The difference between finishing and failing to finish generally can be summed up in one word--fitness.
All competing horses should be fit, but the endurance horse requires a conditioning program that takes a definitive step beyond most others.
The difference between a horse being in condition for a western pleasure class at a horse show and being fit enough to run an endurance race is about as profound as that between someone who is in shape to play recreational golf and a runner who is about to compete in a marathon.
Every aspect of a horse's skeletal, muscular, and cardiovascular systems must be functioning at the optimum if it is to be a successful endurance race competitor. Developing a fit endurance horse requires dedication, energy, and knowledge.
The rider must first understand what happens within the horse's system as a conditioning program develops, then must apply a training regimen that will achieve a positive end result.
First, a quick glance at the equine's cardiovascular system.
Cardiovascular Fitness
An adult horse weighing in at about 1,000 pounds contains more than 13 gallons of blood that is circulating through its body. This moving blood has a couple of prime jobs to perform. First, it must deliver oxygen from the lungs to the individual tissues of the body. Second, it must deliver nutrients, absorbed from the digestive tract, to the tissues. The cardiovascular system also carries waste products of cellular metabolism to the lungs and kidneys for removal from the body.
A horse's blood flow is mainly determined by metabolic activity of the tissues. The greater the metabolic activity, the greater the blood flow. When a horse is at rest, there is little metabolic demand and, as a result, its heart rate may be as low as 25 beats per minute.
However, when great metabolic demands are made on the equine system, such as a sustained burst of speed, the heart rate might zoom as high as 250 beats per minute. At 250 beats per minute, the cardiac output is at the rate of approximately 55 gallons of blood being pumped by the heart each minute.
As a horse becomes more fit, stroke volume (the amount of blood pumped with each beat of the heart) tends to increase and heart rate at a particular speed decreases.
The reason the heart rate increases with movement is that when a horse makes the transition from rest to exercise, heavy demands are made on limb muscles to increase locomotion. This increased metabolic activity leads to increased blood flow demand. To accommodate this demand, the heart rate quickens and the blood flow is increased.
A key factor in endurance horses is recovery rate. This means that when a horse comes into a veterinary checkpoint during an endurance race, its heart beat must return to relatively near its personal norm while at rest before it is allowed to continue.
In the fit endurance horse, the recovery time will involve only a matter of minutes. The fit endurance horse, after reaching a rest-checkpoint area, will take a few deep breaths while walking about and its heart rate will immediately and rapidly become lower. In about 10 minutes, it should have reached an acceptable level for continued competition.
Blood flow serves another valuable function in the endurance horse. It aids in the cooling process by diverting blood toward the skin surface when heat builds up within the animal's body core.
Muscle Structure
Muscles are comprised of a variety of fibers, each of which has distinct functional and metabolic characteristics. Craig H. Wood, PhD, of the University of Kentucky, described muscle fibers like this: "Muscle fibers can be classified in two broad classifications. Type I fibers are slow-contracting fibers, have low ability to oxidize glucose or glycogen rapidly (glycolytic activity), are fatigue resistant, and utilize fuels in the presence of oxygen (aerobically). These fibers are used for long-term, non-strenuous work. They also provide endurance.
"Type II fibers are fast-contracting fibers that fatigue much more quickly and have high glycolytic activity. Type II fibers can be further classified as type IIA, IIB, and IIC, according to the myosin structure.
"Type IIA fibers are used for speed at longer distances, whereas type IIB fibers are used for quick bursts of speed over a short distance. Type IIA fibers can utilize fuels aerobically, while type IIB fibers have low aerobic capacity and tend to depend on anaerobic (without oxygen) pathways for energy production. Type IIC fibers are transitional fibers, which can be recruited to be IIA or IIB depending on the training program and are generally found in young horses."
Wood also offers some succinct observations concerning muscle structure and tone as related to fitness training: "Muscle is an extremely adaptable tissue and the adaptations are related to the specific type of training the muscle tissue gets. Training results in an increase in capillaries that can deliver oxygen to muscle and an increase in the number of mitochondria in the muscle cell so that more oxygen can be utilized per unit of muscle. These changes are brought about by modifying training intensity and duration.
