the science behind melbourne cup winners.

  Trainer Gai Waterhouse with 2013 Melbourne Cup winning horse Fiorente.   AAP/Julian Smith

Trainer Gai Waterhouse with 2013 Melbourne Cup winning horse Fiorente. AAP/Julian Smith

It’s the race that stops a nation … and is worth a cool A$6.2 million. So what goes into the raceday preparation for the equine stars of the show?

Thoroughbred racehorses have unique anatomy and physiology that suits them well for racing at high speeds. There are very few 3,200m Thoroughbred races in Australia, and the horses that make it to the final 24 in the Melbourne Cup are truly elite equine athletes.

They have superior oxygen transport and an ideal mix of muscle fibre types, and are able to efficiently gallop at high speed. But winning the race also depends on how the horse behaves on the day, and of course, several ounces of good luck.

Built to win

While Phar Lap’s massive heart is an Australian legend (and is on display at the National Museum of Australia), horses racing in the Melbourne Cup will have big hearts with exceptionally high capacity for pumping blood to their muscles.

  Phar Lap’s heart … all 6.35kg of it.      Mountain/ \Ash/Flickr ,  CC BY

Phar Lap’s heart … all 6.35kg of it. Mountain/ \Ash/FlickrCC BY

During the race, each horse’s heart rate will hit 220-230 beats per minute, with each beat pumping around 1.3-1.4 litres of blood (this is called stroke volume). To put this in perspective, around 300 litres of blood will be pumped to each horse’s muscles and other tissues during each minute of the Melbourne Cup race.

That blood also has an extraordinarily high concentration of haemoglobin – its oxygen-carrying component – much higher than that of elite human athletes.

These factors combine to enable an elite racehorse to consume approximately 250 litres of oxygen during the race.

On average, horses in the Cup will consume oxygen at maximum rates of around 180ml per minute for each kilogram of body weight after the first minute of the race.

Better race results could be expected in the horses with the highest oxygen-consumption – but a win depends on more than just higher aerobic capacity. At some stage in the race every horse will need to do a short sprint, and must also possess the anatomy and physiology suited to a short burst of speed.

These elite horses will have just the right combination and number of different types of muscle cells to provide the ideal mix of endurance and acceleration.

The best Thoroughbred racehorses have higher proportions of fast twitch oxidative muscle fibres (FOG), which are well suited to fast contractions, oxygen metabolism and fatigue resistance.

In contrast, slow twitch fibres (SO) are better suited to endurance races over 50 kilometres or more.

A higher percentage of fast twitch glyolytic fibres (Type FG) provide for high speed over sprint distances of 400-1,000m.

In comparison with this year’s Melbourne Cup contenders, Black Caviar probably had a higher ratio of muscle mass to body mass, coupled with a higher percentage of Type FG muscle fibres, which provided her the ideal muscle structure and function suited to racing over sprint distances of 1,000-1,200m.

Training for a two-miler

As I said earlier, there are few races in Australia as long as the 3,200m Melbourne Cup, so training for the race needs a mix of slow and fast gallops and short distance sprints of 400-600m.

The trainer has the challenging job of making the right decisions each morning in order to promote fitness, but not overtrain and tire the horse out for a few days at just the wrong time.

While there is no science in these day-to-day decisions, the art of the trainer is still very important in preparing the individual horse to be at peak physical fitness and emotional state on the day.

(Yes, emotional state. More on that in a minute.)

  2011 Melbourne Cup winner Dunaden doing trackwork the day before the 2013 Melbourne Cup.     AAP/Julian Smith

2011 Melbourne Cup winner Dunaden doing trackwork the day before the 2013 Melbourne Cup. AAP/Julian Smith

The horse will usually have its final sprint or fast gallop workouts 3-5 days before the race before being maintained with slow exercise each day until the race – much like a human athlete tapers before a marathon.

Daily feed intake is usually decreased on the day of the race – having a big mass of food in the intestines isn’t ideal.

