EXCERCISE AND TRAINING OF TROUGHBREDS
A report for the Rural Industries Research and Development Corporationby David L. EvansDepartment of Animal ScienceUniversity of Sydney
The article is an extract of the book on Horse Training which will be beneficial for understanding the subject on Training of Horses.
IntroductionTraining.
Involves the use of regular periods of exercise to promote changes in the structure and function of the animal in order to enable it to compete more effectively. Adaptations occur in the cardiovascular system, muscle cells, and in the structural elements such as tendons and bone. An efficient training response depends on the use of appropriate training stimuli. The appropriateness of the training stimulus necessitates consideration of the following questions:
1.At what age should training commence?
2.How fast should the horse exercise?
3.Over what distance should the horse exercise?
4.What type of exercise should be used, considering gait, and use of swimming, treadmill exercise, and jumping?
5.How is the intensity of the training stimulus best measured?
6.Is the training stimulus adequate to produce an adaptive response in the horse?
7.Is the training stimulus inadequate (undertraining), or is it too intense (overtraining)?
8.Over how many weeks should the horse be prepared prior to competition?
9.How many weeks should be used for training at slow speeds during the first phase of training?
10.How often should the horse perform at speeds at or near racing or competition speeds?
11.How often can the horse be exercised at strenuous submaximal speeds (approximately 70-90% of maximal speeds)?
12.How can a trainer judge or measure whether or not the training is resulting in a change in fitness?
13.What are the signs of overtraining in horses?
14.Is the horse mentally prepared for competition?
15.Is the horse likely to behave in a way that will maximise, or at least not limit, performance?
There are, of course, many other questions that need to be addressed during training of horses. These relate to education and behaviour of the horse, and its transport, diet and stable management. Strategies for “keeping the horse happy” should not be underestimated, and much of the art of training involves maintaining the horse’s keen attitude over many weeks of training and racing.Most trainers manage to conduct their businesses without consciously considering the above questions each day. However, many have learned answers to the questions, either by observation of other trainers, or by trial and error. It is important to realise, however, that although science has helped us to better understand the answers to many of these questions, there will never be a recipe for ideal training. The large differences between Thoroughbred training techniques in England, United States and Australia illustrate that there are many paths to training success.
Training for each horse should be individualised, according to each horse’s own temperament, and capacity for exercise. It must also take into account the event that the horse is being prepared for. However, regardless of whether a horse is being prepared for a 1200 meter two year old Thoroughbred race or 160 kilometre endurance ride, there are several principles of training that, if not followed, lead to undertrained or overtrained horses. Both of these states limit performance, and waste an owners time and money. A common problem in horse training is a period of ‘over-reaching”. This term refers to a condition found in horses that have had a sudden increase in training speeds or distances, or have been entered in competition before they are fully prepared. The sudden increase in intensity of exercise causes a sudden increase in stress on bone, tendons and other structures, and there may be injuries as a result. After the exercise or race, horses are often slow to recover, and have a poor appetite.
If horses are continually trained at high speeds, a more serious condition can occur, called overtraining. This state can be likened to chronic fatigue. Overtrained horses race poorly, lose weight, and cannot be kept in training. They must be given a prolonged spell to recover. Lameness due to inflammation or damage to musculoskeletal structures (muscle, tendons, ligaments, cartilage) is a daily concern of trainers, probably more so than the fitness of the animal. Many trainers use training techniques that are designed to reduce lameness, rather than increase fitness. Many trainers are fearful of more strenuous training programs because of perceptions that they will result in more lameness. Unfortunately it is likely that easy training, and training that does not provide for gradual adaptation of the fitness and strength will increase injury rates rather than decrease them.
Wilson and Robinson (1996) have reviewed risk factors for equine racing injuries, with a focus on overseas racing. They observed that despite the long history of horse racing, only recently have studies enumerated and elucidated the risk factors for racing injuries. They also state that many industry observers believe that the overall number of injuries has increased rather than decreased in spite of medical and surgical advances in diagnosis and treatment during the past decade. As well, the authors expressed the view that if the horse racing industry in the United States was able to design an economically feasible method for minimizing race-related injuries, the high injury rate that occurs on U.S. racetracks could be considerably reduced.
Training practices, the frequency of speed work, racetrack surface and condition, age, and the presence of preexisting lesions have emerged as important factors in injury occurrence (Wilson and Robinson, 1996).
