Exercise Testing in Equine Athletes

By Celine Abela, Werner Bouwer, Jodine Koen.

Introduction

Athletic horses are known to compete, worldwide, in varying disciplines of equine sports. These competitions require tremendous amounts of exercise and effort which for the horse, carries physiological, pathological and physical risks. Consequently, athletic horses need to maintain optimal condition, as to avoid injury and perform at their best ability. Hence, multiple tests have been developed to identify, alleviate or prevent potential health problems as well as evaluate the health and condition of these horses.

Two main kinds of exercise testing will be discussed, both possessing individual advantages and disadvantages. These include treadmill laboratory tests and field testing. Clinical laboratory tests are usually favoured by veterinarians due to standardisation, yet they do have some disadvantages compared to field tests. Field tests better mirror the natural work environment of the horse, moreover, multiple parameters may be assessed with these exercise tests.

Treadmill testing

“The main challenges in performing field tests lie in the ability to truly standardise them” (Allen et al, 2016). That is where Treadmill testing comes in as it is a controlled way of testing for parameters in horses. Having the environment standardised will eliminate external or confounding, and so will not be able to influence the test. These exercise testing are carried out on more advanced equipment; this allows for finer readings and a vast area of data, that can be collected. There can be multiple speeds or inclinations used on the treadmill to better suit the test required. Moreover, in this situation, the horse is immediately, and more easily accessible, so that if any samples are needed right after the exercise test, such as blood drawing, they can be done.

Treadmill exercise testing has many disadvantages in many areas. “Treadmill exercise testing can be difficult to integrate into the management of an athletic horse” (Couroucé-Malblanc and Erck-Westergren, 2016). It does not reflect the natural environment of the horse and where it works or competes. Apart from the obvious terrain difference, there are also more stressors in the field which are not accounted for in the laboratory. Also, the stride and gait of the horse differ between field and treadmill, as even if the speed of gallop used on the treadmill is the same as the race track the frequency of the stride does not match. Many studies comparing the results of heart rate and plasma lactate show significant differences between tests in the laboratory environment and the field. Therefore, even though the tests are repeatable they do not reflect reality in most cases. Another factor to take into consideration is the budget and willingness of the owner. These laboratory tests used expensive machinery and equipment, which makes the cost of the test on the whole very high. Moreover, treadmill exercise testing requires a lot of time. This is because the horse needs to be acclimated to the machinery and environment, and also trained to use the treadmill. Proper conditioning to the equipment can lead to the most serious disadvantage of the treadmill, as this can cause injury to the horse.

Yet the necessity of the horse to be acclimatised has been debated multiple times according to Couroucé-Malblanc and Erck-Westergren (2016), as some performance testing laboratories do this and others don’t.

Field testing

The Field test is an exercise method that is used in the evaluation of various horses. Field tests are necessary to recreate the exertion that occurs during training and competition. Understanding the physiological effects of the effort that the horse experiences in each discipline, allows for improvement in the training and conditioning processes. “Biological characterization is key in determining the performance indices used to identify physical status” (Allen et al, 2016). Horses used in field riding are exposed to various conditions (weather, topography, etc). Therefore, it is very important to test the physiological change in the horses caused by the field training as shown by Ok-Deuk and Yong-Soo (2017).

The Major advantage of field testing is that the test can be conducted in an environment that is similar to the actual situation. Present studies also show that field tests could provide useful physiological parameters, such as VLA4 (the velocity at which blood lactate reaches 4mmol/L), V200 (the velocity at which heart rate reaches 200 beats per minute), and even V160 (The velocity at which the heart rate reaches 160 beats per minute). The surfaces, gaits, and speeds in a field test are more accurate, and more closely aligned to what the demands are, that the horse faces during exercise in genuine conditions. Field tests also account for the effect of the rider and may be performed without the need for sophisticated equipment.

The field test can be incorporated into the daily routine as a normal gallop session, as shown in figure 1. The field test does not only give the researcher’s information, but it also gives the rider the ability to assess the horse’s fitness status, such as VLA4, V160, and V200, and it can discriminate horses of different races and fitness levels. In addition, this test can be completed regularly alongside a follow up medical examination to detect early physiological abnormalities. During treadmill testing, the horse needs to be acclimatised before to the treadmill before the actual test can be completed. With field testing, no prior acclimatisation is needed to perform the test as told by Fraipont et al (2012).

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Figure 1 Rider trotting horse.

Parameters tested

Heart Rate

Heart rate (HR), or the frequency of beats per minute, is an important parameter that is tested in equine athletes using exercise testing. This is used to determine the progression of training and also the condition of the horse's heart. HR response to exercise is measured using electrodes fastened to a thoracic girth strap which is placed under the saddle (Couroucé-Malblanc and Erck-Westergren, 2016). These electrodes are connected to a transmitter which transmits the information wirelessly to the receiver which may be on the saddle, rider or the girth in the case of figure 2. This may be done on a treadmill or in the field, however on the treadmill it may not be as accurate.