Horses in the Cup may have included treadmill training in their preparation for the race. Use of high-speed treadmills is now much more common in the larger training businesses, and adoption of this technology seems more common in Australia than in other countries. A treadmill is particularly useful for monitoring and maintaining a horse’s heart rate during training (see the video below).

Horses racing for the Cup must also pass an intensive pre-race inspection by experienced veterinarians, who ensure that the welfare of the horse is not compromised.

Horse psychology

Poor behaviour before or during the race can seriously impact a horse’s performance. Horses with over-excitability before the race, usually shown by agitation and excessive sweating, tend to perform less well than their calmer race mates.

I have even seen a horse so agitated before the Melbourne Cup that it had to be withdrawn because it refused to go to the starting gates.

Likewise, horses which do not relax during the running of the race pull hard against the jockey’s trying to restrain the horse. This costs energy, so the horse’s efficiency of galloping is decreased, resulting in poor performance.

Of course, there are other factors to take into account, such as the jockey and handicap.

But from a purely equine perspective, horses in the Melbourne Cup must win the genetic lottery, respond to training and racing programs over several years and be in just the right mental state on the day.


fitness tests with HR and GPS systems.

The principle of fitness testing necessitates accurate measurement of velocity of the horse. Until recently this achievement has only been possible during treadmill exercise tests. New measurements based on studies of the heart rate relationship with velocity haverecently been used successfully in field studies. Recordings are made over 5-6 gallops at least, collecting data from trotting and gallops at 600-750 m/min (16-20s/200 m) and during short sprints. These studies assist with calculation of the velocity at which the horse attains its maximal heart rate (VHRmax). The heart rate at precise submaximal gallop speeds (30-45 kph) can also be assessed. Velocity is measured with an accurate and sensitive global positioning system device carried on the horse or jockey. This technique has been used to describe changes in fitness with high speed training in two year old thoroughbreds, (7) and has been significantly correlated with racing performance in Australian (8) and Japanese studies.

7. Vermeulen A.D. and Evans D.L (2006) Measurements of fitness in thoroughbred racehorses using field studies of heart rate and velocity with a global positioning system. Proc. 7th Int. Conf. Equine Exercise Physiology, eds. Essén-Gustavsson, B., Barrey, E., Lekeux, P.M., Marlin, D.J.., Equine Vet. J. Suppl. 36; 113-117

8. H.L. Gramkow and D.L. Evans (2006) Correlation of race earnings with velocity at maximal heart rate during a field exercise test in Thoroughbred racehorses. Proc. 7th Int. Conf. Equine Exercise Physiology, eds. Essén-Gustavsson, B., Barrey, E., Lekeux, P.M., Marlin, D.J.., Equine Vet. J. Suppl. 36; 118-122

VHRmax is a measurement of high speed stamina. It represents the velocity at which there is no further increase in aerobic ATP resynthesis. Increases in velocity must therefore depend on increased rate of anaerobic metabolism, and this metabolic response is quickly followed by fatigue. It has been estimated that fatigue will ensue after approximately 600-800 metres of maximal speed gallop that involves high rates of anaerobic energy output.

Recent research b y the author has confirmed that assessment of the HR response during ubmaximal gallop exercise (15-40 kph) should be measured as well as VHRmax for a complete assessment in thoroughbred racehorses. Occasionally horses with high VHRmax do not perform well, and such poor performance could be explained by poor cardiac performance at high HRs (which can exceed 225 in some horse). For example, they could have murmurs of electrocardiographic problems could limit the cardiac output at very high HRs. Complete clinical examinations including evaluation of the EKG during exercise and cardiac ultrasound immediately after exercise can confirm such cardiac limits to performance.

In endurance horses the relationship between speed and HR can be used to guide training intensities, and evaluate future performance potential. Superior performance could be expected in horses with lower HRs during field exercise. Such lower HRs could reflect higher blood and cardiac stroke volumes, and superior economy of locomotion.

An example of simultaneous HR (top line) and velocity recording in a 3 year old thoroughbred racehorse is presented below. This horse walked at for 500 m, trotted at 18 kph for 800 m, then galloped at 38-42 kph over 3000 m. The recording was generated with a Garmin Forerunner 301 GPS system adapted for use in horses. 

