The Thoroughbred's cardiovascular system is dynamic and fragile, but it can be molded by exerciseThe Thoroughbred's cardiovascular system is dynamic and fragile. A resting heart rate of under 40 beats per minute can soar as high as 240 during a race, while the red blood cell concentration can double through splenic contraction. Huge fluid shifts take place, shunting oxygen-rich blood from the gut and internal organs outward to the working muscles. A special muscle cell, the fast-twitch high oxidative cell, enables the animal to sustain speed that would quickly paralyze its natural predators with lactate fatigue. Compared to a human's, the Thoroughbred's cardiovascular system is a miracle of coordinated efficiency.
But most Thoroughbreds bleed from the lungs during a race. And many Thoroughbreds are incapable of maintaining a high percentage of their inbred speed for longer than one minute. Somehow, our sport has humbled a superb natural design and scientists have yet to determine the underlying causes. Gone are the days when a Thoroughbred like American Eclipse could deliver three four-mile match races on a Sunday afternoon, best two out of three, all miles faster than two minutes. Year by year, many of our championship races are being shortened because fewer and fewer horses can make the distance. At some tracks in America, a mile is considered a marathon.
Some say it's the breeders' fault, that breeders are mating for speed instead of staying power. If your perspective is just Thoroughbred racing, this argument can seem logical-except to the breeders, some of the best of whom tell me that the goals of their matchmaking remain the same as they've always been: a racehorse with the versatility to win at classic distances. From an exercise physiologist's viewpoint, the argument is illogical, because most human middle-distance (half-mile and mile) world records are being set by stretched-out sprinters. Coaches of human athletes are delighted with speed in their athletes because they are sure they can design a conditioning regime which will allow their athletes to maintain speed for longer than two minutes.
Like virtually all the systems of the athlete's body, the cardiovascular system is "plastic"-you can change it. Unlike muscle, though, and more like the structural components, the cardiovascular system requires time and progressively increasing stimuli in order to adapt. That's because tissues are being changed, not just chemicals. Conditioning can cause the heart muscle to expand its capacity and power. Increased cardiovascular fitness means an expanded capillary bed in the musculature and at the heart/lung interface. Major and minor blood vessels strengthen and become more capacious. The autonomic nervous system becomes attuned to high intensity effort and its response time quickens, spinning up the heart rate more quickly while minimizing overshoot. The autonomic nervous system learns to shunt blood to the working muscles more quickly.
Meanwhile, the horse's spleen increases its capacity for sequestering red blood cells. As the horse becomes fitter, the PCV count will drop into the low 30s due to the increased capacity of the spleen-this is not a sign of anemia, but of fitness. The viscosity of the blood will drop so that the vital fluid can pass though blood vessels more rapidly. The total volume of the blood will increase. At the local muscle level, oxygen uptake will increase because of the presence of many more mitochondria. Oxidative enzymes are stored away in larger quantities.
All of these changes, and many more, are designed to deliver more oxygen to the working muscle cells, staving off fatigue and enabling the athlete to carry a higher percentage of his speed farther. In the Thoroughbred, the changes, when they occur, are man-made. The breeders have nothing to do with it. The Thoroughbred racehorse, unfortunately, is a creature of his trainer's habits, and trainers' habits, in this author's opinion, have been regressing over the past few decades.

Building a better beast
How do you build a stronger cardiovascular system in the Thoroughbred? How can you build a vasculature that will not explode under the pressure of 240 heartbeats a minute and double-thick blood? How can you put staying power into an animal with overwhelming natural speed? It's a matter of obeying the prime law of conditioning: the Law of Specificity. Show the body what you want, and it will remodel itself to better conform to your demands. In this case, we are looking for sustained high heart rates.
Colin Hayes, who was until his retirement Australia's premier Thoroughbred trainer at classic distances, has a three-quarter-mile uphill gallop that he shoots three times in a single workout. Johnny Tammarro tells me Max Hirsch used to throw a couple of mile breezes at his horses on a single day, and Johnny has done it himself. D. Wayne Lukas likes strong two-mile gallops every day. The handlers of Risen Star found that longer strong gallops delivered a better classic racehorse. Stanerra won the Japan Cup coming off 15-mile galloping days. I believe that Charlie Whittingham and Jim Day spend significant time with longer, slower workouts. Many European trainers use long, strong gallops or multiple heats to produce their classic winners. Image of Greatness, Saratoga Passage, Sapient, Bagatelle, The Very One, and a number of other top horses were built with higher mileage and multiple heats of work on a single day. In New Zealand, the good horse Jondolar delivered a 1:33 mile coming off six-mile days, triple one-mile heat work, triple three-quarter heats, and double five-eighths breezes. Argentinian horses often train with ladder workouts: one mile, followed by three-quarters, followed by five-eighths, followed by a half-all in one session.