In addition, new links between nutrition and injuries have also been identified. The authors also note that there have been declines in injury rates in Japan and Great Britain following implementation of recommendations to improve racing safety. The following sections outline the general principles of training. Where appropriate, scientific studies that have provided evidence for or against certain training strategies will be included. Unfortunately there have been insufficient studies to help us answer all the questions relevant to training. Equine training studies are very expensive and time consuming, and it is difficult to conduct experiments that compare the effects of different
Approaches to training on performance or injury rates. Large scale studies of normal populations of horses in commercial training will help answer these questions in the future.
Types of training used for horsesTraining of horses should follow several important principles.
Firstly, all horses will need to complete a period of base training. In the past, this type of training has been referred to as aerobic training, endurance training, and long, slow distance training. In this section these terms will be avoided. All forms of exercise involve some aerobic and anaerobic component. The term “long, slow distance” implies that horses only do very long distances at slow speeds. Endurance training involves use of base training techniques for many months in order to prepare a horse for an endurance race. Three day event horses should also undertake extensive base training, but they also need other training methods.During initial training of a racehorse and event horse it is important that the stimulus does not remain the same from week to week. Every 10-14 days, the speed of the exercise and or the distance should be increased. This increase promotes gradual adaptation of the muscles, tendons, and bones, enabling structural changes that help the animal cope with increased demands of higher speed work. In the author’s opinion, many problems in racehorse preparation can be attributable to failure to gradually increase the training stimulus. One day the horse is trotting and slow cantering, and on the next day it is exercising at a strong half pace (about 600 metres per minute). Thoroughbred horses also frequently go from trot and canter work on pre-training farms to exercising at three quarter pace or faster (working gallops) on racetracks with very little exercise at intermediate speeds. Sudden increases in velocity place the support structures (bone, tendon and muscle in particular) under great stress, and under such conditions there is often failure of the structure to resist the strain imposed. The result is seen in sore shins and sprained fetlocks, especially in two year old Thoroughbreds.
Basic training will be used to describe training at speeds of 200-approximately 500 and 600 metres per minute in Standardbred and Thoroughbreds.Strenuous trainingwill be used to describe training at speeds higher than 600 metres per minute that results in accumulation of lactate in the blood, but at slower than racing speeds. Sprinttrainingrefers to exercise at or near racing speeds.Interval trainingrefers to use of multiple exercise bouts, separated by rest periods for partial recovery.
Skills development refers to use of training techniques that increase the ability of the horse to complete a task.Cross training refers to use of exercise that is not specific to the event performed, such as swimming.Recovery days are days designated for recovery after races or hard training. They enable restoration of energy stores (glycogen) and repair of minor injuries.If a horse is not racing or competing, a horse trainer should be able to identify one or more of the above training types on every training day in a horse’s preparation. Other training types, such as fartlek and resistance training, are rarely used in horse training. Fartlek training has been defined as “an unstructured technique...the horse is allowed to run as far and at whatever submaximal speed it wishes (within reason)”. Indefinite relief periods are followed by more such exercise (Bayly, 1985). Resistance training refers to use of exercises where muscle groups work against resistance, as in weight lifting. An example in horses is walking with large weights carried. A recent study in two ponies found that 8 weeks of progressive resistance exercise training increased the strength and size of forelimb muscles (Heck et al., 1996). The ponies carried lead over the wither while walking on a treadmill three days per week. Ponies performed a series of progressive sets of weight carrying to fatigue. After training, ponies were able to carry more weight until the point of fatigue, and there was a 19% increase in forelimb cross sectional diameter.
Basic training. Basic training involves exercise at low intensities. Such exercise at speeds of about 3-8 m/s (200-500 metres/minute) usually results in heart rates of less than about 180 beats/min, and little or no accumulation of lactate in the blood. The only equine event that may not need a period of base training is dressage. In this case, the exercises undertaken during the dressage training should suffice for fitness development. This approach also has the important advantage of using the nerves and muscle groups that will be used in competition. As a result, dressage training results in specific adaptations in the muscles used in competition.
Basic training of all other horses may involve 5 minutes to several hours of exercise each at the trot and/or canter, depending on fitness, environmental conditions, time available, and the aims of the training.