"Endurance training will enhance the aerobic system, thus allowing the muscle to use fuels through oxidation. Training for quick bursts of high intensity exercise involves training for strength. Increasing strength involves increasing muscle mass by increasing the number of sarcomeres (a sarcomere is the basic contractile unit of skeletal muscle) parallel to existing sarcomeres. High intensity work for short periods of time will increase strength.
"Training will improve functional metabolic capability of the muscle fibers involved and may very well change the proportion of muscle fiber types in a given muscle. Muscle adapts much more rapidly to training programs than other tissues in the horse's body and will subsequently lose the effects of training more rapidly."
One of the end products from burning muscle fuel when a horse is traveling at high speed is lactic acid, which causes a fall in muscle pH and often results in fatigue. However, the endurance horse normally will travel at speeds that can be maintained almost entirely through aerobic energy generation, which results in far less lactic acid production. Only during hill climbing and for bursts of speed are the endurance horse's energy demands too great for aerobic regeneration.
Fatigue in endurance horses is more apt to be a result of glycogen depletion than from lactic acid accumulation.
The Respiratory System
A working horse needs oxygen. Without oxygen, muscles have difficulty functioning. In order for the working horse to perform at its peak, it might have to take in air at a rate that is high enough to supply the body with as much as 90 liters of oxygen per minute.
It becomes instantly obvious that an endurance horse must have a superior respiratory system in order to continually supply its body with the amount of oxygen needed over the course of a 50- or 100-mile race.
Horses with a partial paralysis of the muscles in the larynx that can reduce the size of the windpipe are poor candidates as endurance race competitors. Even a small reduction in the size of the windpipe can greatly reduce the amount of air that can reach the lungs.
Horses with chronic obstructive pulmonary disease or "heaves" are also poor endurance race candidates, as are horses with exercise-induced pulmonary hemorrhage (EIPH).
Thermal Regulation
The horse generates a significant amount of metabolic heat during exercise, and this must be dissipated to prevent thermal injury. Research carried out at The Ohio State University Equine Exercise Laboratory and elsewhere has shown that even short-term submaximal exercise on a treadmill can result in an elevation of body temperature to 103 degrees Fahrenheit. Without proper cooling, body temperature during endurance rides can reach up to 106 degrees Fahrenheit, resulting in heat stroke or other thermal injuries.
A horse's prime weapon in dissipating heat is through the evaporation of sweat. However, when the weather is hot and humid, there is little evaporation and sweating might fail to dissipate enough of the accumulated heat.
Kenneth H. McKeever, PhD, FACSM, a researcher at Ohio State, describes what happens within the horse's thermo-regulatory system when it becomes overheated: "As heat accumulates, blood flow is increased to the skin to enhance the transport of heat from deep in the core of the body to the surface. As exercise progresses, however, heat loss leads to progressive dehydration and loss of plasma water from the bloodstream.
"This phenomenon results in a decrease in circulating blood volume and cardiac stroke volume. To maintain cardiac output, the horse must increase its heart rate. This phenomenon is referred to as 'cardiovascular drift.' When dehydration cannot be compensated for by cardiovascular adjustments, body temperature rises and is soon followed by a decrease in performance and fatigue."
Thus, even the most fit endurance horse will suffer from dehydration if it does not receive enough water during a race or training session. One researcher estimated that under certain heat and humidity conditions, a horse's sweat loss can exceed 12 liters per hour.
Sweat loss can cause another imbalance that can be highly detrimental to the endurance horse--depletion of electrolytes, such as sodium, potassium, and chloride.
Equine sweat is hypertonic, which means it contains a significant amount of salts. Under normal conditions, a horse's electrolyte balance can be maintained via a balanced ration and access to a salt-mineral block. Not so with the training and competing endurance horse, especially in warm weather. The horse might require a supplementation of electrolytes on a regular basis.