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Figure 2 Horse being lunged by rider with electrodes attached on the girth.

The HR is usually paired with other factors, including speed. The test procedure consists of multiple steps, where the horse needs to run at different speeds at equal intervals, with a small pause or walk in between. This allows the recording of a graph, such as figure 3, of heart rate against speed. From this graph, the V200 may be calculated. The HR response to exercise is linear between 120 and 210 bpm (Couroucé-Malblanc and Erck-Westergren, 2016).

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Figure 3 Mean heart rate ± SE, as a function of velocity for yearling (■), two-year-old (□) and adult (●) Thoroughbred horses exercising on a treadmill set at 6 degrees; Yearlings: n = 16, y = 93.30 + 19.44x, r2 = 88%. Two-year-olds: n = 12; y = 89.85 + 18.05x

Maximal oxygen consumption (VO2max) is another parameter that can be measured with exercise testing. This factor has no correlation with maximum heart rate (HRmax), but there is one between the percentage of maximal heart rate and percentage VO2max, even VHRmax has a relation with VO2max (Evans and Rose, 1987). This is significant because when VO2 cannot be measured directly it can be calculated from these other readings.

The HR can be affected by multiple factors; these include age and breed of the horse, the state of the horse, training type (competition type), and the track or terrain the test is performed on. For the terrain, there is a difference in HR readings when taken on grass, sand, wood, or other track types, with sand having the lowest HR value. Yet interestingly enough the V200 was not significantly different in horses being ridden by lightweight riders and heavier riders (Couroucé-Malblanc and Erck-Westergren, 2016). Stress and excitement can also influence results as HR will be falsely higher in these states. This means for more accurate results the horse needs to be in a calm state.

Electrocardiography (ECG)

The ECG is commonly performed along with HR testing during exercise testing. This is used to examine the electrical activity of the heart, to diagnose arrhythmias which may occur after or during physical activity. One study has shown an association between cardiac arrhythmias and peak HR during exercise in racehorses (Ryan et al, 2005). This is why it is important to surpass the usual exercise intensity of the horse suspected with the condition. Disruption of cardiac rhythm which manifests during exercise can result in poor performance of the horse.

Blood Lactate

Lactate is a metabolic product found in the blood; it comes from anaerobic metabolism in the muscles. Its values can give information about the horse’s aerobic and anaerobic capacity. “At rest, blood lactate levels are 0.5–1 mmol/l. During exercise, a bilinear relationship occurs between blood lactate concentration and velocity” (Allen et al, 2016), yet, it is mostly shown as an exponential curve. The blood sample is taken from the jugular vein and transferred into tubes containing fluoride-oxalate or lithium heparin as anticoagulants. It can be either kept as a whole without centrifugation or test carried after centrifugation with the plasma. The whole blood is preferred over the plasma (although it lasts longer) as the lactate in the red blood cells is also measured this way, but the test needs to be done within 4 hours of sample collection. “The aerobic-anaerobic transition or onset of blood lactate accumulation (OBLA) has been defined empirically as 4 mmol/l blood lactate concentration” (Couroucé-Malblanc and Erck-Westergren, 2016).

Red blood cell volume and haematocrit

“Total red cell volume (RCV) is a major determinant of oxygen-carrying capacity.” (Couroucé-Malblanc and Erck-Westergren, 2016). Haematocrit can be measured following maximal exercise; consequently, it has been found by Couroucé-Malblanc and Erck-Westergren (2016), that the total RCV to bodyweight ratio is related to maximum trotting speed in Swedish trotters. Although the procedure used to measure RCV is not simple and cannot be done immediately, it is very useful to determine performance quality. However, in some breeds, this measurement is not a reliable test of quality performance ie. thoroughbreds.

Aerobic capacity

“Exercise-testing is used to measure aerobic capacity of the horse. Aerobic capacity is best assessed by calculation of maximal oxygen consumption (VO2max)” (Allen et al, 2016). One of the most frequently used tests is that of determining the VO2max, especially when assessing the performance of the human athlete, as "the competitive distance increases" (Allen et al, 2016). In the performance sector, VO2Max has become an increasingly important element of prediction, however other elements are also important to consider. Allen et al (2016) has stated “particularly running economy, which influences the percentage of VO2Max that can be sustained during prolonged exercise”.

In superior standardbred racing horses, a higher VO2max has been recorded compared to slower performing horses. An incremental exercise test is used to do the calculations for maximal oxygen consumption. "Oxygen consumption increases linearly with speed up until VO2Max. Which is defined as the point where no further increase of VO2Max is elicited despite further speed increases” (Allen et al, 2016). The measurement of oxygen can be measured on a treadmill with an open or biased flow system. Or a breath-by-breath system (Allen et al, 2016). Ventilatory data can be obtained by using the breath-by-breath system in combination with expired air alternatively open or biased systems can be used in a laboratory setting (Franklin et al, 2016) Exercise testing can be an important tool to accurately determine the oxygen consumption of the working horse and can help to predetermine upper respiratory tract problems in horses (Lane et al, 2006).

