Regardless of whether your horse is used for high-level competition or weekend trail riding, it's important that he be fit for the task. "Fitness" is a rather vague expression, but in general terms it can be defined as the ability to complete the required amount of physical activity without fatigue, stress, or injury. A tired horse is more likely to take false steps or stumble, and thus is more prone to injuring tendons, ligaments, or joints. Therefore, even for the pleasure horse used for weekend trail rides, adequate fitness is important for his overall health and well-being.

So, how can you assess your horse's fitness during training? As a horse progresses through a conditioning program, it is often apparent that he is able to complete workouts with greater ease. Perhaps he sweats less during and after exercise, or appears less winded after completion of the workout--his respiration rate returns to resting levels more quickly than was the case before the start of training.

These observations are valuable, but not without limitations. To remove this "guesswork" and best gauge whether a training program is having the desired effect, some type of standardized fitness test is needed. In this article, we will discuss methods for assessing fitness.

Pros and Cons

There are several reasons why the regular assessment of fitness is a good idea. First, measurements taken during a period of conditioning provide a guide to the effectiveness of the training program. Or, if you have made a change to the training program, you can determine if there was a subsequent change in your horse's fitness. These same comparisons can be made year-to-year in an individual horse and related to actual performance in competitions. What were the results of fitness tests during a time when the horse was competing well or poorly? A decline in performance as revealed by exercise tests can be useful for the early detection of problems such as a subtle lameness. This might be seen as a slower overall time through a standard course, for example.

Perhaps the major drawback associated with fitness testing is the time and effort required. You need a suitable venue for exercise testing (more on this in a moment) and a reliable heart rate monitor (HRM) that permits the storage of heart rate (HR) data. Also, it is important to recognize that fitness testing is much more useful for monitoring the same horse over time than it is for comparing the fitness of two or more horses. Overall, however, the benefits of exercise testing far outweigh these drawbacks.

Exercise testing can be undertaken on a treadmill or in the field. Treadmill fitness testing has a number of advantages, including the ability to tightly standardize the exercise conditions (e.g., the speed and distance of exercise and the environmental conditions, particularly temperature and relative humidity) and to record a number of measurements that cannot be readily obtained under field conditions (e.g., oxygen consumption and blood lactate concentrations). Some training and rehabilitation centers have high-speed treadmills, making this type of testing feasible. However, for most of you, a field-based test is the most realistic option (more on this later).

Measuring Heart Rate

Heart rate is the key measurement during field fitness tests, so before describing the testing protocols, a brief refresher is needed on how to measure it.

At rest, the easiest and most reliable way to measure HR is to use a stethoscope (which can be purchased at most pharmacies). Place the stethoscope on the horse's left side behind the elbow, and note that each beat of the heart produces two distinct sounds--"lub-dub." You should count beats over a one-minute period. It is also possible to count heart beats without a stethoscope by placing your hand behind the horse's elbow on the left chest and feeling a "thud" each time the heart beats.

At rest, the HR of most horses is between 30 and 40 beats per minute. Obtaining a true resting HR, however, can be tricky. Sudden excitement, or even the act of placing a stethoscope on a horse's chest (something the horse might be unfamiliar with), can cause a dramatic increase in HR, perhaps to as high as 80-100 beats per minute. So, to obtain a true value for resting HR, the horse must be fully accustomed to the procedure. It is best to measure HR when the horse is standing quietly in his stall (and at a time when there is little activity in the barn).

During exercise, a heart rate monitor is needed to measure HR. These monitors record the electrical signals that initiate contraction of the heart muscle. For both humans and horses, the most widely used and reliable HRMs are those made by Polar, although models made by other manufacturers are also suitable. Polar now makes a HRM specifically for use in horses (the Polar Horse Tester). This system comprises a transmitter-electrode device and a wristwatch that displays the HR recordings. This is key--the rider receives constant feedback on the horse's HR response and can use this information to set exercise intensity during conditioning. These (and other) systems also allow the data to be downloaded to a desktop or laptop computer after exercise.

