Utilisation of the time constant calculated from heart rate recovery after exercise for evaluation of autonomic activity in horses
- 1 August 2006
- journal article
- Published by Wiley in Equine Veterinary Journal
- Vol. 38 (36), 141-145
- https://doi.org/10.1111/j.2042-3306.2006.tb05530.x
Abstract
Heart rate (HR) recovery immediately after exercise is controlled by autonomic functions and the time constant (T) calculated from HR recovery is thought to be an index of parasympathetic activity in man.To investigate whether it is possible to evaluate autonomic function using the time constant in horses.Five Thoroughbred horses were subjected to a standard exercise test. Following pre-medication with saline, atropine and/or propranolol, the horses ran for 2.5 min at a speed of 8 m/sec at a 10% incline and T was calculated from HR after the exercise. Secondly, 7 Thoroughbred horses were then trained for 11 weeks and T and maximal oxygen uptake (VO2max) measured at intervals of 1 or 2 weeks. In 6 horses, T with atropine pre-medication was also measured before and after the whole training period. Furthermore, the HR variability at rest was evaluated by power spectral analysis at intervals of 3 or 4 weeks.Time constant was increased by atropine and/or propranolol pre-medication, decreased with the progress of training and inversely correlated with VO2max during training (r = 0.43, P<0.005). Parasympathetic blockade significantly decreased T only after and not before, the training; however, T was lower in post training than in pretraining, irrespective of parasympathetic blockade. On the other hand, parasympathetic activity at rest was attenuated and sympathetic activity became predominant following the training.Heart rate recovery is affected by sympathetic withdrawal and parasympathetic reactivation in horses and suggests that physical training hastened HR recovery by improving the parasympathetic function after exercise with aerobic capacity. However, the effects of other factors need to be considered because the training effect appeared on T even under parasympathetic blockade. The parasympathetic activity at rest is in contrast to that after exercise, suggesting that T does not reflect parasympathetic activity at rest.If demonstrated how HR recovery is controlled after exercise, its analysis will be important in the evaluation of physical fitness in horses.Keywords
This publication has 17 references indexed in Scilit:
- Comparison of Polar 810 s and an Ambulatory ECG System for RR Interval Measurement During Progressive ExerciseInternational Journal of Sports Medicine, 2004
- Parasympathetic Effects on Heart Rate Recovery after ExerciseJournal of Investigative Medicine, 2004
- Cardiac output measurements using sonomicrometer crystals on the left ventricle at rest and exerciseEquine Veterinary Journal, 1999
- Assessment of autonomic nervous function by power spectral analysis of heart rate variability in the horseJournal of the Autonomic Nervous System, 1996
- Vagally mediated heart rate recovery after exercise is accelerated in athletes but blunted in patients with chronic heart failureJournal of the American College of Cardiology, 1994
- Plasma norepinephrine and heart rate dynamics during recovery from submaximal exercise in manEuropean Journal of Applied Physiology, 1989
- Kinetics of heart rate responses to exerciseJournal of Sports Sciences, 1988
- Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exerciseJournal of Comparative Physiology B, 1988
- One-step N2-dilution technique for calibrating open-circuit VO2 measuring systemsJournal of Applied Physiology, 1981
- Faster adjustment to and recovery from submaximal exercise in the trained stateJournal of Applied Physiology, 1980