PREPARATION AND CONDITING

2006/11/03 06:29 / Horse Racing/Theory

PREPARATION AND CONDITIONING

by William E. Day, PhD
Logan, Utah
AAHS Vice President,
Equine Education

[reproduced from Spring 2002 Caution:Horses]

Equine (as well as human) physiology naturally but gradually compensates and strengthens (shaping up) during times when more work is needed.  But like us, horses can quickly lose conditioning or “get out of shape” during long periods of rest.  That is, a strenuous mountain ride would not be an appropriate activity just after 3 months of pasture or stall rest.  In this article we will briefly go over some of the factors you should consider as you prepare your horse for upcoming events and activities.  These factors include: cardiovascular fitness, respiratory fitness, thermoregulation, muscle fatigue and skeletal fatigue.

Cardiovascular fitness- The resting heart rate of horses is approximately 35 bpm and can reach up to 250 bpm during extremely high intensity exercise.  Each beat can pump between .8 and 1.2 liters of blood.   Therefore, a horse exercising at maximum intensity can pump enough blood to fill a 55 gal drum in 1 minute!  As a horse becomes more fit, the stroke volume increases permitting sufficient oxygen transport with fewer beats.  Conditioning exercise will improve blood circulation through muscles.  As blood circulates more efficiently through muscle, more oxygen is made available, and more heat can be removed.

Respiratory fitness- Respiration is of course how oxygen is introduced to the horse’s blood.  Limiting factors can influence the amount of available oxygen.  These include, the volume of the lungs, the diameter of the airway from the nostrils through the windpipe, and their gait (since horses breathe in rhythm to their stride). One reason horses breathe faster during hard work is directly related to the pH of the blood.  The more acidic the blood (from CO2 and Lactic Acid) the harder the horse will breathe to get rid of excess carbon dioxide as well as to take in sufficient amounts of oxygen.

Thermoregulation (dissipation of heat)- Working muscles produce heat.  Horses have two ways to remove it.  One is through breathing heavily.  Horse’s lungs are very large and the expiration of hot air and inspiration of cool air helps to reduce the temperature of the body, especially the area around the heart.

The second is, of course, through sweating.  As a horse overheats, blood vessels in the skin become dilated so that they can hold more blood.  Then evaporation/transpiration of sweat helps to cool the horse much like a swamp cooler can cool a house.  The sweating mechanism works best in cool, dry air.  Warm and/or humid conditions may cause many horses to have more difficulty in keeping cool.

Fat horses and horses with heavy muscling are not able to eliminate heat as efficiently as leaner and lighter muscled animals.  Safety becomes a concern when overheated horses become lethargic and uncoordinated.  Conditioning exercise (particularly walking and trotting) in balance with proper feeding will remove body fat and improve your horse’s ability to dissipate heat. Also, as blood circulation through muscles improves, their heat can be more efficiently carried to the skin for cooling.

Muscle Fatigue ? Working muscles need fuel.  During normal (aerobic) exercise (walking or trotting on level ground), fuel stored in muscles is combined with oxygen from the blood to produce energy and motion.

During intense exercise (exercise that causes the heart rate to exceed 150 bpm), oxygen is depleted more quickly than it can be supplied.  Many of the cells in the muscles then switch to an energy system that does not require oxygen. The main problem with this anaerobic system is that it requires over 10x the amount of fuel to produce the same amount of energy. This system also produces lactic acid as metabolic waste.  If too much lactic acid accumulates in one area of the muscle, inflammation and soreness result.  With a proper conditioning regimen, your horse will gradually improve his ability to both take up oxygen and deliver oxygen to working muscles.  Conditioning will also improve his ability to rid muscle tissue of metabolic wastes before they can build up and cause any damage.

One good way to help insure that your horse’s muscles remain healthy after a high intensity work effort is to allow 30 minutes or so of walking and light work to allow the horse to “cool out” before going back into a trailer or stall.  During this cool out period, lightly active muscles allow blood and lymph fluids to circulate and rid muscular tissues of metabolic waste and heat much better than if the muscles were not moving.

