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
session 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.