The Fit Horse-- One Competitor's Opinion
Now that we have taken a brief look at how the key systems of the endurance horse function, how do we weld them all together with a fitness program so that every aspect of the horse's system is functioning at its optimum?
Steve Hanson, an endurance racer who has competed with great success in both 50-mile and 100-mile races, and who now lives in Billings, Mont., has provided his recommended training regimen for getting a horse fit and ready for its first 50-mile competition.
He begins with the assumption that the objective is to enter and complete--not win--a 50-mile endurance race within six to eight weeks after commencement of a conditioning program.
"During the entire conditioning phase prior to the first competition, we will be working the horse four to six days per week, and during this first week, we are going to spend a couple of days just walking him," said Hanson. "Walking the prospect four to five miles each day for the first two or three rides will allow us to precondition the horse's back to the saddle tree, work through some initial muscle soreness at a slow pace, and permit horse and rider to get accustomed to each other.
"Prior to or during this first part of the conditioning process, we should closely monitor the horse's pulse and respiration. Most successful distance horses have a preconditioning pulse of less than 40 beats per minute and take no more than 12 breaths per minute. While respiration readings can be taken easily by viewing the horse's underline anterior to the flank/stifle area, it is best to obtain a stethoscope to monitor the horse's heartbeat.
"Also, at the beginning of the conditioning program, thoroughly palpate the horse all over its body, to determine if there are areas of heat or tenderness. Throughout the conditioning program, the legs should be palpated before and after each workout.
"After the second or third day of riding at a walk, we should gradually increase the pace of our workouts so that by the end of the first week, we are riding four to eight miles each day, alternately walking and slow trotting.
"As we move into the second week of training, we will mix in a medium trot, increasing the pace of our workouts but not the distance.
"By the third week, we should be doing some fast trotting and slow cantering, always alternating the pace frequently during the ride, as well as working in some moderate hill work.
"By the fourth week, our horse should be ready for more intensive hill climbing. At this point, we will be doing very little walking, other than to allow the horse to recover from a strenuous hill climb.
"Training runs should be at least five to eight miles each day, with a schedule which allows the horse one to two days of complete rest each week. Working the horse more than 12 miles during a workout on an occasional basis is fine, but to do that consistently is asking for trouble with a green horse. Even a seasoned campaigner can rarely stand up to that regimen.
"As the intensity and distance of workouts has increased, the horse's cardiovascular system should have been improving on a parallel course until we reach the point, usually during the fourth or fifth week of training, where we can trot or canter the workout course, and within 10 minutes of recovery time take a pulse reading of 68 or less. Respiration levels, except in cases of extremely high humidity, should be eight to 16 breaths per minute within the same time period.
"In the final week or two of preparation prior to the first competition, we are not going to work the horse extremely hard. Remember, first, that the goal is to finish this ride with the horse in a sound condition and ready to go on to the next ride, with little or no consideration for order of placing.
"Second, while the horse will certainly maintain condition achieved up to a point in time occurring one or two weeks prior to the ride, its fitness level is probably not going to be enhanced significantly by more arduous workouts during that last week or two.
"Third, we want our equine partner to come into the race feeling fresh, bursting with vitality, and if we have conditioned right up to the day of the race, he is going to have less energy and will be in the process of recovering from his last workout rather than stepping out smartly with unreleased energy.
"So, during this last week or two we will ride him lightly but frequently; enough to take the edge off every day or every other day, at shorter distances than those to which he has become accustomed, but not enough to deplete all of his energy reserves.
"The two days prior to the race, we will not ride him at all except for perhaps a short three or four-mile jog on the race trail itself after we get to race headquarters."
That, then, is a suggested blueprint from one expert in the field for starting a green horse and getting the animal fit. Other successful racers might use other regimens.
There is also the matter of horse selection. Not every horse is designed--structurally or emotionally--to be an endurance horse, but that is a whole new subject. The key factor to success, once the proper mount has been selected, is, and always will be, fitness.
Xeno Muller, Olympic gold and silver medalist, indoor rowing, rowing technique.