Skeletal Fatigue-  The skeletal system includes your horse’s bones, joints, tendons and ligaments.  If overstressed, skeletal failure can cause abrupt and serious injury to both the horse and rider.  Overworked horses are more likely to suffer sprains and strains when at a crucial moment in the horse’s stride a particular muscle fails to contract, resulting in a momentary and sometimes repeated mal-positioning of a related joint or ligaments.

During exercise, your horse’s bones, joints and ligaments are constantly changing to adapt and compensate for activity changes and to the rider’s added weight.  How they compensate is specific to the type of work performed.  For example, roping, cutting or barrel racing horses will not necessarily be prepared for a strenuous day of climbing steep grades on a long mountain ride.

One big problem with skeletal conditioning is that compensatory changes occur much slower than circulatory, respiratory and muscular conditioning.  It takes approximately 60 days of 5d/week riding for the density of a horse’s cannon bones to adapt to more strenuous activity and to carrying the added weight of a rider.  Therefore, while our horses may feel fit, the vast majority of us (weekend riders) do not ride enough to cause any significant changes in skeletal fitness.  Unconditioned bones, joints and ligaments are especially susceptible to shock, twists and torsion.  For this reason, riders should always be careful to slow horses to a walk on surfaces that are hard, slippery, uneven or deep.

To sum up, before you expect your horse to perform a new type of activity, consider how well his varied systems have been prepared.  To avoid problems, always introduce high intensity work gradually, allow plenty of time after a high intensity work effort for the horse to “cool out” before returning to a stall, and keep in mind that physical limits vary with weather conditions or between horses and that fatigue may set in sooner than you expect.  Good luck and safe trails.

10 steps to lameness on the trail for an “out of shape” horse (hypothetical):1st Work intensity exceeds oxygen supply to working muscles >>>
2nd Aerobic function is limited >>>
3rd Anaerobic function is increased >>>
4th Rider fails to recognize symptoms of anaerobic onset >>>
5th Lactic acid production increases >>>
6th Circulation is inadequate to remove lactic acid >>>
7th Fuel in individual muscles is depleted>>>
8th Fatigue and soreness cause changes in movement >>>
9th Changes in movement cause forces to be distributed differently on supportive ligaments, joints and bones >>>
10th A bad step causes a fall and/or injury.

How to tell that your horse is approaching his limitations:1. Panting or blowing respirations
2. Heart rate more than 150 bpm
3. Profuse sweating

If these symptoms occur:1st Stop and rest
2nd If your horse is still breathing heavily and/or the heart rate has not gone below 100 bpm after 5 minutes of rest, discontinue his exposure to intense work for a few days.  For instance, if trail riding, it would be best to dismount and walk until the horse is rested, then chose less strenuous routes on subsequent rides until his conditioning improves.
3rd If your horse continues to blow and sweat after several minutes of rest, you may have overworked your horse.  Immediately discontinue riding, cool him out and consider him off limits for at least a week.

2006/11/03 06:29 2006/11/03 06:29
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Horses for courses

2006/11/03 06:18 / Horse Racing/Theory

British Journal of Sports Medicine 2005;39:581
ⓒ 2005 by BMJ Publishing Group Ltd & British Association of Sport and Exercise Medicine

EDITORIAL

Warm up

Horses for courses

Paul McCrory

Some of you may have read the paper in the Journal from a few years ago discussing the human athletes in professional horse racing and the risks they face in the course of their occupation.1

But the jockey is not the only athlete in this sport and for some folks the horse is a far more important determinant of pecuniary return. There are may parallels in equine sports medicine that make interesting reading for the human sports clinician. Horses it turns out get stress fractures, cruciate ligament injuries, as well as a whole raft of other musculoskeletal pathology. They even have their own alternative practitioners in addition to the sports veterinarians.

One critical area where equine science far outstrips human sports medicine is genetics. In part, this reflects the historical culture of the sport where selective breeding in racehorses has long been developed.