The two electrodes are positioned on the left side of the chest, above and below the position of the heart, and held in place by a fastened girth strap. The main problem with the use of HRMs is a loss of electrical contact between the skin and the electrodes. If you see unreasonably low, high, or erratic values, there probably is poor electrical contact.

During the winter, it is often necessary to clip the hair where the electrodes are placed. Also, make sure the girth strap fits snugly against the horse. Finally, you can buy special conducting gel to apply at the skin-electrode junction. Normally, however, the horse's sweat helps maintain good electrical contact.

Heart Rate and Fitness

At least in Thoroughbred racehorses, research studies have shown that there is an increase in heart size with conditioning--an increase in both muscle mass and the size of the left heart chamber. (The left ventricle is the chamber of the heart that pumps oxygenated blood throughout the body.) The "fit" heart is able to eject more blood with each beat (an increased stroke volume). Total cardiac output (and therefore oxygen delivery to the tissues) is a function of heart rate and stroke volume. The increased stroke volume allows cardiac output and oxygen delivery to the tissues to be maintained at a lower heart rate.

For this reason, increased fitness is generally thought to result in a slight decrease in resting HR (e.g., three to five beats per minute, or BPM, slower). In some very fit horses, resting HR might be lower than 30 BPM. However, because a horse's HR changes so dramatically with even mild excitement, resting HRs are not a reliable indicator of fitness status in the horse. On the other hand, the HR response during exercise and recovery is a good indicator of cardiovascular fitness.

With an increase in running speed (or exercise intensity when you factor in terrain and the deepness of footing), there is a straight line (linear) increase in HR up to values around 200 BPM. Thereafter, the HR response curve flattens as the horse approaches his maximum HR (HRmax). Beyond that point, there will be no further increase in HR despite further increases in running speed.

"Fit Horses' Heart Rates" on page 92 shows typical HR data at different exercise intensities. In Thoroughbreds and Standardbreds, peak HR is usually 220-240 BPM. Values for HRmax in other light breeds range from 200-215 BPM. Although HRmax does not change with increased fitness, the speed at which HRmax is attained will change with conditioning. To state this another way, as a horse becomes fitter, the HR at any running speed (except perhaps those which yield HRmax) will be lower compared to values recorded at the same speed before the start of conditioning.

With increasing fitness, there will also be a faster HR "recovery" during the one- to two-minute period after completion of exercise (i.e., a shorter period of time is needed for HR to return to resting levels).

Exercise Tests

In terms of exercise tests for assessing heart rate response and fitness, there are a couple of options. Both require use of a HRM with a built-in stopwatch. A simple test requires the horse to run a set distance at some target heart rate, usually around 180 BPM. The terrain should be level. After a thorough warm-up, running speed is increased until the target HR is reached. This work intensity is then maintained and the time taken to complete the set distance is recorded. With improved fitness, the average running speed at the target HR will increase.

The other approach calls for use of an incremental exercise test that more closely examines the relationship between HR and running speed. This test is best done on an oval track (three to four furlongs) that has a nice, even surface (grass, sand, or wood chip) and is without sharp turns. Again, a thorough warm-up (e.g., 15 minutes of walk, trot, and canter) should be undertaken before the test.

The basic idea is to perform four to five laps, with each lap run at a speed slightly faster than the previous one. The rider will use a stopwatch to record the start and finish of each lap (using the lap function on the stopwatch). A three- to four-minute rest interval can be taken between each lap, or interval.

The speeds chosen will depend on the type of horse (e.g., Thoroughbred racehorse or eventer vs. a pleasure/trail horse), but the general goal is to measure four to five speeds over a wide range of heart rates (e.g., 80-100 to 180-200 beats per minute). The most reliable HR values will be those recorded during the final 15 seconds of each lap.

For a Thoroughbred racehorse, a four-lap test might be run at 24, 21, 19, and 16 seconds per furlong. On the other hand, a reasonable fitness test for a Quarter Horse used for trail riding might comprise four two- to three-furlong laps at 55, 50, 45, and 40 seconds per furlong. An alternative approach is to run each lap at a target heart rate, e.g., 100, 125, 150, and 180 beats per minute.

