Electrocardiographic changes induced by physical exercise in the jumper horse

Modificações eletrocardiográficas induzidas pelo exercício físico no cavalo saltador

Electrocardiographic changes induced by physical exercise in the jumper horse

Modificações eletrocardiográficas induzidas pelo exercício físico no cavalo saltador

G. Piccione^I; A. Assenza^I; F. Fazio^I; E. Giudice^II; G. Caola^I

^IDepartment of Morphology, Biochemistry, Physiology and Animal Productions Faculty of Veterinary Medicine - University of Messina Polo Universitario dell'Annunziata Postal code 98168 Messina - Italy

^IIDepartment of Medical Sciences - Faculty of Veterinary Medicine - University of Messina

ABSTRACT

The authors conducted an electrocardiographic investigation on eight jumpers of Sella Italiana breed to evaluate cardiovascular changes associated with specific competitions. Electrocardiographic recordings were carried out using an electrocardiograph with a deflection of 10 mm/mV and a paper speed of 25 mm/sec. Recordings were conducted under the following experimental conditions: at rest, after warm up, after a jumping trial, and 15 and 30 minutes after the end of the trial. Significant reductions were observed in the duration of the P wave, of the P-Q interval, and of the R-R intervals immediately after the test. Significant elevations were observed immediately after the test in the range of the T and P waves of the heart rate. The observed changes can be attributed mainly to increase of the sympathetic tone connected with increase of heart rate necessary to satisfy the elevation of the cardiac range. These results are useful to plan and monitor specific training programmes.

Keywords: horse, physical exercise, training, electrocardiographic parameters

RESUMO

Realizou-se uma investigação eletrocardiográfica em oito cavalos saltadores de raça Sella Italiana para avaliar as modificações cardiovasculares associadas com competições desportivas específicas. O registro eletrocardiográfico foi realizado com eletrocardiógrafo digital de múltiplos canais com calibração de 10 mm/mV e velocidade de 25 mm/s. Registros foram obtidos nas seguintes condições: em repouso, durante o aquecimento, após uma sessão de saltos e 15 e 30 minutos após a sessão de saltos. Reduções significativas foram observadas na duração da onda P, do intervalo P-Q e dos intervalos R-R imediatamente após o teste. Elevações significativas foram observadas nos limites de variação das ondas T e P e da freqüência cardíaca. Essas modificações podem ser atribuídas primariamente à elevação da atividade simpática ligada à elevação da freqüência cardíaca necessária para o aumento do débito cardíaco. Estes resultados podem ser extremamente úteis no planejamento e monitoria de programas específicos de treinamento.

Palavras-chave: cavalo, exercício físico, treinamento, parâmetros eletrocardiográficos

INTRODUCTION

During the monitoring of variations and metabolic-functional adaptations resulting from sports activity, the parameters to be measured carefully are the ones affected by the effort of training. Although scientific research has led to the development of new instruments and methodologies for evaluation of functional abilities that favour performance, useful information can be obtained by traditional systems. In many cases, these systems can be further developed and, as a result, stereotyped methodological criteria can be avoided and useful information for the comprehension of the adaptation processes in the athlete can be gathered.

In the horse, athletic performance is a multifaceted entity that depends on numerous characteristic factors of each animal which make it more or less suitable for specific activities. A detailed study of the literature showed that numerous experiments have been carried out on jumpers concerning the influence of jumping, during a steep chase trial, on the behaviour of parameters such as haematic lactate, energetic and nitrogenous metabolites, and enzymatic and electrolytic activities (Art et al., 1990; Caola et al., 1991; Barrey, 1992; Cowalewsky et al., 1992; Piccione et al., 1995; Scribano et al., 1997). The results have been used to describe the various conditions and factors that influence competition results, that is to say, what is defined in sport science as "the performance structure" (Neumann, 1991). This includes both biomechanical and kinematical factors, meant as strength time adaptations, and energetic metabolic factors that result from training.