Low intensity base training is usually employed in the first weeks or months of all training programs. Such training is designed to improve the aerobic capacity and limb strength, and to educate the horse. The duration of this "pre-training" varies markedly between breeds, countries and trainers. Some Thoroughbreds in Australia undergo only 4-5 weeks of slow training before moving on to faster exercise. In England, two months of basic training would often be used, and frequently involve use of repeated slow canters up hills. Use of many months of distance training before commencement of faster exercise in Thoroughbred and Standardbred horses has been advocated (Ivers, 1983). The principal argument for longer periods of low intensity training is the development of stronger limbs and consequent reduced frequency of limb injury. Anecdotal evidence suggests that the incidence of injuries is lower in horses that have undertaken more slow training. Shin soreness, or bucked shins, is a common problem in the training of young horses, especially Thoroughbreds (Nunamaker et al., 1990). There is a lower incidence of the disease in horses which do not undergo rapid race preparations (Buckingham and Jeffcott, 1990). 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 (Hodgson and Rose, 1987). The implications of prolonged periods of endurance training for improvements in maximal aerobic capacity have not been reported.The main limitations to endurance training in horses are time available and hot humid environments. The first priority is allowing sufficient time for the horse to sleep and eat. Care must be taken when increasing distance or speeds of exercise in endurance horses, especially on hot humid days. Deaths and extreme fatigue (exhausted horse syndrome) of horses at endurance rides illustrate that they willingly exercise for periods which result in extreme dehydration and electrolyte imbalance.
Fit Standardbred racehorses often trot or slow canter for 30-40 minutes on "slow" days. Fit Thoroughbred horses might trot or canter for 5-10 minutes over 3,000-5,000 m, and endurance horses often exercise for several hours.Heart rate meters have been used to ensure that the training intensity is not excessive. Heart rates greater than 180 beats per minute may result in accumulation of lactate in horses early in their base training.
Treadmills can be used to help with the base training of horses. Exercise at 200-450 metres per minute can be used on a treadmill inclined at 10%. Many studies of the adaptations of horses to training have used treadmills exclusively. A summary of different treadmill training protocols follows. Interestingly, in one study, treadmill trained horses earned more from prize money than non-treadmill trained horses (Kobluk et al., 1996).In the author’s experience, appropriate treadmill training coupled with track work over a period of 6 weeks provides an excellent base training.
The following training scheme was used successfully as base training in approximately 15 Thoroughbreds aged three years or older. None of these horses suffered limb injury in the program, and two horses went on to win metropolitan races in Sydney and Brisbane at their first starts. All horses completed 3 sessions of exercise per day on 6 days per week.
Session 1 involved trotting beside a jog cart on a 600 metre track, with no rider.
Session 2 was ridden exercise on a racetrack (Canterbury, Sydney), and session 3 involved treadmill exercise, with the treadmill always at 10% slope. Horses had access to food and water between sessions 2 and 3. All distances are metres. Slow, medium and fast canters (SC, MC, FC) in session 2 refer to speeds of approximately 400, 500 and 600–650 metres per minute (maximum 18 seconds per furlong).Table 1.A basic training program for Thoroughbreds using a combination
Strenuous trainingPreparation of racehorses and event horses for racing or competition necessitates gradual increases in the speed of exercise. Horses racing over 400-4000 metres and the cross country phase of the second day of a three day event all result in accumulation of lactic acid in muscle cells, and in the blood. This implies that some anaerobic metabolism is involved in the ATP resynthesis during the competition or race. It is likely that anaerobic metabolism in a Quarter horse race supplies most of the ATP. In events of 1000-4000 meters distance, anaerobic metabolism probably only supplies 20-30% of the energy (Eaton et al., 1995). Endurance rides do not stimulate anaerobic glycolysis, and training of endurance horses should involve continuation of the base training described above. Lactate 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 (Lovell and Rose, 1993). In this study Thoroughbred horses were trained for 12 weeks. In the final 3 weeks, horses exercised at a velocity that resulted in 100% of maximal heart rate on 3 days per week, over 600 metres. Speeds of exercise were 9-12 m/s on a treadmill inclined at 10%. Three bouts of exercise were given, separated by recovery periods that were three times the duration of the 600 metres of exercise. On three other days, horses exercised over 3000-4000 metres at 6-7 m/s (a canter). Total distances exercised in the three weeks of training were 18, 20 and 16 kilometres.
Training at a moderate intensity (80% of VO2 max) for 6 weeks did not result in increases in skeletal muscle (gluteus medius) LDH concentration. However, such training did significantly increase the muscle buffering capacity by 8% and increase the ratio of fast twitch, highly oxidative fibres to fast twitch fibres (FTH/FT) (Sinha et al.1991). These adaptations to training did not occur in a group of horses trained concurrently at a lower intensity (40% VO2 max). As well, there was no difference in increases in maximal oxygen uptake between the two groups (Knight et al., 1991).In summary, strenuous training is designed to stimulate anaerobic glycolysis, but also to manage the training so that fatigue does not occur.