Polar Equine HR+GPS systems are now recommended for use for ridden and driven horses, such as trotters and pacers.

Speed is recorded from changes in position every 2-3 seconds, and a heart rate is provided at each of the speed data points. Maps (stylised, or with Google Earth) show the position of the horse at each HR and speed recording, and show the course taken during the workout. Speed is given to the nearest 1 kph, and HR to the nearest 1 beat per minute. Records can be studied over time periods, or over distance. Peak speed during fast gallops is easily recorded. In thoroughbreds, this value can range from a low of 60 kph to over 70 kph in the best sprinters.

The principle of fitness testing necessitates accurate measurement of velocity of the horse. Until recently this achievement has only been possible during treadmill exercise tests. New measurements based on studies of the heart rate relationship with velocity haverecently been used successfully in field studies. Recordings are made over 5-6 gallops at least, collecting data from trotting and gallops at 600-750 m/min (16-20s/200 m) and during short sprints. These studies assist with calculation of the velocity at which the horse attains its maximal heart rate (VHRmax). The heart rate at precise submaximal gallop speeds (30-45 kph) can also be assessed. Velocity is measured with an accurate and sensitive global positioning system device carried on the horse or jockey. This technique has been used to describe changes in fitness with high speed training in two year old thoroughbreds, (7) and has been significantly correlated with racing performance in Australian (8) and Japanese studies.

7. Vermeulen A.D. and Evans D.L (2006) Measurements of fitness in thoroughbred racehorses using field studies of heart rate and velocity with a global positioning system. Proc. 7th Int. Conf. Equine Exercise Physiology, eds. Essén-Gustavsson, B., Barrey, E., Lekeux, P.M., Marlin, D.J.., Equine Vet. J. Suppl. 36; 113-117

8. H.L. Gramkow and D.L. Evans (2006) Correlation of race earnings with velocity at maximal heart rate during a field exercise test in Thoroughbred racehorses. Proc. 7th Int. Conf. Equine Exercise Physiology, eds. Essén-Gustavsson, B., Barrey, E., Lekeux, P.M., Marlin, D.J.., Equine Vet. J. Suppl. 36; 118-122

VHRmax is a measurement of high speed stamina. It represents the velocity at which there is no further increase in aerobic ATP resynthesis. Increases in velocity must therefore depend on increased rate of anaerobic metabolism, and this metabolic response is quickly followed by fatigue. It has been estimated that fatigue will ensue after approximately 600-800 metres of maximal speed gallop that involves high rates of anaerobic energy output.

Recent research b y the author has confirmed that assessment of the HR response during ubmaximal gallop exercise (15-40 kph) should be measured as well as VHRmax for a complete assessment in thoroughbred racehorses. Occasionally horses with high VHRmax do not perform well, and such poor performance could be explained by poor cardiac performance at high HRs (which can exceed 225 in some horse). For example, they could have murmurs of electrocardiographic problems could limit the cardiac output at very high HRs. Complete clinical examinations including evaluation of the EKG during exercise and cardiac ultrasound immediately after exercise can confirm such cardiac limits to performance.

In endurance horses the relationship between speed and HR can be used to guide training intensities, and evaluate future performance potential. Superior performance could be expected in horses with lower HRs during field exercise. Such lower HRs could reflect higher blood and cardiac stroke volumes, and superior economy of locomotion.

An example of simultaneous HR (top line) and velocity recording in a 3 year old thoroughbred racehorse is presented below. This horse walked at for 500 m, trotted at 18 kph for 800 m, then galloped at 38-42 kph over 3000 m. The recording was generated with a Garmin Forerunner 301 GPS system adapted for use in horses. 

Polar Equine HR+GPS systems are now recommended for use for ridden and driven horses, such as trotters and pacers.

Speed is recorded from changes in position every 2-3 seconds, and a heart rate is provided at each of the speed data points. Maps (stylised, or with Google Earth) show the position of the horse at each HR and speed recording, and show the course taken during the workout. Speed is given to the nearest 1 kph, and HR to the nearest 1 beat per minute. Records can be studied over time periods, or over distance. Peak speed during fast gallops is easily recorded. In thoroughbreds, this value can range from a low of 60 kph to over 70 kph in the best sprinters.


lactate measurements in equine sport science.

