Dosage: Pedigree &
Speed in the Thoroughbred
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
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
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.
The last kind of speed we need to discuss is that of instantaneous speed or, more realistically, fractional speed and pace. If one wishes to talk about the truly fastest horses, then there are a host of runners capable of getting the first quarter in :21 and a fraction or even less. But in actual fact, these types most often show their speed for only a brief time in the early stages of a race, usually tiring dramatically well before the finish. Often we call this "cheap speed". It is only cheap because it is not expressed over the full distance of a race. Actually it is not cheap at all. It is as valid a physiological expression as any other kind of speed. It just so happens that it occurs at one extreme of the speed frontier and well outside our normal frame of reference for meaningful racing. We view these runners in the same way we view runners that hold records at the other end of the spectrum, say 3 miles. In the end, we are drawn to speed displayed at distances that we, as a society, choose to race our horses. Within these bounds, all record holders are essentially equally fast.