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Focus on Muscle Power in the Horse

Do you know what happens within your horse’s body while training? A lot more happens than you might think. In this blog, we explain how the horse’s muscles work, where they get their energy from, and why horses get tired?



Summary

The muscle of a horse needs glucose and oxygen to contract.

· A light training utilizes mostly an aerobic pathway, an intensive training mostly an anaerobic pathway.

· The brain signalizes fatigue through organs or muscles when they are in danger.


How do muscles work?

In order to move the body, the horse needs to contract its muscles. To generate the power needed for this, the muscles need energy. A muscle generates energy by using glucose and oxygen, if it is available. In normal metabolic processes, cells respire in order to release energy to fuel their living processes. The respiration can be aerobic, which uses glucose and oxygen, or anaerobic which uses glucose only. This is referred to as aerobic or anaerobic metabolism, respectively. During the course of a training, the pathway changes depending of the amount of oxygen and glucose that is available.

We will discuss four stages of training:

  1. First explosion.

  2. Light training.

  3. Intensive training.

  4. Brain fatigue.

1. First explosion

If a horse suddenly has to run, for example, because it spooks in the field, the muscle first uses the glucose that is stored in the muscle. There is no oxygen at first, so the muscle initially uses the less efficient, anaerobic pathway.

This is why it is important to start with ‘warming-up’ in regular training program. This allows the body to prepare the muscle and increase the blood flow to the muscles that delivers extra oxygen.



2. Light training

In light training, after warming-up there will be enough oxygen transported to the muscle to allow for the highly efficient aerobic metabolism of glucose (see Figure above). A horse can keep this up for a long time. In, for example, a two-hour training in walk, the heart-rate of your horse stays under 100 beats per minute.

The heart-rate is a good indicator for the demand for oxygen in the muscle.

The more oxygen is required, the more blood needs to be pumped to the muscle to bring the oxygen, the higher the heart-rate will be.

3. Intensive training

As a training becomes more intensive, the muscles will first run out of oxygen. On average, this happens at a heart-rate of around 180 beats per minute. This would be, for example, when you ride in canter for six to eight minutes or you ride uphill, or on a rough terrain. When a specific muscle runs out of oxygen varies greatly between horses and depends upon the training level of the horse.

The fitter the horse, the better it is able to bring oxygen to the muscles, and the longer it can rely on the more efficient aerobic metabolism.

If the muscle runs out of oxygen, it will switch to the less efficient anaerobic metabolism. It can now only generate two energy molecule instead of 36. In this process, extra acid (H+) is produced, in the form of lactic acid. This causes acidification and fatigue of the muscle. It is a misconception that lactate is the cause of acidification, lactate actually has many benefits for the muscles in this stage.

What does lactate do?

  • Lactate helps against acidification.

  • Lactate functions as a signal substance.

  • Lactate ensures more energy.

  • During intensive exercise, lactate functions as an energy source for organs, like the heart.

  • After training, it takes an average of three hours for the body to break down the lactate.. Light training



Figure 1. A research in 36 human cyclers showed no relationship between the onset of fatigue and lactate concentrations in the blood. Some athletes could keep on cycling way beyond the anaerobic threshold of 4 mmol/L blood lactate. This indicates that the blood lactate measuring is not a good tool to compare fitness levels between athletes or horses.

4. Fatigue in the brain

An increasing body of research confirms that the muscles probably do not cause the onset of fatigue and are most likely not the limiting factor in performance. Long before the muscles truly run out of glucose and have to utilize lactate as their source of energy, the body sends warning signals to the brain. A lack of oxygen, overheating and a drop in glucose in the blood are all signals to the brain to slow the body down. This prevents the body from overtraining or from injuries occurring, and is vital for the survival of the body. It is very hard for any athlete to ignore these signals and keep training passed the barriers of ‘central fatigue’ in the brain.

Keeping the brain motivated in training is a very important aspect of training. Creating a high standard of wellbeing and a positive emotional state will translate directly into better performance. And, as horses are not motivated by medals as humans are, other motivational rewards need to be in place, and applied with perfect timing in training. Horse are very sensitive to pressure release or motivational stroking.

References:

· (In Dutch) Burgerhout, W. G. (2008) Afscheid van melkzuur, deel 1 27: 322. https://doi-org.has.idm.oclc.org/10.1007/BF03077607

· (In Dutch) Burgerhout, W. G. (2009). Afscheid van melkzuur, deel 2. Stimulus, 28(1), 37–49. https://doi.org/10.1007/s12491-009-0005-8

· (In Dutch) Burghout, W. (2017). Visies op vermoeidheid Deel 1: Waarom houdt dat verzuren maar niet op? Sportgericht, 71(5), 20–22.

· Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2014). Biology: A Global Approach. “In 10.5 Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen.” (pp. 253–256). Essex: Pearson Education Limited.

· Cairns, S. P. (2006). “Lactic Acid and Exercise Performance.” Sports Medicine, 36(4), 279–291. https://doi.org/10.2165/00007256-200636040-00001

· Gladden, L. B. (2004). “Lactate metabolism: a new paradigm for the third millennium.” The Journal of Physiology, 558(1), 5–30. https://doi.org/10.1113/jphysiol.2003.058701

· Hall, M. M., Rajasekaran, S., Thomsen, T. W., & Peterson, A. R. (2016). “Lactate: Friend or Foe.” PM&R, 8(3S), S8–S15.

https://doi.org/10.1016/j.pmrj.2015.10.018

· Hinchcliff, K. W., Kaneps, A. J., & Geor, R. J. (2008). “Equine Exercise Physiology: The Science of Exercise in the Athletic Horse.” Edinburgh: Saunders/Elsevier.

· Noakes, T. D. (2004). “From catastrophe to complexity: a novel model of integrative central neural regulation of effort and fatigue during exercise in humans.” British Journal of Sports Medicine, 38(4), 511–514. https://doi.org/10.1136/bjsm.2003.009860

· Nybo, L., & Rasmussen, P. (2007). “Inadequate Cerebral Oxygen Delivery and Central Fatigue During Strenuous Exercise.” Exercise and Sport Sciences Reviews, 110–118. https://doi.org/10.1097/jes.0b013e3180a031ec

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