Accumulation of lactate in muscle cells and in the blood is a normal consequence of fast exercise in the horse. At low speeds, the horse is able to generate sufficient energy by catabolism of glycogen, glucose and fat. This metabolic process uses oxygen to generate ATP, and is referred to as aerobic. At higher speeds, aerobic metabolism does not regenerate ATP quickly enough. Pyruvate accumulates in muscle cells, and it is converted to lactate ions at increased rates.

Exercise at speeds greater than approximately 700–800 m/min recruits fast twitch skeletal muscle fibers. These fibers can be classified as being highly oxidative or highly glycolytic in nature. At fast speeds, recruitment of fast twitch, highly glycolytic muscle fibers results in accumulation of lactate anions and hydrogen ions in the muscle cells, due to the contribution of anaerobic glycolysis to ATP resynthesis. Both these ions diffuse into the extracellular fluid. It is generally thought that the stimulus for anaerobic glycolysis in skeletal muscle fibers during fast exercise is a limitation to the supply of oxygen at the cellular level.

The production of many molecules of lactate and hydrogen ions results in acidosis of both the skeletal muscle cells and the blood. The increasing acidity of muscle cells is implicated in fatigue during intense exercise, but the direct cause and effect is still debated. In any horse at top speed for about 800 m, the accumulation of lactate and the concomitant cellular acidosis has a negative effect on energy production by anaerobic glycolysis. The rate of ATP production is decreased, and the animal reduces speed.

Resting blood lactate concentration in the horse is approximately 1–1.5 mmol/L. At low speeds this value does not change greatly from the resting value. At moderate speeds lactate begins to accumulate in the blood. Accumulation of lactate in blood occurs most quickly when the work speed is faster than that at which blood lactate is about 4 mmol/L. This work speed at which blood lactate is 4 mmol/L is often referred to as the anaerobic threshold, or the speed at onset of accumulation of blood lactate (OBLA). It is also frequently referred to asVLa4. VLa4 is therefore the work velocity which results in a blood lactate of approximately 4 mmol/L. This value is derived from inspection of graphs of exercise speed (on the X axis) plotted against blood lactate concentration (on the Y axis). The rate of lactate accumulation generally parallels the accumulation of adrenaline in the blood.

At speeds greater than VLa4, lactate accumulates rapidly in the blood. The general relationship between velocity and blood lactate is therefore usually described as exponential. However, if sufficient steps are used in the exercise test, the relationship is described by two straight lines, with an obvious velocity at which the blood lactate begins to accumulate in blood.

After a race, blood lactate concentrations are usually greater than 20 mmol/L. It is normal for the blood and muscle lactate concentration to then gradually decrease over a 1–2 h period after a race or fast work. Acidosis of muscle and blood is a normal result of fast work, and this acidosis is rapidly reversed by the horse’s own metabolism. Racehorses do not develop chronic acidosis due to lactate accumulation in training, and therefore alkaline supplements are not required.

The rate of decrease in blood lactate after exercise is affected by the activity during this period. For example, blood lactate decreases more quickly after strenuous exercise if the horse is trotted for 3 0minutes, rather than walked. However, such a practice might delay cooling of the horse.

Many studies of horses trained on both treadmills and on racetracks consistently demonstrate that training results in lower blood lactate concentrations at the same work speed. The speed at which blood lactate begins to accumulate rapidly, VLa4, also increases. The horse is able to work at a higher speed without accumulating lactate.

