Digging Into Derby Day

The first Saturday in May might be an excuse to indulge in a few mint juleps, but the 1.25-mile Kentucky Derby is a major athletic event. For the 20 horse-and-rider teams, and everyone from owners to trainers, there’s a $2 million purse — and a lot of prestige — on the line. So naturally, experts have dissected nearly every aspect of the race to try to figure out a winning formula.

Some horses love to lead right out of the gate, and others trail first and surge ahead later on, but there’s a benefit to sticking with the pack. A study published in The Royal Society Biology Letters in 2012 analyzed roughly 3,300 races and found that horses that stay back just a bit and let other horses cut their wind resistance, or draft, can decrease their aerodynamic drag by 13 percent. Drafting for 75 percent of the race could conserve enough energy to help the horse finish three to four places higher than horses that don’t draft.

The extreme posture a rider uses, the so-called Martini-glass, helps ensure the horse doesn’t waste extra energy to ferry the pair to the finish line. According to a 2009 Science study, the cramped form uncouples the jockey’s movements from that of their steed and keeps the rider steady. The classic straight-backed posture, on the other hand, requires the horse to move its pilot up and down, which takes a toll on speed. This upright technique was the norm until around the late 19th century, when jockeys who tried the Martini-glass started winning. The switch in stances led to a 5 to 7 percent improvement in race times.

For generations, horse racing’s bread and butter has come down to bloodlines. But now, many experts are looking closely at specific genes, especially the so-called speed gene. Despite its nickname, this gene doesn’t actually indicate how fast a horse runs, but rather how far it likes to run. MSTN, as it’s formally known, encodes for a protein called myostatin, which is involved in muscle growth. Horses that have what’s called a “C/C” variant of this gene are the sprinters, better at running distances of 0.8 mile or less; those with the T/T variant are the marathoners, best suited for running long distances of at least 1.3 miles; and horses with a C/T genotype shine in mid-distance races, like the Derby.

The dirt course at Churchill Downs, where the Derby takes place, is engineered to be as safe as possible for the equestrian elite that thunder around the famous track.

1. 3-inch top layer: Fluffed before every race, it helps decelerate the horses’ hooves as they contact the ground.

2. 5-inch cushion: The heavier particles of the mixture tend to settle here, giving hooves something to dig into as they push off the ground.

3. 8-inch mixture: Rarely disturbed; helps maintain a consistent foundation for the specialized mixture of the upper layers.

4. 12-inch clay base: Supports the upper layers and hasn’t been disturbed for years.

5. 25-foot sub-base (mix of sand and silt): The foundation for all the above layers. It also promotes proper drainage of the track.

The mix of sediments in the track's three layers (Nos. 1-3 above) is, in the words of Goldilocks, just right. The variety in both the sediments themselves and the size of their particles helps ensure a couple of things: that the track isn’t too hard, which would damage the horses’ legs, and that it isn’t too soft, which would mean more work for the racers to propel themselves forward, much like how we struggle to run in dry sand.