To better analyse heart rate, recovery and make an objective diagnosis of the fitness of your horses, it may be relevant to dive into the physiological mechanisms at work when the athletic horse is training. Arioneo’s data analysts give you a few notions of physiology of the equine athlete.
The body and especially the muscle cells need energy in order to produce a physical effort. This source of energy is called adenosine triphosphate or ATP. The body has a very small reserve of ATP present in the muscle cells. Thus, the necessary energy must be generated continuously to meet the body’s demand. We can distinguish 3 main production mechanisms that will be used depending on the intensity and duration of the effort.
At the beginning of an intense and very short exercise, a small reserve of energy stocked in the muscle is used. However, this stock is small and does not provide sufficient energy when the effort lasts more than a few seconds.
For longer exercises, two other means of energy production are used depending on the amount of energy required.
At low speeds, the body mainly uses the deterioration of fat by oxygen to produce energy. This mechanism is highly efficient, being an almost inexhaustible source and does not produce lactic acid. We are talking about an aerobic process. However, it is slowly implemented by the body and the amount of energy delivered is limited by the amount of oxygen available. The amount of oxygen assimilated depends on various parameters such as the volume of the lungs, the breathing rate, the volume of the heart or the efficiency of cardiac contraction. For example, the amount of available oxygen is limited by the maximum heart rate (FCmax), which is specific to each horse and varies little with age and training. The maximum heart rate is not an indicator of fitness. Once the maximum heart rate has been reached, the volume of oxygen assimilated can hardly be increased.
When the effort becomes more intensive, the fats cannot produce energy quickly enough. The body will then degrade the glucose and glycogen (sugar) supplies that are stored directly in the muscles, without using oxygen. Unlike fat, glycogen is present in limited quantities in the body, but its breakdown is quick and produces more energy. This process is called anaerobic. Nevertheless, it produces a waste product: lactic acid. If there is not enough oxygen in the blood to eliminate it, the lactic acid accumulates in the muscles, degrades the quality of contraction and can cause pain: the effort must be limited in time.
Effort zones are generally defined in terms of HRmax, as follows:
- Up to 70% of the HRmax: the body uses fat as its main mean of production.
- Between 70 and 80% of HRmax: fat continues to be consumed but the difference is made up by glycogen. The body is still able to supply enough oxygen to eliminate lactic acid. We can talk about alactic anaeroby.
- 80% to 90% of the FCmax: from this threshold the body starts to accumulate lactic acid. The more lactic acid it accumulates, the less effective muscle contraction is. This threshold is associated with a speed called MAV (Maximum Aerobic Velocity) which is the maximum speed that can be reached without producing lactic acid. Above this threshold, the body enter the lactic anaeroby phase.
- At 90% to 100% of the FCmax: the body accumulates a lot of lactic acid. It becomes painful for the muscles and the body to support the exercise.
Thanks to training, the body can optimize the processes of energy creation and consumption. At a given speed, it needs less energy and therefore less oxygen, which leads to a lower heart rate at that speed. A trained horse will “push its MAV threshold”, i.e. he will be able to run faster and longer without producing lactic acid. In addition, a horse who regularly trains in its anaerobic zone (beyond its threshold), will better tolerate lactic acid. The effects on the functioning of his muscles will decreased. However, these sessions are very demanding and must be carried out with care.
It should be noted that at the beginning of a training, all three sources of production begin to work. The cycle using fats is the slowest to be implemented, but it is the one offering the best performance. This is why warm-up is essential to allow the processes to initiate. It should also be noted that after exercises above the MAV threshold, the heart rate generally remains high in order to provide the oxygen necessary to eliminate lactates: it is as if the body had contracted an oxygen debt that is compensated with a HR staying at its maximum even after the speed has decreased. A rapid recovery is often the sign of a horse that produces little lactate during exercise.
A CONCRETE EXAMPLE
Here are two examples of hard work monitored by Equimetre. On the first one, the horse is very fit and the HR start decreasing as soon as the speed does. On the second one, we can see the oxygen debt at the end of the speed work with the HR staying at the HR max for a little while after the speed decreased, waiting for the body to eliminate the lactates.
The practice of active recovery or the performance of low-intensity exercise which uses the aerobic cycle will contribute to the degradation of the lactates by supplying oxygen to the muscle. This article about the recovery will give you some information about how active recovery can help the horse recover from an intense exercise.