Last month, this column covered some of  the basics in developing a physical conditioning program (see "Getting Your Horse in Shape" in the February 2002 issue of The Horse, article Quick Find #3263 at The early phases of training, often termed "legging-up," are designed to provide a foundation of fitness and musculoskeletal strengthening that better allows the horse to handle the rigors of training and competition. Beyond this foundation, training must be specific to the intended athletic event to ensure that the body is fully adapted or "tuned" for this activity. It almost goes without saying that the physiologic demands for Thoroughbred or Standardbred racing, eventing, reining, barrel racing, show jumping, or endurance racing are all very different, so it makes sense that no one conditioning recipe can be applied to all of these disciplines.

However, regardless of discipline, all conditioning programs share one important goal: To improve the horse's capacity to provide energy to contracting muscles. That means he can increase the speed and efficiency of his fuel use (in a sense, get better gas mileage).

A second common goal is to improve biomechanical efficiency and skill level. This aspect of training is much more sport-specific and won't be discussed here. Instead, we will focus on the principles behind two conditioning methods called interval training and hill work, which are geared toward attaining peak cardiovascular fitness, muscular strength, and efficiency of fuel use during exercise.

Training Methods

By and large, all conditioning programs have two basic elements: (1) the foundation phase, and (2) more intensive training that brings the horse to peak fitness and readiness for competition. For completely untrained horses or those coming back from a lengthy lay-up (greater than three to four months), the foundation phase might last 12-16 weeks, with a gradual increase in training load during this period. Foundation training is typically low-intensity and done in a continuous manner, i.e., each workout is a single bout of exercise, including warm-up and cool down.

After completion of the legging-up phase, the horse needs more intensive, higher "quality" conditioning. Typically, this will involve an increase in the duration of exercise bouts, an increase in intensity, or both. For the short distance expert, such as a barrel-racing horse, the emphasis should be on high-speed work,  whereas the endurance athlete needs some distance work to improve stamina.

What's debated is whether to stick with a continuous style of training, or to mix it up a little by asking the horse to perform some type of intermittent or interval training. Interval training involves multiple bouts or heats of strenuous exercise separated by relatively short recovery periods. Some traditionalists, particularly in the world of Thoroughbred racing, prefer to stay the course with continuous-type training, although the intensity will certainly be increased relative to early training. Most days the horse will perform lower-intensity work with a lot of trot and canter work and, every four to five days, a more strenuous workout will be completed (for example, a three- to five-furlong gallop at near-maximal speed). Some view this relatively light conditioning schedule as inadequate preparation, but the fact remains that many Thoroughbreds have raced successfully on such programs.

For human runners, whether they are sprinters, middle-distance athletes, or marathoners, interval training is an important part of the conditioning program and is believed to be crucial for development of fatigue resistance and improved running speed. In the equine world, interval training has been popularized by Tom Ivers, president of Equine Racing Systems, Inc., and the author of The Fit Racehorse and The Fit Racehorse II. His methods certainly have a following, particularly among Standardbred and Thoroughbred trainers.

Explains Ivers, "Interval training allows for more event-specific work to be accomplished by the horse without the risk of fatigue and subsequent injury."

Interval training is not just for racehorses, though. Even endurance horses can benefit from this method. There is evidence that this form of training promotes optimal strengthening of the musculoskeletal system, improving the horse's ability to withstand the rigors of a competitive campaign. Ironically, though, one of the potential pitfalls with interval training is musculoskeletal injury. The keys to preventing such problems are a thorough foundation conditioning program and avoidance of the temptation to push too hard, too soon, once interval training is started. Always remember that the skeleton and other supporting structures are much slower to adapt to the rigors of training compared to the heart and muscles.

The incomplete recovery with interval training means that subsequent bouts become progressively harder. The latter repetitions might be completed at a faster clip than the first one or two. However, the idea is not to run all-out to fatigue during the repetitions, as this inevitably leads to injury.