Either way, repeat tests at regular intervals will allow you to assess cardiovascular fitness. As the horse increases in fitness, there will be a lower HR at any given speed or, when the test utilizes target HR values, an increase in fitness will be reflected in a higher speed for any given HR.

It is very important that the conditions for these exercise tests be standardized. The horse should be ridden by the same person, the same track should be used, and, as much as possible, the air temperature, relative humidity, and wind speed should be similar. The tests should also be run at the same time of day.

Interpreting the Data

Let's look at some actual data to see how HR monitoring can be used to track changes in fitness. The accompanying data are from a 10-year-old Thoroughbred gelding used for intermediate-level eventing. At the start of conditioning, the horse completed an incremental exercise test on a four-furlong grass track. After a warm-up, the horse completed laps at 14, 17, 20, and 23 mph (with five-minute rest periods between laps). HR was averaged during the last 15 seconds of each lap. The data are shown in "One Horse's Fitness Training Experience" above.

Similar tests were completed after four and eight weeks of conditioning. It is not possible to perfectly match the speeds used in the original test. However, this is not a problem because the aim is to look at the relationship between running speed and HR.

The next step is to plot the data, either by hand on graph paper or by using a spreadsheet program on a computer. The latter option is best because the computer program will draw the "line of best fit" through the data (linear regression). Otherwise, you must do this by hand. The data from the fitness tests have been plotted above.

An improvement in fitness is indicated by a rightward shift in the line representing the relationship between speed and heart rate. You can also calculate indices such as V200 (the running speed or velocity at a HR of 200 BPM) as shown. These indices are useful as a guide to changes in fitness.

The data from our Thoroughbred horse provide objective evidence (which is far more precise than noting how much he sweats or how heavily he breathes) that the conditioning program has improved his cardiovascular and aerobic fitness.

For now, heart rate monitoring during incremental exercise is the most practical means for assessment of fitness. Incorporating this type of testing into your horse's conditioning program will provide a useful guide regarding fitness and the effects of different conditioning strategies.

ONE HORSE'S FITNESS TRAINING EXPERIENCE


These speed and heart rate data are from a 10-year-old Thoroughbred event horse during an incremental fitness test before beginning a conditioning program.

Week 0

INTERVAL/ LAP SPEED (SECONDS/ FURLONG) SPEED (MPH) HEART RATE (BPM)
1 30 14 152
2 24 17 179
3 20.5 20 188
4 17.8 23 208


Following are speed and heart rate data from this horse during incremental fitness tests after four and eight weeks of conditioning.

Week 4 / Week 8

INTERVAL/ LAP
SPEED (MPH)
HEART RATE (BPM)
Week 4
Week 8
Week 4
Week 8
1
14.1
14.0
145
141
2
17.8
17.3
170
161
3
20.4
19.5
182
173
4
24.8
23.8
200
189


Below is the graph of the relationship between this horse’s speed and his heart rate during incremental exercise tests at weeks zero, four, and eight of a conditioning program.

Notice the increase in his running speed at any given heart rate at weeks four and eight when compared to his initial, unconditioned performance at week zero. This change indicates an improvement in his cardiovascular fitness as a result of the dedicated conditioning program.

10-year-old Thoroughbred eventer fitness graph

FIT HORSES' HEART RATES

SPEED OR GAIT

TYPICAL HEART RATE RANGE (BEATS PER MIN)
Rest
30-40
Walk
70-80
Trot
110-120
Canter (15 mph=2 furlongs/min)
160-170
Canter (22 mph=3 furlongs/min)
195-200
Gallop (28 mph=4 furlongs/min)
210-220
Recovery--one minute (walking)
100-110
Recovery--two minutes (walking)
80-85

About the Author

Ray Geor, BVSc, PhD, Dipl. ACVIM

Ray Geor, BVSc, PhD, Dipl. ACVIM, is professor and chairperson of Large Animal Clinical Sciences at the College of Veterinary Medicine at Michigan State University

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