Even though they are prepared to take on the effort of racing, horses can feel tired which impacts their results. Several factors can induce fatigue, such as a significant decrease in energy reserves, muscular fatigue, the accumulation of lactic acid in the muscle, etc…
In addition, the cardio-respiratory system is also challenged in order to continue to ensure the body’s supply of oxygen, especially to the muscles: the heart rate then remains very close to its maximum for a significant period of time. As the race progresses, depending on the distance, horses adopt various locomotor strategies to optimize their efforts. These considerations can help determine the orders to give to the jockey on acceleration strategies during races.
How do stride length and stride frequency change during the race? Are there any differences in locomotion depending on the distance of the race? How do you spot a tired horse thanks to his locomotion?
1- How do horses adapt their locomotion during a race?
Maintaining a high stride length requires an efficient cardio-respiratory system, especially at canter where breathing follows the same rhythm as the strides (breathing in when in the air, breathing out during the three steps on the ground). When a horse’s pace increases, i.e. when the frequency of his strides accelerates, his breathing follows the rhythm of the strides. In long races, it is extremely difficult to maintain a high pace throughout the race while keeping a sufficient amount of air. This makes it necessary for the horse to maintain a very high breathing rate which can cause premature shortness of breath.
To maintain a high speed over long distances, the horse must rely on the size of his strides. A large stride frequency is less demanding on the cardio-respiratory system (longer time in the air, thus longer time to breathe in), nevertheless, the muscles must be prepared for this effort as they are more solicited in terms of power and energy. In the last 200m, if the horse is still able to do so, he will try to sprint by increasing his pace and stride length. This ideal situation may not be respected in a race, as the horses have to adapt to the field, the speed and their place in the group at all times.
When there is a sudden change of pace during the race or to reposition, horses tend to adapt to this new speed by changing their pace as it is much quicker to increase or decrease the frequency of the strides than to increase their size. This is why the best sprinters are horses that can easily modulate their pace.
On the following example (from harness races in New Zealand), it is possible to study the locomotion of the trotters who finished in the top 3 on races of 1950, 1980 and 2000m. The average stride length and stride frequency for each 200m interval have been plotted. Thus, we notice that the horses decrease their stride frequency and stride length after the start: once well positioned, they keep their speed, to strongly increase their stride frequency in the last 400m in order to take the advantage. On the other hand, if they are able to increase their pace at first, they are not able to maintain it until the end: after having accelerated, they rely on their stride frequency to ensure a place at the finish. Variations in stride frequency during the race are linked to the turns.
2- A locomotor strategy for each distance
Depending on the distance of the race, the speeds will be different, as well as their evolution (see our Speed white paper to know more). Over short distances, horses must give their maximum and accelerate very strongly in the last 200m. Longer races require a more thorough management of the horse’s resources in order to conserve its strength until the end of the race. The distance of a race influences the speed of the race and therefore the locomotion. However, at the same speed, the winning locomotor strategy differs according to the distance. The last 200m in particular are very much affected by the distance of the race.
This horse is a good example, he ran and won on 1980m, 2600m and 3200m in harnessed trot races. Here is the table showing his average speed, his average stride length and his average stride frequency according to the distance of the race.
As expected, speed decreases as distance increases, resulting in a decrease in stride frequency and average maximum rate (data is from a harness racing database from New Zealand).
In order to be able to compare the locomotion of two horses that have run on different distances, it is not possible to compare only their maximum stride length or stride frequency. Since short races are faster, the horse that has run shorter distances will necessarily have a higher maximum stride length and maximum stride frequency than the other. On the other hand, comparing locomotion with a fixed speed in the two races gives us more interesting information about the locomotor profile of these horses. As the trio of speed, stride frequency and stride length are related, by fixing the speed (e.g. 60km/h in canter and 50km/h in trot), we obtain an objective measure of the locomotor difference between both racing distances.
This allows us to observe that the more the distance increases for the same speed, the more the horses tend to make long strides by restricting their pace. As we have seen, this relieves the strain on their cardio-respiratory system, which is already strained by the intensity of the effort. In addition, it is logical that in a short race the pace is higher. Reaching a maximum stride length requires more time, so over short distances it is more efficient to rest on a fast pace in order to reach a high speed. This speed is reached more quickly and gives the horse an advantage to win. These considerations are only valid for the race as a whole, and are no longer valid by focusing only on the finish.
