Speed in the Thoroughbred 

Speed is perhaps the most mysterious concept in all of Thoroughbred racing. For example, ask friends which racehorse was the fastest in history and you're likely to get a host of answers. Was it Secretariat, Citation, Dr. Fager, Ruffian, Man o' War? Unfortunately, unless everyone is using the same definition of speed there is no useful basis for discussion. The only thing most people will agree to is that speed, whatever it is, is very important.

As a prelude to our discussion, let's take a look at the speed records for North American dirt races at the most common distances through 2005. Table 1 lists the final record times between six and twelve furlongs.

The oldest of these records is that of Dr. Fager at a mile set in 1968 and matched by Najran in 2003; the newest is G Malleah’s six-furlong record set in 1995. If we plot the distance against the record times and subject the individual data points to linear regression we find something interesting.

Linear regression creates the best straight line that can be derived from the individual data points. Sometimes the data points can be far away from the newly created line. In such a case the fit of the data points to the line is not very good and the relationship, here between time and distance, would be poor. But, in fact, when record times are plotted against distance, the correlation is outstanding to the extent that no record is more than 0.20 seconds away from the time predicted by the line. The calculated correlation coefficient (a mathematical measure of how close the points fit the generated line) is 0.99995 where a maximum value of 1.00000 indicates that each data point fits squarely on the line. These comparisons are shown in Table 2.  

The actual record times falling very close to a straight line defines a specific relationship between the time at one distance and the time at any other distance. In this case the relationship is expressed mathematically as: Time = (12.89 x Distance) – 10.90. This relationship between time and distance describes the current state of physiological development of the Thoroughbred with regard to speed. The line represents the frontier of speed in the Thoroughbred, the ultimate expression of directed breeding for well over 200 years. In the future, these records will be broken, one by one, and a new line (or frontier) will be established as the breed evolves toward even greater speed. The linear relationship between time and distance is an ongoing phenomenon and can be demonstrated at any point in the past. For example, Tables 3 and 4 display the equivalent data found in Tables 1 and 2, but through 1976. Here the calculated correlation coefficient is a virtually identical 0.99997.  The largest difference between the actual and predicted time is 0.40 seconds for Dr. Fager's mile record. It is interesting that the actual time was 0.40 seconds FASTER than the predicted time. Since this has also been the longest standing record, it suggests that Dr. Fager stepped well beyond the established speed frontier in his record-setting effort, so far, in fact, that the record remains intact after 36 years.

Any shift of the straight-line plot on a graph over time is simply a visualization of the movement of the frontier of speed. Consequently, it is fair to say, because of the linearity of the time-distance relationship, that all of the record holders were equally fast in the context of the distance at which they set their record. That no single horse is likely ever to hold the record for both six and twelve furlongs is the result of variation in type, although obviously the record holders at both ends of the spectrum are ultimately part of the same gene pool. They differ by some degree in such things as biomechanical efficiency and/or cardiovascular characteristics. These factors then position their optimum performance traits at different regions of the speed frontier. But in reality they have run as fast as a Thoroughbred can run up to this point at a given distance.

Now we can look at speed from a different perspective. Table 5 displays the records at the various distances in terms of the average speed in seconds per furlong over the distance of the record-setting race.

The gradual decrease in average speed at each succeeding longer distance is clear. In no case has a record holder at a given distance maintained the same speed as was achieved by a record holder at the next shorter distance. On this basis the fastest horse in history on dirt between six and twelve furlongs has been G Malleah. Tell that to your friends and they will begin to question your sanity. But in fact, on an absolute basis, and ignoring the notion of fractional speeds which we will address later, G Malleah ran faster than any horse we have ever seen at these distances over the course of an entire race. If he were able to sustain that rate of speed over a mile and a half he would have beaten Secretariat in the Belmont Stakes by over 50 lengths. What do you suppose a horse like that would be worth? And here again is the key to understanding speed in the racehorse. It is not merely the rate at which the horse moves around the track; it is related to how long he can sustain that rate. As before, the concept of speed in racehorses has meaning only in the context of the distance involved because the breed is constrained by the present state of evolution and the resulting limits of physiology. It is not physically possible to run the same all out speed at every distance. If all races were contested at six furlongs, then Secretariat and Spectacular Bid would be considered slow because their expression of speed would not be apparent in a short sprint. On the other hand, if all races were run at twelve furlongs, then G Malleah, Rich Cream and Time to Explode would probably trail the field under the wire because they would not be able to sustain their best pace over the entire mile and a half. This bears on the high esteem accorded brilliant milers, particularly as breeding animals. Whether we recognize it or not, highlighting the exploits of milers merely ascribes some versatility to a runner which can show near sprint-like speed beyond a pure sprint distance. In fact, milers are no different than any other runners in physiological suitability. They also fit the continuum of the time-distance relationship. Rather, we are placing a value on ability at a distance which essentially represents the average, neither sprint nor route. Frankly, there is no virtue in that view. Great sires can and do come from all distance categories whether it be sprint (e.g., Mr. Prospector), mile (e.g., Fappiano) or route (e.g., Nijinsky II). Most likely, our affection for brilliance is a consequence of our perception of racing opportunity for the foals. As races become shorter and the pressure for early maturity increases, there will be a "natural selection" for sires thought to be capable of transmitting desired traits of speed and precocity.