Physical

The increasing professionalism of equine sports disciplines is putting an increased load of training on sport horses. The many disciplines of equine sports have created varying requirements in energy and effort expended from horses (De Mare et al, 2017). Professional equine trainers use GPS heart rate monitors on the horse which constantly monitors their heart rate, as well as determining the inclination gradient of the surface that the horse is training on. De Mare et al (2017) explained the difference between sport discipline vs. performance requirement by saying that “at a given point a standardised exercise test can be used, however, an important issue is which type of SET applies best for which type of sports discipline." and further stated that "a standardbred used for trotting requires another type of performance capacity than a showjumper.".

“There are important differences in the exercise capacity between horse breeds” (De Mare et al, 2017). It is important to take into account that each discipline needs a specific set of abilities and stamina levels. In figure 4 we can see a showjumper horse being trotted by the rider to observe the horse's movements and in figure 5 we can see the rider training the horse.

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Figure 4 Horse being trotted without rider on the back.

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Figure 5 Rider jumping with the horse.

Thoroughbred horses

The performance of racing horses depends on their aerobic as well as their anaerobic capabilities, and interestingly, thoroughbred horses have been shown to reach a higher V200 value than other breeds (De Mare et al, 2017). It has been said by Plancke et al (2017) that "Incremental standard exercise tests are less suitable for thoroughbred horses because of the difficulty to make them run at constant speeds and to control track conditions". From this we can deduct that a single-bout test would be more suitable to assess the performance capabilities in Thoroughbred’s.

Eventing horses

Eventing horses are able to run up to 6270m at an average speed of 34 km/h, overcoming up to 40 obstacles within this time. During cross country, the heart rates of eventing horses have been recorded as 170-210 bpm and their blood lactate concentration at a maximum. The most common breed used for eventing is thoroughbred horses or thoroughbred- crossbreeds. Most commonly, a 3-4 incremental exercise test method is used (Plancke et al, 2017).

Dressage/Riding horses

Dressage has a minimum requirement of 4-8 minutes of demanding exercise at a time, thus the heart rate of the dressage horse reaches, but rarely exceeds, 150bpm. This suggests that the used energy supply during activity is partly aerobic during submaximal exercises (Plancke et al, 2017). Throughout a selected dressage movement, individual muscle groups contract intensively, thus the dressage horse needs strength as well as stamina to endure and carry out these movements precisely. Unfortunately, there are no specific tests as of yet to analyse the exact fitness levels of dressage horses (De Mare et al, 2017), however a submaximal exercise test at a low cantering speed can be recommended (Plancke et al, 2017). These tests can range from incremental exercise tests on track, as well as indoor riding tests and lunging tests. Fortunately, the lunging test does not need a galloping arena or an experienced rider, therefore it can easily be incorporated into the horses' daily exercise schedule (De Meeus et al, 2017).

Conclusion

Conclusively, it is evident that within the two different testing methods (field testing and treadmill testing) there are noticeably different benefits in using each test, which is dependent on and differs between specific sports disciplines. There has been great progress in this field over the last few years, however, there is still much to be learned and developed regarding equine exercise testing methods. We can also conclude that specific exercise testing is in fact necessary for the equine athlete, in order to obtain specified results which are needed for optimal performance.

References

Allen KJ, Erck-Westergren EV, Franklin SH (2016): Exercise Testing in the Equine Athlete. Equine Veterinary Education 28: (2) 89-98 13/03/2022

de Mare L, Boshuizen B, Plancke L, de Meeus C, de Bruijn M, Delesalle C (2017): Standardized exercise tests in horses: current situation and future perspectives. Vlaams Diergeneeskundig Tijdschrift 86 63-72 13/03/2002

Franklin SH, Van Erck-Westergren E, Bayly WM (2012): Respiratory responses to exercise in the horse. Equine veterinary journal 44: (6) 726-732 13/03/2022

Other references

Couroucé-Malblanc A, Erck-Westergren EV (2016): Exercise testing in the field. Veterian key. https://veteriankey.com/exercise-testing-in-the-field/#bib3 13/03/2022

Evans DL, Young LE (2016): Cardiac response to exercise and training. Vetinary key https://veteriankey.com/cardiac-responses-to-exercise-and-training/ 30/04/2022.

Kang, OD, Park YS (2017): Effect of age on heart rate, blood lactate concentration, packed cell volume and haemoglobin to exercise in Jeju crossbreed horses. journal of animal science and technology. BioMed Central. 15/03/2022 https://dx.doi.org/10.1186%2Fs40781-017-0126-8

Zuluaga Cabrera AM, Casas Soto MJ, Martínez Aranzales JR, Correa Valencia NM, Arias Gutiérrez MP (2021): Blood lactate concentration and heart rates of Colombian Paso horses during field exercise test. Veterinary and animal science https://doi.org/10.1016/j.vas.2021.100185 15/03/2022

Pictures taken by Celine Abela, Werner Bouwer.

Exercise_testing (last edited 2022-05-13 19:42:39 by 4601E)