Thanks to a database of 150,000 lines, the Arioneo team has traced the average stride frequency and stride length of horses classified in harnessed trotting over certain distances. In order to be able to compare, the locomotion used is taken at 50km/h.
Between 1600m and 3200m the pace decreases by 7% while the stride length increases by 7%. As expected, the stride frequency decreases with distance to relieve the cardio-respiratory system while the length increases to maintain a consistent speed.
As for the gallop, this table summarises the average stride frequency and stride length of the gallopers at 60km/h according to the running distance. It can be noticed that here again, the average stride frequency decreases as the distance increases, contrary to the stride length which increases with the distance.
It therefore appears that horses with high stride frequency would tend to win over shorter distances and horses with high stride length over longer distances.
The running distance affects the finish. Depending on the length, the locomotion in the last 200m is therefore clearly different. During a long race, the muscles are often tired from the effort they have put in and some horses produce lactic acid, a waste product which diminishes their performance and forces them to reduce their stride length in order to relieve their muscles. Some can no longer increase the size of their stride in the last 200m and are sometimes even forced to reduce it. In the best horses it is possible to accelerate by only increasing their pace as long as their cardio-respiratory system is still able to adapt to the effort required. On the contrary, we have seen that over very short distances, horses significantly increase their pace as well as their stride length during the last 200m.
We have therefore drawn the same graphs as before over 3200m for the horses having finished in the first 3. This allows us to observe:
1- the differences between their strategy on 1980m and on 3200m
2- the strategy they use in order to finish and win over 3200m
Here too, we observe a decrease in pace after the start of the race: once placed, the horses save their energy. During the race, they keep their pace almost constant: the slight variations are due to the turns, which is also seen in the stride length, which varies more. At the 800m, they harden the race pace as shown by the sudden increase in stride frequency. Although the stride length is not yet modified, it still retains a high value. Finally, in the last 200m, the stride length increases sharply while the stride frequency collapses. Horses therefore wait much longer to increase their stride length as their muscles are more tired than in a fast race. The race pace, before the last 600m, is only slightly higher: the difference between the horses is at the finish where only the fittest horses hold the stride length. Again, an increase in pace precedes an increase in length for the finish.
The length of the race influences the pace and the stride length selected by a horse. As tiredness appears, the horse adapts his locomotor strategy in a global way during the race but also during the last 200m. Tiredness is therefore the cornerstone of locomotion adaptation for racehorses.
3- What is the impact of fatigue on the locomotion of a horse in a race?
In addition to the changes in stride length and stride frequency that occur depending on the duration and intensity of the run, other parameters are also affected by the effort. If a fatigue that is more related to the horse’s cardio influences almost exclusively its stride length, a more muscular tiredness will induce other adaptations which can be the cause of injuries.
When the muscles accumulate too much organic waste (including lactic acid in particular), they lose efficiency. The lack of oxygen deprives the brain of a precious resource. Horses are no longer able to maintain a regular stride because the nervous system is no longer sufficiently oxygenated to continue to regulate the body. They are subject to stumbling or erratic footwork, as the muscles no longer catch up as well with the irregularities of the ground. The limbs can then become slightly out of synchronisation. This will result in a decrease in regularity and symmetry in trotters.
In order to distribute their effort, it is common to see gallopers change their feet. In fact, galloping on the right side of the track requires more effort from the right diagonal than the left. The muscles on this side are then more under stress. The horse changes foot as the race progresses in order to rest the two diagonals successively and to create a uniform fatigue on the muscles of its two front legs. It is rare for a horse to run the whole race on the same galloping foot. Moreover, horses can inhale only during the projection phase of the gallop. When changing feet, this projection phase is slightly longer. Therefore, a change of foot provides the necessary breath of air to mark a cut during the race. A change of foot is an opportunity to provide a surplus of oxygen reducing the cardio-respiratory fatigue.
The horses adapt their pace and stride length as the race progresses. A high stride frequency allows you to reach a maximum speed quickly but puts a strain on the heart, while a high stride length makes the muscles work harder and saves breath. Over long distances, horses tend to prefer a wide stride to save themselves for the final sprint. However, in long races, it is not uncommon for horses to be unable to maintain their stride length. With fatigue, the regularity of the strides decreases as well as their length and/or pace. Changing galloping foot is an opportunity to inhale, giving an oxygen boost to the muscles, and to balance muscles employed, to go stronger and accelerate.