Another type of intermittent training is "fartlek," a technique first used by Northern European endurance athletes. Literally meaning speed play, fartlek involves repeats of fast canter or gallop work interspersed with recovery periods. However, in contrast to true interval training, the horse is normally allowed a complete recovery before starting the next hard bout (more on the recovery aspect later). This technique is popular among three-day event and steeplechase riders and trainers, and works best in large, unfenced fields or similar wide-open spaces that give the horse and rider plenty of scope.

A further twist on this theme is to use uphill intervals. The runners among you will fully appreciate the virtues of regular hill work--peak fitness can be achieved a good deal faster compared to a training program done mostly on level terrain. This means fewer miles, less time, and less wear and tear on the legs. Human athletic trainers routinely prescribe "hill repeats," usually involving six to eight bouts of running up a moderate slope for 50-60 seconds with a jog recovery to the base of the hill between bouts. These same principles can be applied to the conditioning of horses.

Energy Systems

To appreciate the benefits of these intermittent training methods, we need a brief review of energy use during exercise. Adenosine triphosphate (ATP) is the body's energy currency, and it drives muscle contraction. The horse's muscle tissue contains very small amounts of ATP as well as another high-energy fuel called creatine phosphate (CP), which can be used to replenish ATP. However, these stores of ATP and CP can support only a few seconds of intense muscular activity before the body must draw upon other fuel reserves to replenish the supply of ATP.

During exercise, ATP can be replenished by aerobic (with oxygen) and anaerobic (without oxygen) metabolism. The two major fuels used are glucose (from glycogen) and fat. The main distinction is that glycogen can be burned both by anaerobic and aerobic metabolism, whereas fat can only be used aerobically. The relative contribution from these two processes mostly depends on the intensity of exercise. Trot and canter work is almost entirely aerobic, whereas a full gallop will require use of considerable anaerobic energy (i.e., only from glycogen).

Another important distinction is the efficiency of these two processes. When fat and glycogen are metabolized aerobically, a large amount of ATP is produced without the accumulation of waste products that could negatively affect muscle function. On the other hand, anaerobic metabolism is quite inefficient--only a small amount of ATP is produced and lactic acid, the end-product of this process, accumulates in muscle. And it is  known that too much lactic acid is one factor that contributes to fatigue.

Still, use of the anaerobic system has two advantages. First, the ATP is generated much more quickly compared to aerobic metabolism. Second, when a horse reaches his maximum rate of oxygen consumption during hard exercise, the energy for any further increase in speed or effort can only come from anaerobic metabolism. And, to a degree, the horse's ability to run fast (and maintain that speed) depends on his anaerobic capacity--the amount of energy that can be generated from this system.

Although somewhat controversial among exercise physiologists, it has been suggested that intermittent or interval training methods have at least two major advantages over more conventional horse conditioning programs. First, they can promote a more rapid increase in maximum aerobic capacity. So, after training at any given running speed, the horse will be working at higher metabolic efficiency--effectively getting better "gas mileage."

Second, there is evidence of an increase in anaerobic capacity, probably through adaptations in the fast-twitch muscle fibers. These fibers also might become more resistant to the fatiguing effects of lactic acid and other by-products that  accumulate during intense exercise. Repeated bouts of high-speed running also might improve the horse's coordination and biomechanical efficiency. Added up, these adaptations should improve stamina and perhaps speed.

Getting Started

The cardinal rules with intermittent training protocols are to ease in gradually and to work with a plan. As well, you need to use a heart rate (HR) meter to monitor the horse's physical response and to determine the length of the "partial recovery" periods. Before starting, you must plan the distance and speed of intervals, the number of repeats, and the duration of recovery periods. Start conservatively and build from there. For example, an event horse might start with two or three canter intervals at 0.4-0.6 miles (600-800 meters) per minute with three-minute intervals between the canters. Over a four to six week period the number of intervals can be slowly increased (no more than one every two weeks). An alternative approach is to target a particular range in heart rate during the intervals (e.g., 190-200 beats per minute). Also recognize that done properly, interval training requires a greater time commitment compared to more conventional, contin   uous conditioning sessions.

