The objectives of the present study were to investigate the effects of Aquatraining of horses (aqua-treadmill exercise; treadmill manufactured by Equitech - L.u.S. Equipment, Warendorf, Germany) on selected blood parameters [lactic acid concentration (mmol/l), haemoglobin content (g/l)] and on heart-rate variability (HRV) [heart rate (beats per min; b.p.m.), standard deviation of all NN-intervals (SDNN; ms), normalized power of the low and high frequency band (LFnorm, Hfnorm; au), % recurrence, % determinism and ratio(corr)]. Seven horses performed six exercise tests with different work loads (walking (x = 1.56 +/- 0.08 m/s) and trotting (x = 2.9 +/- 0.13 m/s): dry, water above the carpus and water above the elbow). The standardized test-protocol was: 5 min warm-up at walk while the water was pumped in, followed by the 20-min exercise period at walk or trot, followed by a 5-min walk while pumping out the water. Blood samples were taken prior to each test at rest in the stable, as well as exactly 5 min after the end of the 20-min exercise period. Electrocardiograms were recorded during rest and the 20-min exercise period. Compared to rest, neither the chosen velocities, the two water levels, nor the dry tests led to a significant increase of the lactic acid concentration in any horse. The haemoglobin content showed a significant increase as a result of exercise. Significant differences could be found between the heart rates at rest and the six exercise tests and between the mean of the levels 'walking' and the mean of the levels 'trotting'. An exercise-induced change of HRV was characterized by a decreasing SDNN, a significantly higher LFnorm (sympathetic influence) combined with a significantly lower HF(norm) power (parasympathetic activity) and a rising degree of order (significantly higher % determinism and nearly unchanged % recurrence) and stability (significantly rising ratio(corr)) of the recurrence plot. In conclusion, the used training-protocol for aqua-treadmill exercises only represents a medium-sized aerobic work load for horses, but the different levels of burden were indicated especially by changes in HRV.

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Summary The heart rates of 19 Thoroughbred racehorses have been continuously recorded during racing. Before the start, heart rates are highly variable due partly to emotional influences. In the starting stall immediately prior to the race, frequencies averaging 132 ± 18 were recorded. This corresponds to an anticipated rise in heart rate of 50 per cent of the total rise recorded during the race. Maximal heart rates reached an average of 223 ± 11 (coefficient of variation 5 per cent). Résumé Les rythmes cardiaques de dix neufs chevaux de Pur Sang ont été enregistrés de façon permanente durant la course. Avant le départ les rythmes cardiaques sont très variables, notamment sous l'influence de facteurs émotionnels. Dans les stalles de départ, immédiatement avant la course des fréquences de 132 ± 18 ont été enregistrées. Ceci correspond à une élévation anticipée du rythme cardiaque, de l'ordre de 50% de celui enregistré durant la course. Le rythme cardiaque maximum atteint une moyenne de 223 ± 11 (coefficient de variation 5%). Zusammenfassung Die Herzschlagfrequenzen von 19 Rennpferden Englischen Vollbluts wurden kontinuierlich während der Rennen aufgezeichnet. Vor dem Start zeigten sich ausgeprägte Variationen, die zum Teil emotionellen Einflüssen zuzuschreiben waren. In den Startboxen wurden unmittelbar vor dem Rennen Frequenzen von 132 ± 18 gefunden. Dieser Befund stimmt mit einem vorausgesehenen Anstieg der Herzschlagfrequenz um 50% des totalen Anstiegs während des Rennens überein. Die maximalen Herzschlagfrequenzen erreichten einen Durchschnitt von 223 ± 11 (Variationskoeffizienz 5%).

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