It turns out that more than one-third of the entire gene pool of the current thoroughbred horse population in the United Kingdom derives from just four horses imported from the Middle East and North Africa in the 17th Century. Further, approximately 50% of the gene pool is provided from 10 horses whilst 80% is made up from only 31 horses.2

It is not just thoroughbreds where this is seen. In the US, 13 of the top 15 quarter horses are descendants of a single horse called "Impressive". This horse had a particular genetic abnormality that was passed on to his offspring, which was a sodium channel mutation that enabled far greater and quicker power to be generated by muscle contraction. While improving his horsepower it also placed horses with this mutation at risk of a form of paralysis that can be fatal.2,3

One criticism that arises from such figures is the concern as to whether this type of breeding significantly reduces the gene pool of race horses thereby restricting their ability to evolve over generation into ever more faster beasts. Certainly thoroughbred horses have low fertility rates when compared with wild horses; however, only minimal inbreeding has occurred (at least over the past five generations) and the reduced fertility may have alternative causes.4 Despite this, an analysis of winning times from the English St Ledger, Oaks, and Derby races from 1840 to 1980 demonstrated improvements of approximately 0.6% per generation, which suggests that horses will continue to improve their racing performance.3

Another answer to this question is given by data from Ireland tracking horse racing performance from 1961 to 1985. This study analysed 31 263 3 year old racehorses to see whether the performance of related horses was different to randomly selected non-related horses. The results suggested that only 35% of the variance in racing performance could be explained by genetic factors with the remainder being attributed to nutrition, training, riding skill, and other environmental factors.4

It may be stating the blindingly obvious but horses do have some physiological differences to elite human athletes. One anatomical constraint is the fact that because of the attachment of the horse’s foreleg muscles to its ribcage, when the horse is galloping, the ground impact creates a bellows effect where the ribs are forced upwards and the abdominal contents move forward forcing the air out of the lungs. Thus the horse can only take one breath per stride, which in turn creates an upper limit to physiological oxygen delivery. If the horse tries to increase its stride length without changing the stride frequency, it does not have the ability to commensurately increase its breathing frequency.5?7

As a consequence of this process, many horses have blood in their windpipe after a race with the vast majority having blood in their lungs. This blood may further interfere with oxygen transfer to the blood and hence effect oxygen delivery to the muscles.6,7

Because of this physiological limitation, unscrupulous individuals may attempt to modify oxygen delivery and transfer by pharmacolological means. Once again, veterinarians are at the forefront of drug detection and testing in order to keep the sport honest.

We could do a whole lot more I believe by rediscovering comparative anatomy as part of our sports medicine training. Two hundred and fifty years ago, the celebrated John Hunter became the father of modern scientific surgery by following this route. Those visiting or living in London should take the time to pay a visit to the newly re-opened Hunterian Museum at the Royal College of Surgeons in Lincoln Inn Fields and discover where much of our current anatomical and surgical knowledge derives. Those of you who are not in London should read his newly published biography, The Knife Man, to gain an insight into his work.8

With all the recent fuss about identity cards, perhaps there is an undiscovered benefit that could be utilised namely tracking gene cheats in sport. We can take another leaf out of our veterinary colleague’s book here.

It may be of interest to folks to know that since 1791, when James Weatherby established ‘The Stud Book’, the intricate details of genetic breeding has been meticulously documented for more than 20 equine generations in the UK making this record the quintessential guide for horse breeders.2,3 Can you imagine a world designed to stamp out gene cheats with the combination of a biometric sporting passport with a DNA sample as well as physiological data coupled with an elite athlete stud book to monitor breeding. Do I hear some antediluvian cries of eugenics?


