Why is it necessary to give a horse a holiday? For an equine athlete to maintain peak fitness, their conditioning program must be evaluated & continually adjusted. Constant exercise at suboptimal intensities can limit the rate of adaptation, whilst constant exercise at maximum intensities may contribute to overtraining (Hodgson & Rose, 1995). Back in the day (wow I sound old) the horsewomen & men used to say their horse was stale or “sour” or the horse was “girthy. If your horse started to act tired, cranky, or exhibits a decreased appetite &/or performance, your horse might be fatigued & need some time off from both training & competition. “Active” rest, not to be confused with rest not due to an injury/sickness, can be in the form of turnout or hand walking & will give a horse time to recover from overtraining. By definition, signs of overtraining syndrome should persist after ≥2 wk. rest or reduced activity. A less severe form of overtraining syndrome is termed “overreaching”, which is also a syndrome of poor performance & fatigue, but recovery occurs within 1–2 wk. after a reduced workload (McGowan & Whitworth (2008). So just what is overtraining (OT)? Overtraining is a significant cause of poor athletic performance in both human & equine athletes. In humans, overtraining syndrome has been defined as an imbalance between training & recovery manifesting as a syndrome of chronic fatigue & poor performance accompanied by physiological & psychological changes (McGowan & Whitworth (2008)). OT is a loss of performance ability in the horse despite the maintenance of or, an ever increasing amount of training effort. For example; you are working your horse & you find you are needing more & more time to settle your horse before they go into a dressage test, where before it only took 40 minutes of work & now it takes over an hour of work to settle the same horse. So when overtraining ensues, a horse’s conditioning program must break or be reduced for a variable period of time in order for the horse to recover. Overtraining syndrome was first reported in Swedish Standardbred trotters. This was based on observations of horse’s with signs of fatigue & poor performance combined with weight loss, loss of appetite, and signs of psychic stress, including tachycardia, nervousness, muscle tremor, sweating, and diarrhoea. In the study the horses appeared to develop an extreme form of overtraining associated with red cell hypervolemia & adrenal exhaustion that may be similar to parasympathetic overtraining seen in people. In studies, a milder form of overtraining syndrome had been reproduced, without any evidence of red cell hypervolemia or adrenal gland exhaustion. However, the syndrome was associated with a decrease in the plasma cortisol response to intense exercise, suggesting overtraining is associated with dysfunction of the hypothalamic-pituitary-adrenal axis. Recent research has shown overtrained horses have altered growth hormone activities, with an increase in the normal pulsatile growth hormone activity overnight, plus altered glucose metabolism (McGowan & Whitworth (2008). Overtraining syndrome should be suspected in horses with evidence of sustained decreased performance in association with one or more physiologic or psychological (behavioural) signs. Whilst no single physiologic marker is able to identify the OT syndrome, signs in horses may include decreased body weight, increased heart rate during exercise, and decreased plasma cortisol response to exercise, and increased muscle enzymes or γ−glutamyl transferase concentrations. Behavioural signs are a consistent and early marker of overtraining syndrome, and development of behavioural scores to assist in early detection of overtraining syndrome in horses is warranted. What are the concerns with overtraining? A horse’s reserve blood is stored in the spleen. This is usually ‘bad blood’ because it has a higher viscosity than the blood found in normal circulation. This is because the stored red blood cells are stiffer and spikier than normal blood cells. Like pieces of grit flowing through tubes, the stiff & spiky blood cells can damage the inner lining of blood vessels & due to their higher viscosity, they can also increase systemic blood pressure. How many of a horse’s reserve blood cells are released into circulation actually depends on how hard the horse is working. Research shows the packed cell volume (PCV, or haematocrit, Hct), percentage of blood made up of red blood cells, increases together with the speed of the exercising horse. This usually occurs until the PCV or Hct. reaches approx. 60-65% during exercise bout (Persson, 1983). In other words, during the exposure time (time a horse is trained), the extent of how much thicker & stickier a horse’s blood gets will depend on how hard a horse is trained. The intensity of training plays a factor in determining the degree of damage the blood causes to the horse’s cardiovascular system. Furthermore, horse’s undergoing high-intensity exercise can lose ~ 10% of the plasma vol. in their blood through sweat & internal fluid shifts, which concentrates the blood (McKeever, et al., 1993; Muñoz, et al., 1999). What is detraining in horses? Detraining is the sudden cessation of a conditioning program due to perhaps sickness or injury. During this time, a horse experiences a rapid loss of physiological training adaptations. Changes in muscle occur in two to four weeks, followed by cardiovascular & bone changes. Decrease in muscle size & strength occur in the shortest amount of time. Oxygen uptake & ventilation capacity decreases within three weeks of detraining (Hodgson & Rose, 1995). Then the performance horse experiencing long layoffs due to either sickness or injury must begin re-training slowly & carefully to prevent a relapse (Hodgson & Rose, 1995). References: 1. Persson, S., Evaluation of exercise tolerance and fitness in the performance horse. Equine Exercise Physiology, 1983. 1: p. 441-457. 2. McKeever, K.H., et al., Role of decreased plasma volume in haematocrit alterations during incremental treadmill exercise in horses. Am J Physiol, 1993. 265(2 Pt 2): pp. R404-8. 3. Muñoz, A., et al., Locomotor, cardiocirculatory and metabolic adaptations to training in Andalusian and Anglo-Arabian horses. Res Vet Sci, 1999. 66(1): pp. 25-31. 4. Satué, K., A. Hernández, and A. Muñoz, Physiological Factors in the Interpretation of Equine Haematological Profile, in Haematology – Science and Practice, C.H. Lawrie, Editor 2012, InTech: Janeza Trdine 9, 51000 Rijeka, Croatia. pp. 596. 5. Muñoz, A., et al., Dehydration, electrolyte imbalances and renin‐angiotensin‐aldosterone‐vasopressin axis in successful and unsuccessful endurance horses. Equine Vet J, 2010. 42: pp. 83-90. 6. Lindner, A., et al., Effect of Conditioning Horses Once, Twice, or Thrice a Week with High-Intensity Intermittent Exercise on V4. J Equine Veterinary Science, 2011. 7. McGowan C M and Whitworth D J (2008). Overtraining syndrome in horses. Comparative Exercise Physiology, 5, pp. 57-65.
Posted on: Mon, 26 Aug 2013 03:00:37 +0000
Trending Topics
Recently Viewed Topics
© 2015