Repeated tests of the blood lactate relationship with velocity are suitable as a means of measuring increasing stamina with training. If more than one horse is tested, measurements of VLa4 enable comparisons of the relative stamina in each horse. VLa4 measurements every 2–3 weeks also enable measurement of changes in fitness through the training program. However, VLa4 measurements have the disadvantage of requiring several blood collections and analyses. A simple, one step exercise test can be designed to give the same information. For example, the blood lactate concentration 3 minutes after a two minute gallop on a treadmill was correlated with racing performance in thoroughbreds (Evans et al., 1993). The exercise test for race-fit horses was as follows. The treadmill angle was set at 6° (or a 1 in 10 slope). The horse is trotted for 2 min (at 4 m/s), followed immediately by 2 min slow cantering (6 m/s). The horse is then walked on the treadmill for 4 min, and then given 2 min exercise at 10 m/s. Racehorses with superior stamina, or endurance fitness, have blood lactate concentrations of <4 mmol/L after the test.

The blood lactate response is therefore a guide to racing ability, and the other factors which contribute to racing success must not be ignored. However, a treadmill study of 12 English Thoroughbred racehorses indicated that 47% of the variability in Timeform rating (a handicap rating system) was due to variability in their blood lactate response to treadmill exercise, using a test similar to that described above. The better horses had a lower blood lactate after treadmill exercise at 10 m/s on a treadmill inclined at 10%. Similar results have been reported in trotting horses. The blood lactate response to exercise is a very important determinant of likely success or failure on the racetrack.

When blood is collected for lactate assays, it should be added to tubes containing a suitable anticoagulant and inhibitor of glycolysis. Fluoride and oxalate combinations are suitable, as the blood stores well at room temperature for at least two days in those chemicals. However, if possible, blood should be stored in a refrigerator or on ice until analysis. Individual laboratories should be consulted concerning ideal storage conditions, as different centres use different techniques to conduct the analysis.

Lactate assays can also be conducted on plasma. However, plasma and whole blood lactate concentrations in blood collected after exercise are not equivalent. Plasma lactate concentrations are 140–150% of concentrations found in whole blood, due to unequal distribution of lactate between plasma and erythrocytes in horse blood after exercise rainger etal., 1995). Plasma and whole blood lactate concentrations should therefore not be directly compared.

In the past, lactate assays have been complicated and not readily available. The analysis of plasma or serum for lactate concentration has been greatly simplified by the development of rapid analysers. However, these technologies should be used with great caution. They express a value for blood lactate, but blood lactate is not directly assayed. The assay is of plasma lactate, and if haematocrit exceeds 50% large errors occur. (Evans and Golland 1996). After exercise haematocrit will usually exceed 50% in horses.

Incremental treadmill exercise tests, with measurements of heart rate and blood lactate at various speeds, can also be conducted. Such tests enable calculation of indices of fitness such as V200 and VLa4. Collection of blood at each speed necessitates stopping the treadmill after each step, or placement of an IV catheter. Sterile heparinized saline solutions can be used to maintain catheter patency during the tests. Such tests are now common at research centres with treadmills for assessment of poor performance. Measurements of heart rate, blood lactate and oxygen consumption are usually conducted during submaximal exercise and during exercise at maximal intensities. However, blood lactate concentrations after maximal exercise have not been correlated with racing performance.

Blood lactate measurements after field exercise are not advisable for assessments of fitness in thoroughbreds. Small variations in speed or distance of the gallop can have large effects on the post-exercise blood lactate concentration.

Blood lactates after exercise have been recommended for guiding the training intensity. A recent study found no difference to the aerobic fitness produced after training at lactate concentations of 2 or 4 mmol/L. However, post exercise blood lactates may be useful for guiding training at higher intensities. It is known that muscle adaptations to training occur at 80-100% of HRmax. At these intensities PLASMA lactate concentrations immediately after exercise could be expected to be in the range 10-15 mmol/L.


training to avoid injury.

Training to avoid injury: 

Many recent studies of adaptations to exercise and training have demonstrated that tendons, cartilage, bone and other musculoskeletal structures do adapt to the stimulus of regular exercise, or training. In young horses adaptations have been demonstrated, and these changes could help prevent injury during their racing careers in later years. Epidemiolgical studies have shown that racing success is dependent on the volume of exercise training, but there are also limits to the speeds and durations of exercise that can be sustained without resultant injury. It has also been demonstrated that the rate of increase in distances at high speeds is also an important risk factor for lameness, with higher rates resulting in higher risk. Exercise programs have also been used to prevent development of osteochondrosis. The overall conclusion is that exercise programs in young horses, coupled with low-risk training strategies in older horses, can reduce the risk of injury.


treadmill exercise tests.

