Page 100 - May 2022

VETERINARY VIEWS
By the time a rider dismounts and starts to take a horse’s pulse, it will have dropped by half, or be at least 20-50 beats per minute (bpm) below the working heart rate.
effort may indicate beginning fatigue. Rather than ignoring the hard, cold data displayed on the heart rate monitor, check for a reason and slow his pace. Pushing on as before could lead to metabolic or musculoskeletal problems.
As a training tool, a heart rate monitor evaluates a horse’s current level of fitness.
A horse conditioned for a particular work effort performs that task at progressively lower heart rates as fitness improves. For example, an unconditioned horse may exercise at 120-150 bpm, whereas a fit horse covering the same terrain may work between 80-110 bpm. Tracking a horse’s progressive improvements then allows a push to greater work intensity, such as fartlek (aka “speed play” - periods of fast work mixed with periods of slower work) or interval training. Increase each stress in small increments to allow a horse’s cardiovascular and structural systems to respond and adapt with less risk of musculoskeletal injury.
A horse’s heart works harder if carrying a heavier load. Preferably, the combined weight of rider and tack adds up to less than 20% of a horse’s body weight. Adding a heavier saddle or more equipment as a training tool increases a horse’s effort. The heart rate monitor enables experimentation to figure out how much “stuff” to use to achieve a training effect.
Some horses work at a higher heart
rate than others. This does not necessarily mean such a horse is less fit; only that at
a certain working heart rate that horse
finds a comfort zone in which his muscles efficiently propel him through the exercise. Each horse should be compared to itself, and not to others. There is a danger in using a heart rate monitor like a tachometer.
However, the lower the working heart rate, the less oxygen a horse must consume to fuel his muscles, and the less effort he expends. The lower the working heart rate, the easier it is for a horse to quickly reach recovery criteria. The rate of the heart rate drop is most critical and is what actually indicates fitness for an exertion.
MONITORING HEART RATE RECOVERY
Ideally, a horse’s heart rate recovers to
less than 60-64 bpm within 5-10 minutes following an aerobic workout. If the heart rate remains high, consider possibilities for the delayed recovery: a) too much exercise stress for the horse’s current level of conditioning means the pace and/or intensity of the work should be ratcheted back; b) musculoskeletal pain; or c) impending metabolic problems created by fatigue or dehydration.
Horses in aerobic exercise should recover
to a HR less than 64 bpm if the horse is well- conditioned and strategically ridden. If the HR hovers above 64 bpm more than 15 minutes after a rest, he is probably being pushed too hard. After a conditioning workout, if the horse recovers to a heart rate of less than 52 bpm within 10 minutes, he likely isn’t “stressed” enough to achieve an adequate training effect.
USING THE HEART RATE MONITOR FOR CARDIAC RECOVERY INDEX (CRI) Another means of evaluating a horse’s ability to recover in the face of exercise stress (espe- cially aerobic work) is the use of the Cardiac Recovery Index. Once a horse is stopped after a work and has recovered to a heart rate between 60-64 bpm, take a “resting” heart rate. Then start a timer as the horse
is trotted 250 feet. At exactly one minute, re-count the heart rate to see the recovery value. Periodic checks during a training period gives a handle on how well a horse is responding to the day’s workout.
A CRI increase of 4 bpm above the horse’s base rate before the trot out indicates he is not recovering to a preferred level, so lighten up the training effort. An 8-bpm increase over base indicates a lack of recovery. Repeat a questionable CRI after
a 10-15-minute rest period. If it remains increased, start looking for reasons. Either your horse is experiencing metabolic difficulties, or some structural body part is causing pain, either from musculoskeletal injury or saddle sores.
FITNESS TESTS
Fitness tests help measure a horse’s aerobic capacity during training. Each of several methods requires use of a heart rate monitor.
One method is to bring the horse to a working heart rate of 160 bpm and measure the time it takes to cover a set distance (for example, a mile) while keeping his heart rate working at 160 bpm. This measures a horse’s velocity at a heart rate of 160 bpm, also called the V160. A heart rate of 160 bpm is used
to carry out these tests because that heart
rate touches the anaerobic threshold in most horses. As fitness improves, the horse travels faster at this heart rate over that distance.
Another technique asks the horse to cover a distance of 1-3 miles at a constant speed such as a working or extended trot
or slow canter. Measure the time it takes to cover this distance at a constant heart rate. After a rest, repeat the exercise again but at a faster speed. Repeat this once or twice more. Plot the horse’s speeds and heart rates on a graph to give an estimate of the V160.
Well-conditioned horses in aerobic exercise should recover to a heart rate of less than 64 bpm.
To use the Cardiac Recovery Index (CRI), take a resting heart rate and then start a timer as the horse is trotted 250 feet. After exactly one minute, re-count the heart rate to see the recovery value.
98 SPEEDHORSE May 2022
Getty Images Getty Images Myriam Maynard, Speedhorse