Metabolic adaptations of a general and specific type occur as training proceeds, specific adaptations being dependent on the type of effort required. Cardiovascular factors, in particular, are especially active in shaping adaptations on account of the fundamental role that they play in supplying oxygen to the muscles used during competitive activity. In the present study, an electrocardiographic investigation was conducted to evaluate the cardiovascular adaptations that occur during specific competitive trials in the athletic horse. The results of the investigation have potential application in the improvement of training programmes for jumpers.

MATERIALS AND METHODS

Eight jumpers (three females and five geldings) of Sella Italiana breed, average age 8 ± 2 years, clinically healthy and in training, were used. All the subjects took part in a steeplechase official trial. The trial covered a 350 metre course with 8 vertical fences varying in height between 1.0 m to 1.10 m and a gate. The course was covered by the horses in an average time of 49 minutes ± 4 seconds. Electrographic recordings were made on all the animals using an electrocardiograph with microprocessor (P80 3-channel Esaote Biomedica), with a deflection of 10 mm/mV and paper speed of 25 mm/sec. The Einthoven derivation system described by Steel (1963) was used for this purpose, with the electrodes placed 2.5 cm above the accessory bone of the carpus on the fore limbs and on the back of the distal tibial region, at about hock level in the hind limbs. The leads recorded were: I, II, III, aVR, aVF, and aVL. The electrocardiographic recordings were carried out under the following experimental conditions: at rest, after light warm up (15 min. of trotting), after the steeplechase trial, and 15 and 30 minutes after the end of the trial. The standard DII derivation was used for the measurements.

The following electrocardiographic parameters were measured on each recording: P wave duration and amplitude, P-Q interval duration, QRS complex duration, Q, R and S wave amplitudes, T wave duration, and Q-T interval duration. Then, corrected Q-T (Q-Tc), longest, shortest and average R-R interval, maximum heart rate, minimum heart rate and average heart rate were calculated. The corrected Q-T (Q-Tc) was calculated considering the average duration of the Q-T interval as referred to the normal frequency range.

Statistical elaboration of data was based on the average value of the results obtained. The data obtained under each experimental condition were treated as coming from a homogeneous sample group, as the intra-group variance was not significant. The statistical significances were also calculated using the Student t test for paired data, by comparing the parameters at rest with those recorded after warm up, and the parameters after warm up with the ones obtained under the other experimental conditions.

RESULTS AND DISCUSSION

Tables 1 and 2 show the average values of the electrocardiographic parameters expressed in their conventional units of measurement together with the standard deviations and the statistical significance under different experimental conditions during an official steeplechase in the eight horses.

Figures 1-5 show the progress of the electrocardiographic parameters studied under different experimental conditions in the eight horses.

On the basis of the results obtained we can affirm, firstly, that the increase or decrease in the parameters recorded in this experimental conditions can be attributed mainly to an increase in the sympathic tone connected to the increase in heart rate required to satisfy the increase in cardiac output resulting from physical effort. This adaptation seems evident from the marked increase in vagal tone, characteristic of athletes, manifested in this specific case in the relatively modest increases in heart rate after the jumping trial. Also, the fact that some variations in values are still present at the last recording carried out after the race, leads us to think that 30 minutes is not long enough for all the electrocardiographic parameters to return to their basal values.

The statistically significant variations in the main electrocardiographic parameters that were measured can be summarized as follows: As regards the P wave, the consulted texts would lead one to suppose that training does not seem able to bring about appreciable variations in duration, morphology and voltage of the atriogram (Beckner and Winsor, 1954; Mckeichnie et al., 1967; Nakamoto, 1969). However in this study, we encountered a decrease in the duration and a statistically significant increase in the amplitude of the P wave after the trial compared to after warm up. The increase in the P wave amplitude could possibly be attributed to an increase in the sympathic tone as has already been suggested by some authors (Schaub, 1966).

