What Defines a Kentucky Derby Champion? A Big Heart, Powerful Lungs, and Strong Legs

Horses have honed their abilities, such as running, jumping, and pulling, as humans have bred and trained them for various purposes over thousands of years. The 151st Derby, the most-watched horse racing event, not only highlights the skills of these animals but also raises concerns about their treatment and well-being. Advocates have long voiced worries about injuries and fatalities, especially after twelve horses died at Churchill Downs two years ago.

There’s no doubt that the relationships between humans and horses have transformed warfare, agriculture, and society.

Timothy Winegard, a historian at Colorado Mesa University and author of the recent book, The Horse, remarked, “We’ve combined our intellect with the horse’s size, strength, stamina, and speed to create the most unstoppable animal coalition.”

Why Are Horses So Powerful?

The horse’s heart and lungs contribute significantly to its remarkable power.

Hearts typically weigh between 10-12 pounds (4.5-5.4 kg), roughly 1% of the horse’s body weight, compared to about 0.5% for a typical human heart. The famous horse Secretariat, who won the Triple Crown in 1973, was later found to have a heart weighing over 20 pounds (9.1 kg).

A horse’s heart is designed for exercise, with a resting heart rate around 34 beats per minute that can rise to 220 or 240 during a race—much faster than a human’s maximum during intense exertion.

“One unique aspect of horses is their incredible capacity to circulate blood throughout their bodies. They can achieve high heart rates while remaining safe,” explained Sarah Reed, a researcher at the University of Connecticut.

Additionally, horses possess a lung capacity of 60 liters, ten times that of a human.

“This extensive lung capacity allows oxygen to efficiently transfer from the air to the blood, which is essential for sustaining aerobic energy,” noted Farmer.

Recent research published in the journal Science indicates that genetic mutations enable horses to mitigate the adverse effects associated with ultra-high energy production.

“Horses are exceptional athletes because they can deliver significantly more oxygen to their muscles than elite Olympic athletes. They have larger energy reserves and more efficient systems…and these mutations play a role in both aspects.”

What Contributes to a Horse’s Speed and Skills?

Various biological characteristics enhance a horse’s abilities.

Horses store excess red blood cells in their spleens, which are released to enhance oxygen transport during intense exertion.

“During exercise, adrenaline triggers the spleen to circulate these excess red blood cells,” said veterinarian Hillary Clayton. “Essentially, what a horse accomplishes is a form of ‘natural blood doping.’”

Furthermore, a horse’s brain is adept at processing sensory information and reacting swiftly. Although their frontal lobe—the section associated with thinking and planning—is proportionally smaller than that of humans, horses are hardwired for play and independent running without fear, as explained by Dr. Scott Bailey, a veterinarian at Clayborne Farm. This focus is critical for athletic performance.

The bone structure and muscle makeup are also advantageous. The ligaments and tendons in their hind legs function like springs, and as Farmer noted, like other large prey animals, they possess “long, slender legs designed for running.”

What Are the Risks for Horses?

Adjustments that enhance a horse’s speed also increase the risk of injuries. Their slender legs endure the impact of each stride, and over time, repetitive stress during racing and training can lead to tendon and ligament damage, Reed stated.

In 2023, fatalities occurred not only at Churchill Downs but also at other major racecourses, affecting public perceptions of the sport and prompting changes. No specific cause of death was identified. However, in 2024, Churchill Downs improved the equipment used on its racing surfaces and added a veterinarian dedicated to horse safety and integrity.