Controlled exposure of the horse to exercise that results in moderate increases in blood lactate concentration should:
1.Stimulate contractions in fast twitch muscle cells, and promote their growth by synthesis of more contractile proteins.
2.Increase concentrations of the enzymes that regulate glycolysis, such as lactate dehydrogenase.
3.Promote increased buffering capacity in the fast twitch cells. Higher buffering capacity enables the fast twitch cells to limit the fall in pH during fast exercise, and so resist fatigue.
4.Promote the potential for the muscle cells to use lactate as a fuel during exercise.It is possible that changes in training strategies, such as interval training at intensities near maximal, could result in beneficial adaptations in muscle. Such training necessitates careful monitoring of the intensity of exercise. Exercise at sub-optimal intensities will limit the rate of adaptation, and frequent training at intensities above optimal will risk onset of fatigue and overtraining syndrome.The exercise intensity during initial weeks of training is probably not an important determinant of the rate of change in VO2 max. There was no difference in the changes in V.O2max with training in two groups of horses trained at 40% and 80% of VO2 max(Knight et al., 1991). Intensity of training may therefore be an important factor in determining the degree of local adaptations in skeletal muscle, but not for increases in maximal oxygen consumption. Heart rate meters have been suggested as a tool for monitoring the intensity of strenuous submaximal exercise. For example, exercise speed resulting in a heart rate of 200 beats/minute has been suggested as suitable for race training (Gysin et al., 1987). However, there have been no controlled studies that have confirmed this view. As well, the blood lactate concentrations at intensities that result in a heart rate of 200 beats/minute vary greatly. In unfit horses, exercise at heart rates of 200 beats/minute is likely to result in high blood lactate concentrations, and in fit horses such exercise may result in relatively low blood lactate concentrations. The metabolic response to exercise at a heart rate of 200 beats per minute can therefore be highly variable.
There are also practical difficulties in the use of heart rate meters during exercise in galloping horses. It is difficult for jockeys on Thoroughbred racehorses to monitor heart rate and adjust speed accordingly. The maximal heart rate of some horses is also 210-215 beats/min, only 5% greater than 200. As well, muscular adaptations, such as increases in LDH concentrations, may not be optimal unless exercise is at speeds that result in maximal heart rate (Lovell et al., 1991). Measurement of blood lactate after exercise is the best method of monitoring the intensity of exercise during the strenuous training phase. The appropriate intensity of exercise for strenuous training is that which results in a blood lactate concentration of approximately 4-8 mmol/L at 3-5 minutes after exercise.
If set speeds are used for all horses, some horses could be exercising with blood lactates of 2-3 mmol/L, and be undertraining. Others could be exercising with blood lactates of 15-20 mmol/l, and be overtraining. For example, that Standardbred horses that pace over 1600 metres in 130 seconds (halves in 7.5 seconds) have plasma lactates in the range 2-15 mmol/L (unpublished data). The metabolic demands imposed by the exercise are very different in the horses exercising at intensities that result in plasma lactate concentrations of 2 and 15 mmol/L.How often should horses exercise in order to obtain a training effect? There have been very few studies of this question. However, Gottliebvedi et al. (1995 found that interval training at VLa4 on only three days per week is sufficient to cause adaptational changes in exercise tolerance related parameters. The results also indicated that some adaptations due to training are rapidly lost over a four week period when horses cease training. Intensity and duration of exercise training may also influence the rate and degree of adaptation to treadmill exercise training. The effect of intensity and duration of training on blood lactate concentrations during and after exercise on a treadmill inclined at 10% was investigated by Evans et al. (1995). Thoroughbred horses were trained at two exercise intensities. One group trained at an intensity that resulted in post-exercise blood lactate concentrations of 4-8 mmol/L. A second group trained at half the speeds of the first group, but twice the distance. Both groups increased fitness, but there was no difference in the changes in fitness between the two groups. However, Thoroughbred horses trained in a fast group (at 80% of VO2 max) had an increase in the ratio of fast twitch, high oxidative fibres, whereas a group trained at only 40% VO2 maxhad no muscle adaptations. Muscle buffering capacity also increased in the fast group (Sinha et al., 1991). These results suggest that training at approximately 80-90% of maximum oxygen uptake stimulates greater adaptation of muscle compared to that found when horses are trained at slow speeds. However, exercise speeds at these high intensities may risk musculoskeletal injury if applied on a racetrack without a period of initial slow speed training.Sprint training Sprint training at or near racing speeds over 400-1600 m or more represents the final phase of training. There are considerable differences the frequency of sprint training between the UK, USA and Australia are in. In the UK, a three day cycle is used by some trainers. Monday and Thursday are trot and canter days, Tuesday and Friday are slow gallop days, and Wednesday and Saturday are fast gallop and racing gallop days. In Australia, two or three fast gallops are generally used each week. A three day cycle is not always possible on Australian racetracks, with restricted access to grass surfaces for the fast work on some days. The sprint training should not be combined with long duration and distances of basic training. If a high volume of base training is combined with sprint training there is a much greater risk of overtraining, resulting in poor food intake, loss of weight, injuries.
