Men are faster than women. but does that mean bets should always be placed on colts?

August 26, 2002

San Diego, Calif. -Was Lassie only the second fastest collie in the valley? Was Roy Rogers's horse Trigger faster than Dale Evans's filly, Buttermilk? Men are readily acknowledged as faster runners than women. Can the same assumption be made about gender in horses and dogs?

Background
It's not too hard to see why that assumption might be made. Sir Roger Bannister ran the first sub-four minute mile in 1954. Forty-eight years later, the men's record for the mile is 3:43.13; a Russian woman holds the corresponding record for women at 4:12.56. Those who organize competitive track and field events realize that although a given individual woman may be faster than a given individual man, this gender difference is apparent at levels from amateur to elite.

Competitive racing standards are more egalitarian in the animal kingdom. Thoroughbred (flat racing) and Standardbred (harness racing) horse races are generally divided by gender. However, female horses (fillies) have been outright winners of some premier events such as the Kentucky Derby, Breeder's Cup races, and the Hambletonian trotting race. Considering that fillies do enter the winner's circle, a researcher wondered if a consistent gender difference in running performance does exist in horses, and if so how the magnitude of that difference compares to that seen in humans. The investigation also extended to an examination of a gender difference in running speed of the dog, another competition species. Unlike human and horse races, Greyhound races are not segregated by gender, suggesting that these dog owners do not perceive a gender difference in running ability.

In male and female running ability, it is appropriate to ask if there are physiological parameters known to affect athletic ability. In humans and animals, maximal aerobic capacity, the maximum rate at which the body can use oxygen to produce energy, is often used as an index of endurance running ability. This index is significantly greater in men than women, even when body mass is taken into account. The higher maximum aerobic capacity of men vs. women has been verified repeatedly, in young and old, athletic and sedentary. The differences between the sexes that underlie men's athletic advantage include body composition (percent body fat versus lean body mass), cardiac size, blood volume, and hemoglobin concentration. For a given total body weight, men have more lean body mass and less fat. Men also have larger hearts and a greater maximum cardiac output (liters of blood/minute) then women.

A sexual dimorphism does occur in both horses and dogs in terms of overall size - males are generally taller and heavier than females. Body composition is seldom measured in these species, although subjectively most horsemen feel that stallions are more muscular than mares. Gender-based comparisons of heart size, blood volume, and hemoglobin concentration have not been published for these species. Furthermore, the factors that limit maximum aerobic capacity in the horse appear to be associated with the lung, rather than with the cardiovascular system as in humans. Thus, evidence to support a gender difference in maximum aerobic capacity in horses and dogs is lacking, primarily because the possibility of a gender difference in oxygen consumption of horses or dogs has never been systematically investigated. Nevertheless, female horses are rarely run against males.

The Study
The author of "Gender Difference In Running Speed: Humans Versus Horses And Dogs," is Pauline Entin, PhD, Assistant Professor, Department of Exercise Science, Northern Arizona University, Flagstaff, Az. Dr. Entin will present her findings at the upcoming scientific meeting, "The Power of Comparative Physiology: Evolution, Integration and Application." The meeting, being sponsored by the American Physiological Society (APS), is being held August 24-28, 2002, at the Town & Country Hotel, San Diego, CA. Further information about the conference is available at: http://www.the-aps.org/meetings/aps/san_diego/home.htm

This study sought an empirical answer to the question of a gender difference in running performance in horses and dogs by comparing actual racing velocities. Given the observation that horse races, both flat racing and harness racing, are segregated by gender whereas Greyhound races are not, the research hypothesized that a difference between the sexes would occur in horses but not dogs.

Methodology
Data on horse and dog running speeds were obtained from several different on-line sources.

Results
Regression analysis of actual race data revealed a small but significant effect of gender on the racing velocities of Thoroughbred horses and Standardbred pacers, but not Standardbred trotters or dogs. It is notable that in all cases males held a slight advantage over females, although this difference was not significant for the trotters and dogs. When compared to the approximately 10 percent gender gap in peak running speeds of humans, the difference in the animals was small - no greater than 1.2 percent.

The relatively small difference between the genders in both horses and dogs agrees with the lack of evidence of relevant physiological dimorphism in both species. Although the difference in the horses was significant, the one percent gender gap could be explained by training methods or psychological factors as well as physiological attributes. It is a widely held belief among racehorse trainers that female horses should not be trained as hard as male horses, and trainers are loathe to enter female horses in races that are also open to males. Greyhound races are not segregated, presumably signifying that Greyhound owners and trainers believe that females can compete successfully with males.

Conclusions
Given the evolution of the horse as a prey species and the ancestors of the dog as a predatory species, both dependent on running, it is tempting to speculate that natural selection operated on the running ability of both males and females of these species. In contrast, archeological evidence suggests that human ancestors were tool users and may have had gender-specific tasks at least as much as one million years ago, possibly lessening the importance of running speed particularly in females. This analysis is strictly speculative, yet it is clear that humans have selectively bred both racehorses and Greyhounds for speed in both genders for several hundred years, whereas humans do not select their own mates based solely on running ability.

In conclusion, although male horses and dogs do hold a slight speed advantage over conspecific females, the difference is an order of magnitude smaller than that seen in humans (one percent versus 10 percent). Factors other than physiological differences may explain why horse races are traditionally segregated by gender.
-end-
The American Physiological Society (APS) is one of the world's most prestigious organizations for physiological scientists. These researchers specialize in understanding the processes and functions by which animals live, and ultimately underlie human health and disease. Founded in 1887 the Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals each year.

Contact: Donna Krupa
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