Perhaps most importantly, a thorough musculoskeletal examination by your veterinarian is recommended before launch ing into this type of training. Subtle injuries must first be resolved. On the days that interval training is to be used, the horse should be closely evaluated before the workout. Inspect his legs and observe him at the walk and trot. This examination needs to be repeated after the workout sessions.

Ivers recommends starting with a total distance of about one-half of the normal daily work. For example, for a horse which normally completes two continuous miles of canter/gallop exercise, a mile interval workout is a reasonable starting point (after a thorough warm-up). The first interval session should be run slightly faster than the speed used during continuous training. The recovery periods should be active, with the horse walked or jogged to promote clearance of lactate and other waste products from muscle. As a general guide, start with only one interval session per week and never use more than two weekly interval sessions.

The recovery period will vary in length (e.g., initially they might be four to five minutes long, eventually decreasing to two to three minutes) depending on the speed and duration of the actual interval. The heart rate response will serve as the best guide. Target heart rate during the hard intervals might be 190-200 beats per minute, with recovery heart rate in the 110-120 beats per minute range. The recovery should not be complete, hence the need to keep the horse moving. Early on, the horse might walk during recoveries, then as he becomes fitter and more accustomed to interval training, the recoveries will consist of trotting exercise. One criterion is to not start the next interval until the heart rate falls below 110 beats per minute. However, the timing of this response also needs to be considered--failure of the heart rate to fall below 110 beats per minute by 10 minutes post-interval training (with the horse at the walk) probably indicates fatigue and the need to end the training session. The heart rate response (increase) during the intervals should also be monitored. As training progresses, heart rate at a given speed should decrease, indicating improving fitness.

As the horse's fitness level improves and he becomes accustomed to the routine, the intensity and number of repetitions can be increased, and the length of the partial recoveries shortened to increase the overall training stimulus. Ivers' preference is to see a progression from longer, slower intervals to faster, shorter heats.

For Non-Racing Horses

For disciplines not demanding high speed, the principles of interval or fartlek training can still be used. A show jumper might complete two-minute intervals at a steady canter (13-15 mph or 21-24 km/ hour) that is similar to the pace used in competition. For the eventer, a sample workout might include three-minute canters at 500 meters/minute (a heart rate of 180 to 190 beats/minute should be attained) with four to five minute periods of active rest. Over a period of weeks, the speed and length of the intervals can be increased (e.g., seven to eight minutes at 21-22 mph or 33-35 km/hour) with shorter recoveries (two to three minutes). Endurance horses might complete something similar, with canter work both on level terrain and up hills.

Hill Training

Use of hill intervals is ideal for strength training of eventers, endurance horses, and show jumpers. The drive required to propel the horse uphill promotes muscle development in the hind legs and, for the eventer and endurance horse, is important preparation for the terrain to be encountered in competition. As with interval training on level terrain, start slowly and build from there.

Some slow uphill work (walk and trot) is good general strengthening exercise, while faster hill work will improve cardiovascular fitness and build explosive power. For horses required to compete on hilly terrain, it is also important to practice some downhill running. Hills with a four- to 10-degree grade are suitable for incline  work.

Be cautious on hot and humid days. With interval and hill work, the overall exercise intensity is much greater compared to more routine conditioning, so more heat will be generated in muscles and the horse will lose substantial body fluid via sweating. Postpone interval or hill sessions on hot days or, at the minimum, reduce the intensity and number of repeats for that day.

Choice of underfoot conditions is also important--avoid deep, sandy, or rocky terrain. A firm but slightly yielding surface is best.

Interval training and hill training are not for everyone, or every horse. The time commitment alone might make it difficult for you to utilize these methods. However, when done correctly, these forms of training are certainly one way to ensure that your horse reaches peak fitness and performance.

About the Author

Ray Geor, BVSc, PhD, Dipl. ACVIM

Ray Geor, BVSc, PhD, Dipl. ACVIM, is professor and chairperson of Large Animal Clinical Sciences at the College of Veterinary Medicine at Michigan State University

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