In this final phase of race training, it is only necessary for horses to trot and canter approximately 2000-3000 metres on slow days.It is not necessary to monitor heart rate or blood lactate after fast exercise or sprint training in order to specify exact training speeds. All horses will have maximal heart rates (210-230 beats per minute), and have high blood lactate concentrations (15-25 mmol/L) after such exercise. The horse should be allowed to learn how to gallop, pace or trot at high speeds, and then the distance gradually increased. High-speed sprints are only possible over 800 metres. After 800 metres the blood lactate concentrations are near those found after racing, implying that exercise at top speeds is probably unnecessary over distances greater than 800 metres. When a horse is race fit, the training schedule between races can be base training, strenuous training or sprint training.
Base training is used as low intensity training exercise. Strenuous training should be over 1200 to 2000 metres for Thoroughbreds, depending on the distance that the horse is racing. Standardbred trainers tend to use either two one mile heats, with the second heat as the strenuous training. Alternatively, many Standardbred and Thoroughbred trainers combine the strenuous exercise with a final sprint or gallop over400- 600 metres.Most Standardbred trainers in Australia use one fast workout per week between weekly races. However, some Standardbred trainers do not give fast work to some horses between weekly races.
Interval training Interval training refers to use of multiple exercise bouts, separated by rest periods. The recovery period between sessions enables completion of extra exercise, and so the duration of the stimulus is increased. There have been studies comparing the responses to interval training with “conventional training”, but no differences have been reported. However, small differences in performance are difficult to demonstrate in treadmill studies with small numbers of horses. Thoroughbred trainers use interval training routinely, as do many Standardbred trainers in Australia. The only argument against use of intervals is that horse “get too fired up”. and become difficult to control. This is certainly a potential problem because a “fired up” horse will over-race, or “pull”, and waste energy. However, a Standardbred trainer reported that the “gate” speed (acceleration) of a horse was improved by training with multiple 100-200 metre sprints. Several studies have compared responses to interval training. When conventional and interval training of Standardbreds were compared, no significant difference was found in post-exercise heart rates. However the total slow and fast work distances undertaken were the same in both training schedules (Gabel et al., 1983). Interval training over 10 weeks didnot produce greater adaptation in Quarter horses trotting on a treadmill (Rodiek et al., 1987). In a study that compared responses to interval trained and conventionally trained Thoroughbreds in North America no difference was found in heart rate recoveries, run 30times over 1000 metres on an 800 metre track (Harkins and Kammerling, 1990). Limitations of this study included small numbers of horses studied, few measurements of fitness, and use of an 800 metre track for tests of running speeds. It has been shown that Standardbred racehorses interval trained on a treadmill have improved metacarpal bone quality (McCarthy et al., 1988). The training schedule consisted of 5 weeks of slow exercise of 6-12 kilometres/day at 5 m/s. This was followed by a 9 week period of interval training, during the last 3 weeks of which the horses performed 3-4 intervals per day over 600-1000 metres at speeds that resulted in maximum heart rate. Bone quality improved throughout the training period. Interval training may increase the risk of injury (Bayly, 1985). It is therefore very important that the speed of the exercise is closely monitored and is at appropriate speeds, and recovery periods between bouts of exercise are adequate. However, Harkins and Kammerling (1990) interval trained Thoroughbred horses for over 7 months without injury. Figure 11 shows the heart rates during an interval training session used with an elite event horse. Six periods of exercise at a speed generating heart rates of approximately 200 beats per minute were separated by approximately 2 minutes of walking for recovery periods. The horse was exercising at approximately 90% of HRmax (assuming that the maximum heart rate in this horse was 222 beats per min
Skills development Skills development training is designed to increase the ability of a horse to complete a specific task. Important skills include galloping alongside other horses, entering starting stalls and standing sensibly, jumping out of the stalls, and rapid acceleration at the start of the race. Horses also should learn to gallop beside and accelerate around other horses. Horses also need to learn how to gallop on good as well as soft conditions. Pacers need to learn to pace with hopples.