In this paper 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


training for superior fitness and fatigue resistance.

Preparation of racehorses for racing necessitates gradual increases in the speed of exercise. It is only at exercise intensities near maximal that improvements in anaerobic capacity and anaerobic power can be expected. Lactic dehydrogenase (LDH) concentration in skeletal muscle has been used as a marker of anaerobic enzyme activity. Interval training at high speeds on a treadmill resulted in increased concentration of LDH in skeletal muscle, but conventional training does not have the same effect (9). Likewise, training at a moderate intensity (80% of VO2max) for 6 weeks does not result in increases in skeletal muscle (gluteus medius) LDH concentration, although that training did increase the muscle buffering capacity by 8% and increase the ratio of fast twitch highly oxidative fibres to fast twitch fibres (FTH/FT) (10).

These adaptations to training did not occur in a group of horses trained concurrently at a lower intensity of 40% VO2max. Intensity of training is therefore an important factor in determining the degree of local adaptations in skeletal muscle.

There is some evidence that prolonged periods of endurance training stimulate continued adaptation of skeletal muscle. The activities of two enzymes, used as markers of oxidative capacity of muscle, continued to increase throughout a nine-month training program in endurance horses (11).

A study of effects of training and detraining on muscle physiology also confirmed the importance of prolonged training, and avoidance of prolonged detraining unless absolutely essential (12). Twenty-four 4-year-old Andalusian (Spanish breed) stallions were used to examine the plasticity of myosin heavy chain (MHC) phenotype and the metabolic profile in horse skeletal muscle with 8 months endurance-exercise training and 3 months of detraining in a paddock. Long-term changes with training were an increase of slow MHC-I, increases of high-oxidative fibres, capillary density, activities of aerobic enzymes and endogenous glycogen. Intramuscular lipid deposits also increased after 8 months of training, whereas the activities of anaerobic enzymes declined. Most of the exercise-induced alterations reverted after 3 months of detraining. The results also found a dose-response relationship between the duration of training and the magnitude of muscle adaptations. As training duration increased, so did the adaptations in the muscle. The results also infer that the capacity for anaerobic metabolism of muscle cells is reduced by prolonged, low intensity training. This response could reduce a horse's ability to accelerate, and reduce maximal speed and jumping ability. Such a response is of little relevance to an endurance horse, but in horses racing over 800-32000 metres, and in eventers, specific additional training should be used to promote anaerobic and buffering capacities of skeletal muscle.

These key references illustrate the importance of designing training programs that help trainers use appropriate training intensities, and which help trainers keep their horses in training to maximise the long term responses. Appropriate blood lactate and heart rate measurements are the measurements that can provide the necessary guidance.

9. Lovell DK, Rose RJ: Changes in skeletal muscle composition in response to interval and high intensity training. In Persson SGB, Lindholm A, Jeffcott LB, eds.: Equine Exercise Physiology 3, Davis: ICEEP Publications, 1991, p. 215.

10. Sinha AK, Ray SP, Rose RJ: Skeletal muscle adaptions to different training intensities and to detraining in different hindlimb muscles in thoroughbred horses. In Persson SGB, Lindholm A, Jeffcott LB, eds.: Equine Exercise Physiology 3, Davis: ICEEP Publications, 1991, p. 223.

11. Hodgson DR, Rose RJ: Effects of a nine month endurance training program on skeletal muscle composition in the horse. Vet Record 121:271, 1987.

12. Serrano AL, Quiroz-Rothe E, Rivero JLL: Early and long-term changes of equine skeletal muscle in response to endurance training and detraining. Eur. J. Physiol. 441:263, 2000.


performance based selection of athletic horses.

One of the earliest themes in exercise physiology of horses was the selection of physiologically superior athletes. The concept of using a measurement that accurately predicted success in racing or other athletic events is still popular. In this session a review will be presented of the methods that have been used more recently. What is being measured? What is the evidence for those measurements?