REFERENCES

  1. Turner M, McCrory P, Halley W. Injuries in professional horse racing in Great Britain and the Republic of Ireland during 1992?2000. Br J Sports Med 2002;36:403?9.[Abstract/Free Full Text]
  2. Cunningham P. The genetics of thoroughbred horses. Scientific American 1991;264 (5) :92?8.
  3. Budiansky S. Don’t bet on faster horses. New Scientist 1996; (10 August) :29?31.
  4. Gaffney B, Cunningham E. Estimation of the genetic trend in racing performance of thoroughbred horses. Hum Genetics 1988;103:48?50.[CrossRef]
  5. Derman K, Noakes T. Comparitive aspects of exercise physiology. In: Hodgson D, Rose R, eds. The athletic horse: prinicples and practice of equine sports medicine. Philadelphia: WB Saunders and Co, 1994.
  6. Rose R, Hodgson D, Kelso T, et al. Maximum O2 uptake, O2 debt and deficit and muscle metabolites in thoroughbred horses. J Appl Physiol 1988;64:781?8.[Abstract/Free Full Text]
  7. Evans D, Harris R, Snow D. Correlation of racing performance with blood lactate and heart rate after exercise in thoroughbred horses. Equine Veterinary Journal 1993;25:441?5.[Medline]
2006/11/03 06:18 2006/11/03 06:18
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Kentucky Derby: Race Horse Physiology Is Model For Speed

2006/11/03 05:39 / Horse Racing/Theory

EMBARGOED FOR PUBLICATION UNTIL MAY 2

APS ContactChristine Guilfoy
(301) 634-7253
cguilfoy@the-aps.org

Kentucky Derby: Race Horse Physiology Is Model For Speed

Equine athlete has natural supplemental oxygen supply ready for race; blood thickens 50% with infusion of oxygenated red blood cells

BETHESDA, MD (April 27, 2006) ? When the elite horses of the Kentucky Derby jump from the gate on May 6, will the physiologists who study them be able to predict the likely winner?

Exercise physiologists have used horses for research for hundreds of years because the equine athlete’s blood vessels are large, they love to exercise, and they are domesticated, noted Eric K. Birks, assistant professor of exercise physiology at the University of Pennsylvania School of Veterinary Medicine.

Important discoveries about heart rate, blood clotting, blood pressure and the role of oxygen in the blood have resulted from research with horses, said Kenneth H. McKeever, associate professor and associate director of the Equine Science Center at Rutgers University, New Brunswick, NJ, and an advisor to the New York state racing board’s medication advisory committee.

And the research continues. McKeever, for instance, is currently doing research funded by the U.S. Army, looking at the anti-inflammatory properties of several foods. Soldiers, who run and walk with lots of heavy equipment, often develop inflammation, which can lead to injuries, he said. His team found that extracts of cranberry, black tea and orange peel reduced inflammation in horses, but ginger did not. This finding could help soldiers reduce inflammation by eating these foods.

Born to run

Physiologists use treadmills to identify how the horse’s physiology contributes to maximum performance and how it limits it. Getting a 1,200 pound thoroughbred to run on a treadmill has its challenges, but part of the reason the horse has become a favorite of exercise physiologists is that they love to run, McKeever said.

“That’s part of the lure of using horses rather than rats or monkeys -- they give it their all,” said McKeever. Horses in his lab paw at the belt when they get on the treadmill, trying to get it to move, he said.

“If they had opposable thumbs, they would open their stalls and go down to the treadmill themselves,” said Birks. “Left to their own devices, the horses would probably run more than what we allow them to run in races.”

And what have physiologists learned about horse physiology?

Fun physiological facts about horses

Horses

  • can breathe only through their noses

  • can only breathe in synch with their stride

  • have outsized spleens that release oxygen-rich red blood cells into the blood stream when they run

  • have hearts that can handle blood that thickens with the 50% increase in red blood cells

  • are the only animals, other than humans, that sweat through their skin

A horse’s body is like a huge bellows, McKeever explained. Its breathing is dictated by the movement of its body and is in synchrony with its stride. Horses can inhale only when their front hooves are striding outward, they exhale only when all four legs come together -- the in and out of the bellows.

Unlike human runners who can take a deep breath independent of their leg movements, horses cannot take that extra-deep gulp of air when in full gallop, said Lawrence R. Soma, professor of anesthesia and clinical pharmacology at the University of Pennsylvania School of Veterinary Medicine. That means a horse with a longer stride has more time to inhale and exhale, allowing the horse time to breathe more deeply. Horses cannot increase their breathing rate without running faster or shortening their strides.