Cross training. Cross training refers to use of exercise that is not specific to the event performed, such as swimming. Training of horses should be specific to the athletic event involved whenever possible. This principle need not be followed rigidly, as there are circumstances when alternative types of exercise may be appropriate for some horses. Non-specific training methods can be used to provide an interesting alternative exercise, and swimming exercise does develop and maintain aerobic fitness. Jumping exercise is also useful cross training for Thoroughbred racehorses. It has been shown that showjumping results in mean post-exercise blood lactate concentrations of 9 + 0.5 mmol/L (Lekeux et al., 1991). These concentrations are similar to those found in Thoroughbred horses exercising at 12-14 m/s. Jumping exercise for racehorses may be a useful adjunct to the usual training routines. It may relieve boredom, and may provide an alternative to high speed exercise as a means of training the anaerobic and muscle buffering capacity.
Swimming is popular with some trainers, and many training centres provide a swimming pool. Horses use a trotting or pacing gait for swimming, and it has been observed that the breathing pattern was characterised by brief inspiration, prolonged expiration, and looked "painful” (Murakami et al., 1976). Certainly many horses appear to have difficulty breathing when swimming.Studies of heart rate during swimming indicate that free swimming is similar in intensity to trotting and slow cantering (Murakami et al., 1976). A training effect was found, as heart rate during swimming decreased over a four week period of regular swimming exercise. Heart rates ranged from 140-180 beats per minute, and blood lactate concentrations only increased by 2-4 fold above resting values during swimming. Horses were exercised for 5 minutes daily in the first week, and the duration was increased by 5 minutes each week thereafter. It was concluded that swimming was appropriate for the development of basic physical fitness and for rehabilitation of horses with limb problems. Prolonged swimming for one hour did not cause excessive increases in body temperature. It was suggested that the direction of swimming in circular pools be changed regularly during prolonged swimming to avoid fatigue in the outside legs.
Treadmill training. Treadmills can be used for base training, and for strenuous training. However, treadmill training ignores development of important skills for racing or competition. Treadmills are not appropriate for sprint training. Treadmills are often used with an incline of 10%. This increases the heart rate, oxygen consumption and blood lactate concentrations (Eaton et al., 1995) because the horse is lifting its mass against gravity as well as moving forward. Treadmill speeds for training usually range from 2-12 m/s (approximately 7-42 kilometres per hour). Gaits at these speeds are walk (2 m/s), trot (3-4 m/s), gallop (greater than 5-6 m/s). At speeds greater than approximately 7-8 m/s (24-28 kilometres per hour) heart rate may be maximal in untrained or partly trained horses. At these speeds it is important to monitor heart rate and blood lactate concentrations after exercise to confirm the training intensity. This procedure should be repeated once per week. Heart rates during and blood lactate concentrations after a standardised treadmill set of exercises will gradually decrease as the horse gains fitness. Treadmill training therefore has the advantage of strict control of training intensity coupled with performance of simple, standardised exercise tests to measure fitness.Another interesting alternative to high speed exercise for strenuous training is treadmill trotting in combination with weight lifting (Gottlieb et al., 1987). Weights were added to a rope that ran over a pulley, connected horizontally from behind the treadmill to a harness. While trotting at 4.8 m/s and lifting loads of 60-100 kg heart rates increased to a mean of 209 beats/min, and blood lactates after exercise ranged from 5-16 mmol/l. The relationships between oxygen consumption and both heart rate and blood lactate concentrations are similar for draught work and normal submaximal treadmill exercise (Gottlieb-Vedi et al., 1991). This technique may be useful for increasing the intensity of the training stimulus at low treadmill speeds. Addition of loads to the sulky has also been used during training of trotting horses in Sweden.A large scale study has studied racing performance of Thoroughbreds in North America with a history of treadmill training (Kobluk et al., 1996). Horses that had been trained on the treadmill for at least 50% of their program for at least 60 days prior to the start of racing were defined as treadmill trained. Racing performance in 107 treadmill-trained horses was compared with results in 214 control horses. In all age groups and classes the treadmill trained horses were equal or superior to the conventionally trained horses. The authors argued that treadmill training also facilitates more efficient quantification of performance.
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