Selection of horses based on a physiological measurement has usually focussed on cardiac measurements. Electrocardiographic assessment of heart size was popular for decades, and now cardiac ultrasound is used by some investigators. Muscle biospsies for assessment of fibre type distribution were briefly popular, but results are unreliable for racehorses.

There is good rationale for focus on the heart. Athletic performance depends on aerobic and anaerobic energy supply. The dependence on aerobic ATP resynthesis is higher in events with longer duration. It has been estimated that all thoroughbred races with durations exceeding 1000 m have greater dependence on aerobic than anaerobic energy supply. In a race with 2-3 minutes duration, aerobic energy might supply 70-80% of the total requirement.

Assessment of anaerobic energy output in human athletes usually relies on 30 second bicycle or treadmill test of maximal energy output. No such equivalent test exists for horses, and more research is needed in this area.

Aerobic energy output is predicted by the Fick equation

Oxygen uptake = (HR x stoke volume) x peripheral oxygen use

Assessment of heart structure with cardiac ultrasound in a resting horse as part of an examination to predict future performance attempts to predict stroke volume during exercise. This is a large extrapolation from resting measures of cardiac wall mass, end-diastolic volumes and indices of contractility. As well, indices of cardiac myocardial wall function during ultrasound depend on HR. Other factors that could limit the accuracy of cardiac ultrasound to predict cardiac output at maximal exercise intensities include;

Absence of the effects of increase in blood volume due to splenic contraction

Cardiac contractility during high HRs

Effects of training is very different in individual horses

Measurements are not expressed relative to horse body weight or age – a serious limitation

Absence of maximum HR (varies by up to 15%), so excludes estimate of maximum cardiac output

Maximal heart rate can vary from 195 to 235 beats per minute, so in horses with the same sized heart, the blood blow from the heart during a race can vary by 20%. Assuming a stroke volume of 1.3 litres, the range of HRmax can explain a range of cardiac output of 50 litres per minute! This variation shows the difficulty of trying to predict future performance with cardiac ultrasound in yearlings to assess heart size. Of course the changes in the heart’s ability to pump blood is also likely to vary greatly between horses as they grow, train and exercise, due to differences in genetics, and changes in myocardial structure and function (contractility).

In human athletes, there is evidence to support a link between left ventricular mass and VO2max. It has also been suggested that VO2max correlates to athletic performance in horses. However, there was no a relationship between left ventricular size and VO2max in 6 Thoroughbreds exercising on a treadmill. However, this and most other studies focussed on flat race Thoroughbreds or Standardbreds that generally run over distances of less than 3,200 m (2 miles).

More recently a strong relationship between left ventricular mass and other measurements of cardiac size with VO2max was reported in a group of 18 Thoroughbred racehorses exercising on a high-speed treadmill (Young et al, 2002). VO2max was significantly correlated with left ventricular (LV) internal diameter in diastole (r=0.71; P=0.001), estimated LV mass (r=0.78; P=0.0002) and LV short-axis area in diastole (r=0.69; P=0.003). When indices of heart size were indexed to body weight the correlation between VO2max and indices of heart size were lower or similar, (LV diastolic diameter (r=0.57; P=0.01), LV mass (r=0.78; P=0.0002) and LV short-axis area (r=0.69; P=0.003).

Whilst a relationship between left ventricular dimensions and VO2max had been established, whether a similar relationship existed for heart size and athletic performance was still in doubt: However, recent data from a large cross-sectional study of racehorses competing on the flat or over jumps in the United Kingdom did demonstrate a relationship between derived left ventricular mass and published rating (quality) in horses racing over longer distances in jump races (P£0.001), although the strength of the association with left ventricular mass was less for horses in flat races (Young et al..). Rather, left ventricular ejection fraction and left ventricular mass combined were positively associated with race rating in older flat race horses running over sprint (<1408m) and longer distances (>1408 m), explaining 25-35% of overall variation in performance, as well as being closely associated with performance in longer races over jumps (23%). Predicted differences between otherwise equivalent horses with small and large hearts was thus able to explain a significant proportion of the difference between elite and non-elite racehorse performance (Evans and Young, 2010).