The QRS duration after training seems to be greater in the human athlete (Beckner and Winsor, 1954; Venerando and Rulli, 1974) and to be associated to a slowing down of the ventricular complex (Nakamoto, 1969; Venerando and Rulli, 1974; Venerando and Rulli, 1977). These variations were attributed to a greater duration of the depolarization of the ventricles caused by their increased dimensions, probably as a result of training. Moreover, it has been pointed out that the QRS complex variations tend to disappear during physical exercise, when the conduction speed of the impulse increases as a result of sympathic stimulation (Sugishita et al., 1983). In fact, the only statistically significant variation we recorded was a decrease in the QRS complex duration after the warm up compared to at rest, and this is in line with the articles mentioned.

The T wave is the most variable parameter of electrocardiographic tracing in the horse (Rose et al., 1979; Evans, 1989; Reimer, 1992). The commonest electrocardiographic abnormalities comprise inversion of polarity and increase in the T wave amplitude (Stewart et al., 1983), especially related to stress and to strenuous training (Rose et al., 1980). In fact, exercise provokes a change in the T wave polarity, probably on account of the direct influence of the coronary flow on ventricular repolarization (Holmes and Rezakhani, 1975). The T waves during exercise initially became more positive and showed increased amplitude. Changes in the waveform of T were of two types and what happened in an individual horse depended in part on whether the resting ECG was classified as normal or abnormal, and in part on the final heart rate developed during galloping exercise. In some horses, the ECG passed through a phase in which the T waves were tall, positive, narrow and peaky. Moreover, it has been observed that under strain this wave becomes wider and more pointed, exceeding, at times, the QRS complex voltage which precedes it (Steel et al., 1976). What has been reported is not in agreement with the results of this study, where the duration and the amplitude of the T wave present statistically significant increases 15 and 30 minutes after the end of the trial compared to at rest and immediately after the trial.

The influence of training on the correct Q-T interval durations for the heart rate (Q-Tc) in the human athlete is not univocal: according to some authors, the interval duration differs in the athlete and in the untrained subject (Beckner and Winsor, 1954; Smith et al., 1964) whereas, according to others, such a difference is not apparent (Hanne-Paparo et al., 1976; Palatini and Sperti, 1984; Palatini et al., 1987). The results obtained in this research show a statistically significant increase 30 minutes after the end of the trial compared to after warm up, immediately after the trial and 15 minutes after the end of the trial. These variations are probably caused by an increase in the neurovegetative tone (Schaub, 1966).

Heart rate in the horse at rest is generally between 25 and 50 beat/min. With a less than maximum work load, there is a linear correlation between heart rate and speed and between heart rate and consumption of oxygen in all horses. However, the real heart rate recorded in a horse at the trot or at a slow canter can present extreme variability due to age, to fitness and to health conditions. At the start of slow-speed exercise, the heart rate can fluctuate for some minutes before becoming stable: it rises quickly at the start of exercise and then decreases in the following minutes according to emotional state or to physiological phenomena. The maximum heart rate (HR_max), that is, the highest rate that can be recorded during physical exercise, is comprised between 215 and 250 beat/min at a gallop. In this study, after the jumping trial a maximum heart rate (HR_max) of 63.5 beat/min was recorded. The relatively low values recorded immediately after the trial could be attributable both to the relatively low strength required for this type of competition and to the degree of training of the tested animals, which present a prevalence of the vagal tone as illustrated by the slight increase in heart rate after exercise and by the low value of the R-R intervals (Higgins,Wright, 1995).

CONCLUSIONS

In conclusion, results could contribute to a definition of cardiovascular adaptation during physical exercise in the jumper, which is extremely useful in planning and monitoring specific training programmes.

Recebido para publicação em 21 de março de 2002

Recebido para publicação, após modificações, em 13 de março de 2003

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Publication Dates

• Publication in this collection
  12 Nov 2003
• Date of issue
  Aug 2003