"Because they have such a big mass of abdominal contents, if they tried to inhale when landing on their front feet, this mass and any food in their stomach and intestines would shift forward and limit the expansion of their lungs," Birks explained.

The horse with the longer stride has an advantage, because it has more breathing time, Birks said. Triple Crown winner Secretariat had one of longest stride ever recorded, allowing him to take bigger breaths, he said. So, the longer the stride, the more likely to win, right?

Thoroughbreds share same 30 ancestors

Unfortunately, it’s not so simple. Some very successful horses have had shorter strides, including Kentucky Derby and Preakness winner Smarty Jones. Racing success is built on multiple factors, including the horse’s psychological makeup, not to mention the jockey’s, Soma said.

The horses that run the Derby run approximately the same speed, Soma noted. One horse length is equal to one-fifth of a second, meaning the horse that finishes five lengths back in a two-mile race is only one second behind the winner. So even small things can make a difference.

“It doesn’t look like breeding makes all that much difference,” Soma said. Modern race horses do not have much genetic variability, because they trace their ancestry to the same 30 or so horses. Since the 1700s, horses have become a little faster, but not much, he said.

Like standing on one finger

Horses pack great speed for their size, a skill that comes in handy when you’re sharing the open plain with hungry predators. But their thin legs and relatively small hooves support a much greater proportion of weight than the human foot, which is relatively larger.

“Anatomically speaking, they run on their toes,” Soma said. “That makes them very fragile.” A human being would have to put his weight on his middle finger to duplicate the proportion of weight the horse hoof supports as it hits the ground.

The strain of a two-minute race can cause problems for horses, McKeever said. They may be unable to get enough oxygen to their tissues and carbon dioxide may build up in their blood. Blood vessels in their lungs sometimes burst from the strain and if enough burst, the horse may bleed from its nose.

Physiologists are still trying to understand why horses are susceptible to this bleeding but inhaling dust into the lungs may play a role, as may the shock produced as the horse’s 1,200 pound body lands on its legs in full gallop.

Oxygen consumption is key

Horses need a lot of oxygen when they run. They carry their own emergency supply in their spleens.

“The horse spleen is a giant bag of extra blood,” McKeever said. When the horse runs, its spleen contracts and forces a fresh supply of oxygen-rich red blood cells into its blood stream, effectively pumping extra oxygen into its cardiovascular system virtually on demand. Human athletes, on the other hand, must train at high altitude to produce a greater supply of red blood cells.

When at rest, about 35% of the total blood volume in humans and horses is comprised of red blood cells. Humans maintain that proportion even during exercise. Horses increase their red blood cell numbers to more than 65% of blood volume during a race. This greatly increases the horse’s ability to carry needed oxygen, but also makes the blood thicker. Fortunately, the horse’s heart is able to overcome this viscosity.

Horses also have a tremendous ability to use the oxygen it produces. An elite human athlete uses 70-90 milliliters of oxygen per kilogram of weight per minute, McKeever said. Thoroughbreds use more than 150 milliliters per kilogram per minute.

Any predictions?

So, should you consult your favorite physiologist before placing your bet on the Derby, or any horse race?

“We can predict the horses that will be in the top 5% of thoroughbred racing, but every horse at the racetrack is in that 5%” Birks said.” There are too many variables beyond physiology: training, diet, the jockey, horse psychology and more; and too little difference in performance between the first- and last-place finishers to be able to predict the outcome.

“We choose not to gamble,” Birks said with a laugh.

* * *

The American Physiological Society was founded in 1887 to foster basic and applied bioscience. The Bethesda, Maryland-based society has more than 10,000 members and publishes 14 peer-reviewed journals containing almost 4,000 articles annually.

* * *

APS  provides a wide range of research, educational and career support and programming to further the contributions of physiology to understanding the mechanisms of diseased and healthy states. In May 2004, APS received the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring (PAESMEM).

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2006/11/03 05:39 2006/11/03 05:39
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