TREADMILL EXERCISE TESTS

EXERCISE TESTING ON THE TREADMILL

David Evans PhD BVSc (University of Sydney)

Honorary Associate Professor, Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia

 

 

In this paper the focus will be on use of heart rate and blood lactate measurements during and/or after treadmill exercise. More technically challenging measurements such as oxygen uptake can be used, but that measurement will probably remain in the domain of university research laboratories for some time, given its cost and technically demanding nature. The presentation will focus on the heart rate and blood lactate measurements that can be easily performed, and which will provide a meaningful assessment of the state of training (fitness) of a horse in a commercial setting.

Measuring fitness:

1. Fitness for racing horses cannot be measured in horses standing quietly in their boxes

2. Fitness tests require measurements during exercise tests

3. Exercise tests can be conducted in treadmill laboratories, or on a racetrack

4. The main measurements for fitness assessment are heart rate, blood lactate and oxygen uptake

5. Heart rate measurements of fitness are the most suitable for field tests

6. Fitness tests should help an owner and trainer by providing information about differences in fitness between horses, and changes in fitness in individual horses. Ideally a fitness test should also help guide the racing and training strategies for individual horses.

7. Regular fitness tests (VHRmax) with heart rates in track gallops can assess performance, and evaluate poor performance. VHRmax can also help target appropriate training speeds to develop fitness in racehorses. Low values, or values that have decreased during training, indicate a need for a thorough veterinary examination for the possible causes.

The use of a treadmill for an exercise test can be complicated or simple. Simple methods are recommended, taking into account the rationale for the exercise test. What are the usual reasons for a treadmill exercise test?

1. To enable upper airway endoscopy during exercise

2. To measure the fitness of the horse

Fitness measurements are used to assess the responses to training and racing, and can help identify new clinical problems, and are used to assess horses with poor performance.

The protocols used for treadmill exercise testing vary greatly. It is not important that a protocol used in a university research setting is copied in a commercial setting. It is more important that a protocol is used that easily and quickly gives answers to the question being addressed.

Horses must be properly acclimated to the treadmill before conducting any measurements. This process should be patient, and only HR and lactate results in relaxed horses should be used for interpretation. Acclimation to trotting at 3.5-4.0 m/s (12-15 kph) and gallops at 6-8 m/s (20-26 kph) should be achieved over a 4-5 day period at least.

Unfortunately some horses enjoy treadmill exercise so much that their enthusiasm can make testing very difficult, as they push hard on the front restraint of the treadmill. Fortunately these cases are not common. As well, testing after a few days of rest should not be used, as horses are often excited, as they often are for racetrack exercise on Monday mornings.

There is no standard incline for testing. However, an incline of 10% (6 degrees) is often used. However, lower inclines can be used, and an incline of 2-3% has been suggested as most closely matching over-ground locomotion. However, it is not important to use a test that exactly equals over-ground locomotion, and it will never be fully achieved without jockey, saddle, bit in the mouth and so on. In any case, the recruitment of muscles during treadmill exercise is not exactly the same as in over-ground exercise. The treadmill does some of the work propelling the horse forward!

Most descriptions of treadmill exercise tests refer to standardised exercise tests that use a range of speeds. For example, a test could consist of trotting at 4 m/s for 5 minutes, followed by gallops for one minute at 6, 8 and 10 m/s. Heart rates could be measured during each step and during recovery. Heart rates during the test can then be used to calculate V140 or V200, the treadmill velocities at 140 or 200 beats per minute.

Ideally VHRmax should be measured in racehorse, but this necessitates measurement of maximum HR. Maximum HRs vary from 200-230 or more, and in trained racehorses treadmill speeds of 42 or more kph might be needed to record HRmax. An alternative is to record HRmax during a high speed track gallop.

A simple approach is to measure HRs during 5 minutes trotting, and record the lowest HR during that time. The lowest HR will most accurately represent the true HR because the effects of excitement are more likely to be eliminated. In racehorses, HRs might be from 90-140 bpm. HRs can also then be recorded during the last 10 seconds of one minute of gallop at 6 m/s. The result is HRs at trot and slow gallop HRs obtained in 6 minutes of exercise. Such a test would be appropriate for racehorses, eventers, jumpers, endurance horses, polo horses, and any horse that competes at a gallop. Dressage horses could probably be tested only at the trot.

Blood lactates could be collected via a jugular catheter during the exercise test, or collected 3-5 minutes after exercise by venipuncture, which is the author’s preference in a commercial setting. Blood lactate will not accumulate in trained horses until treadmill speed exceeds 8-9 m/s, depending on the fitness of the horse. In one study, commercially trained thoroughbred horses had blood lactates ranging from 3-12 mmol/l in blood samples collected after two minutes treadmill gallop at 10 m/s. The best horses had the lowest blood lactate concentration (Evans et al., 1993).

These approaches to treadmill testing enable monitoring of fitness during training, and simple comparisons can be made between horses. The author has found that superior racehorses have lower HRs during trotting and slow gallops, and higher VHRmax during track gallops. Superior racehorses also have lower blood lactates after standardised treadmill exercise test that finishes with a gallop at 10 m/s. These observations are supported by results in several research reports in thoroughbred and standardbred horses.

Regular monitoring of HRs during simple treadmill tests can answer simple questions. Is the horse getting fitter? Has there been a sudden increase in HRs (indicating a possible subclinical problem)? Has the horse properly recovered from its race, and so is then ready for more training? Simple treadmill tests assist with answering these questions.

Identification of horses with poor physiological capacity for exercise and with poor racing performance can assist with management of the training and racing of those horses. Perhaps the training can be modified to promote greater fitness, which can be measured. Perhaps the horse can be sold, so reducing costs associated with maintenance of horses with lower likelihood of earning prize money. However, it is important that the tests are repeated several times, to ensure that the data are reliable. If results are not consistent, repeat the tests.

Reference

Evans, D.L., Harris, R.C. and Snow, D.H. (1993) Correlation of racing performance with blood lactate and heart rate in Thoroughbred horses. Equine Veterinary Journal, 25:441-445

Tyler, CM, Golland, LC, Evans, DL, Hodgson, DR and Rose, RJ (1996) Changes in maximum oxygen uptake during prolonged training, overtraining and detraining in horses. J Appl Physiol., 81:2244-2249.