However, these results conflict with findings in 370 Thoroughbred yearlings, where there was no relationship between echocardiographic measurements of heart size and prospective race performance (Leadon et al., 1991).

Use of echocardiography to predict future performance of racehorses should nevertheless still be used with caution, because the relative proportion of energy supply from aerobic metabolism probably varies widely. For example, in Thoroughbred races, with a range of 800-3200 metres distance, the relative contributions of aerobic energy output could be 40-80%. With the possible exception of horses used for high level endurance riding, the technique is also likely to have limited value for horses other than those that race, as other skills are likely to be equally or more important influences on their athletic success than aerobic capacity. Additionally the level of skill required to obtain repeatable images of the equine left ventricle with an echocardiograph for this purpose is high and the confounding effects of gender, fitness, age and body size must always be taken into account. Prediction of maximal cardiac output and maximal oxygen uptake from estimates of stroke volume in a resting horse will be also confounded by variation in maximal heart rates during exercise.

Success of endurance horses will depend on superior aerobic fitness and economy of locomotion, reflected in lower HRs during exercise.

Muscle biopsies have also been investigated for prediction of endurance horse performance (Rivero et al.) . The disadvantage of muscle biopsies is their invasive nature, but a combination of muscle biopsy with assessment of heart rates during exercise should offer the best opportunity for accurate assessment of athletic potential in endurance horses.

What is the future for performance prediction if cardiac ultrasound measurements at rest are inaccurate. More studies are needed to investigate the use of heart rate and blood lactate measurements during field and treadmill exercise. Such studies will necessitate use of large numbers of commercially trained horses, with assessments scheduled during exercise undertaken before their first races. Treadmill or other mechanical testing equipment offers a methodology for such studies.

DNA analysis?

New commercial services offering genetic testing are now marketed. Each service should be scrutinised carefully for the evidence that supports the product, and thought given to the limitations of the service.

For example, a service that only estimates sprint capacity is probably ignoring a very important factor in the performance of most athletic horses; their aerobic capacity.

References

Evans D.L. and Young, L (2010) Cardiac responses to exercise and training. In: Cardiology of the Horse. Editor Marr, C. M., published by Elsevier Saunders, London

Young LE. Diseases of the heart and vessels. In: Hinchcliff KW, Kaneps AJ, Goer RJ, editors. Equine Sports Medicine and Surgery: Basic and Clinical Sciences of the Equine Athlete. Edinburgh: WB Saunders; 2003. p. 728–769.

Sampson SN, Tucker RL, Bayly WM. Relationship between VO2max, heart score and echocardiographic measurements obtained at rest and immediately following maximal exercise in thoroughbred horses. Equine VetJ Suppl 1999;30:190–194.

Young LE, Marlin DJ, Deaton C, Brown-Feltner H, Roberts CA, Wood JLN. Heart size estimated by echocardiography correlates with maximal oxygen uptake. Equine Vet J Suppl

2002;34:467–472.

Leadon D, McAllister H, Mullins E, Osborne M. Electrocardiographic and echocardiographic measurements and their relationships in Thoroughbred yearlings to subsequent performance. In: Persson SGB, Lindholm A, Jeffcott LB, editors. Equine Exercise Physiology 3. Davis, CA: ICCEP Publications; 1991. p. 18–22.


overtraining.

Training and overtraining:

5.1. Overtraining can be defined as an imbalance between training and recovery. Overtrained animals appear fatigued. Their performance deteriorates and they may lose weight. Short-term overtraining can be corrected by rest for a period of days to weeks. If the severity of the overtraining is greater, a recovery period of several months is required.

Overtraining appears to be associated with dysfunction in the neuroendocrine system. The blood cortisol response to intense exercise is reduced in overtrained horses. The syndrome is not associated with exhaustion of the adrenal glands. Rather, there is a downregulation of the hypothalamic response to the exercise stimulus. 

The syndrome cannot be diagnosed by routine haematology or biochemistry in resting horses.