All of these approaches contain a common thread-high heart rates sustained over longer than normal periods of time. Not maximal heart rates, which will occur in a fast three-eighths breeze, but heart rates that exceed 200 nevertheless. Sustaining such heart rates over a stretched-out period of time means that lactic acid will accumulate, triggering requests to the cardiovascular system for more oxygen. As these demands are met, more requests come in, eventually overwhelming the delivery system and sending the lactic acid curve into a parabolic leap. The body remembers this challenge and, during subsequent days of recovery, strengthens the entire delivery system. Step by step, as the working challenge is progressively loaded, the body keeps on responding by continually strengthening the heart, lungs, and vasculature.

Walking a tightrope
There are two problems here. The first is that you're walking a tightrope between exercise that will benefit the animal and that which will produce so much fatigue that his stride will deteriorate, producing injury instead of fitness. The second problem is that if you're going to approach this kind of work in a safe, effective way, you have to take time-a lot of time-to build to a volume and intensity of work that will make the key difference.
The solution to the first problem is heart rate monitoring. With an on-board heart rate monitor, heart rate responses and recoveries can be read, computerized, and graphed. For example, if a given mile work produces a 212 peak heart rate and a recovery of 97, then you can increase either the distance or the intensity of the exercise safely. On the other hand, a 216 peak with a 135 recovery indicates that you are right on the ragged edge of fatigue with this animal and had better stay right where you are until the body has a chance to adapt.
There is no solution to the problem of the necessary extra preparation time for superior cardiovascular development. Worse, you cannot go back for it once you are racing and find you have a "short" horse. You have to make your investment right in the middle of training, before you have "taken a peek" at your horse's speed. But I can give you a good idea where your maximum benefit per day-rate investment is going to occur: four-mile days.
Over the past decade, hundreds of Thoroughbreds have been trained to mileage bases of four, six, eight, and 15 continuous miles on a given day. While higher mileage horses have generally done better than the lower mileage animals, there is good and massive evidence that a four-continuous-mile workout delivers the most observable performance increase per extra mile. In other words, a four-mile horse is much better off than a two-mile horse and a six-mile horse observably fitter than a four-mile horse. A four-mile horse can easily accommodate a 2 X 1-mile workout, as long as the speed of these workouts is brought on gradually. These "doubles" will dramatically build the cardiovascular system.
That this approach seems radical, even crazy, is a comment not on my own sanity, but on today's lack of innovation in training modalities. It is a comment on the constraints of attempting to condition athletes at the racetrack, where the track closes to training early in the morning and the exercise riders charge $5-to-$7 for "once around." Essentially, trainers are correct when they say that "it can't be done" on the racetrack. But it has been done on the racetrack.
In Lexington, Leonie Ommundson is delivering this kind of exercise via high speed treadmill, and has produced a number of winners already. Here in Washington, we have two high speed treadmills with 40 Thoroughbreds performing precisely controlled and monitored exercises-I will let you know how it turns out.
There are several high speed treadmills around the country helping to produce winners at all distances, and this just might be the training technology of the future. The big advantages are controlled, monitorable, cost-efficient, and race-specific exercise, night or day, rain or shine. You can buy half a dozen high speed treadmills for the cost of building one cheap racetrack. You can exercise a dozen horses for the cost of one "once around" ride.
No matter how you get it accomplished, cardiovascular development is money in the bank, especially at classic distances. An extra advantage is that, while you are building heart and lungs, you are also building structural fitness, coordination, intelligence, good behavior, and a deep sense of well-being in the horse. You will get your riders fit, too.
One final reminder: a horse that breaks out of the gate and sprints a quarter before getting caught has an advantage over most of the horses in the gate-his splenic contraction has doubled his red cell count. As far as his cardiovascular system is concerned, he is at least three-sixteenths ahead of any horse which has not experienced the adrenaline charge that contracts the spleen. Turn your horse loose for an eighth or a quarter while backtracking the far turn after the post parade to take early advantage of this backpack of endurance.
Tell the stewards Ivers told you to do it.