery time (CRT) and the recovery heart rate (RHR; R = −0.56 and −0.53, respectively; p < 0.05). At rest and during exercise and recovery, RMSSD and several HRV variables differed significantly as a function of the test conditions. HRV in endurance horses appears to be strongly influenced by age and environmental factors (such as ambient temperature, ambient humidity, and track quality). Nevertheless, RMSSD can be used to select endurance horses with the fastest cardiac recovery.

The use of heart rate variability analysis to detect arrhythmias in horses undergoing a standard treadmill exercise test

“…When comparing traditional time domain and nonlinear HRV parameters, we were particularly interested in the short‐term variability parameter RMSSD. During trot and canter, RMSSD was low in horses without arrhythmias and similar to those previously reported during ridden exercise or in trotters . This value increased during recovery as parasympathetic tone increased, although there was a wide inter‐horse variation seen during this recovery phase.…”

“…Many of these studies were performed using a HR monitor rather than an ECG, and arrhythmic beats were either not mentioned or excluded from the analysis using automated or manual filtering. None of these older studies have provided clear information on percent instantaneous beat‐to‐beat cycle length variation (% R‐R variation), which would be helpful to differentiate individual premature beats from normal variability . A recently published study suggests that normal % R‐R variation of falls between −4 and +4% of the preceding R‐R interval at HRs above 100/min.…”

Relationship between Resting and Recovery Heart Rate in Horses

“…The HRresting of the horses in this study did not depend on their age. Such a relationship has been reported previously [39][40][41], with the exception of Younes et al [42]. These discrepancies might be due to breed and age differences of the horses used in the studies.…”

Changes in heart rate and heart rate variability as a function of age in Thoroughbred horses

“…Heart rate variability has been applied as a method of assessing autonomic nervous activity in Thoroughbred horses as well as in humans and other animal species [ 6 , 7 , 9 , 10 , 15 , 16 , 17 , 18 , 19 , 20 , 23 , 25 ]. Although it has been reported that the response of HR variability to sympathetic beta-adrenergic blockade in Thoroughbred horses is different from that in other mammals, it has been shown that the magnitudes of LF and HF power reflect autonomic activity in Thoroughbred horses [ 9 , 19 ].…”

“…Although it has been reported that the response of HR variability to sympathetic beta-adrenergic blockade in Thoroughbred horses is different from that in other mammals, it has been shown that the magnitudes of LF and HF power reflect autonomic activity in Thoroughbred horses [ 9 , 19 ]. Many studies have investigated effects on HR variability of stress, effects of medications, responses of horses being transported, horses in pain, horses during training, etc [ 6 , 7 , 9 , 10 , 15 , 16 , 17 , 18 , 19 , 20 , 23 , 25 ]. It has also been reported that HR variability may reflect the degree of relaxation in horses immersed in a hot spring bath [ 7 ].…”