Update: On June 6, 2015, American Pharoah won the Belmont Stakes and took the Triple Crown.

California Chrome had it all. The three-year-old thoroughbred won the Kentucky Derby last year. Two weeks later, he topped the field at the Preakness, becoming the only horse bred in the Golden State to ever win both races. Then, on June 7, 2014, he was about to run the Belmont Stakes, the final race in the so-called Triple Crown. The last horse to win all three of these races was Affirmed in 1978, but maybe Chrome had a chance to bring the title into the 21st century: The colt had a prime starting position, second in the gate. The odds were on his side, at 3-5. His legion of fans, the #Chromies, mustered on Twitter.

But Chrome fell short. Tying for fourth, he became the 13th horse to win the first two legs of the Triple Crown only to fail in the third in almost 40 years. The winner at Belmont, Tonalist, hadn't raced in the Derby or the Preakness, and in a post-race interview, Chrome's co-owner Steve Coburn argued that the Triple Crown should be a closed circuit: No parachuting in to run the Belmont if you haven’t already run the previous races in the series. "It's not fair to the horses that have been in the game since day one," Coburn said. "It's all or nothing. This is the coward's way out."

Coburn has a point. Post-race recovery is no joke for a thousand-pound animal that can run more than 40 miles per hour. There are two weeks between the Derby and the Preakness, and three weeks between the Preakness and the Belmont. That tight schedule—and the super-specific needs of racehorses—means horses competing in the grueling back-to-back-to-back Triple Crown races have a big disadvantage against fresh horses.

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This Saturday, another horse will face the same challenge that Chrome did. American Pharoah won the Derby. He won the Preakness. Now, he'll have a shot at claiming the biggest title in racing (with the same jockey who rode Chrome, no less). But he will be competing against several horses that skipped earlier races—and dealing with the physiology and biochemistry involved in equine race recovery.

Keeping the Fuel Tank Topped Up

During high-intensity exercise, humans and other animals need a lot of energy. We store it in the muscles and liver as glycogen, a type of sugar that the body can easily burn for energy. Ever been struck, suddenly, with fatigue during a race or other exercise? That's your body running out of glycogen and switching to another, less easily metabolized source of energy: fat. Clair Thunes, a horse nutrition expert who teaches at UC Davis, recalls showing students a race where a horse held second place until the last turn. "He comes into the stretch and suddenly starts going backward and backward, the green of the jockey's silks falling back through the field until it trails off in the finish," she says. "To me, it looked like the horse hit a wall."

Distance runners, cyclists, and other human athletes can refuel during long bouts of exercise with sports drinks and energy gels. But racehorses can't exactly down a shot of Gu during a 2-minute race. They have no time (and no thumbs). And trying to top a horse up before a race by feeding it what's known as glycogen loading paste wouldn't help much either. A healthy horse's stores will already be full-up.

As the animal blows through its glycogen, something else happens: Its muscles produce lactic acid. The enzymes that break glycogen into glucose that the body can metabolize are sensitive; if tissue becomes too acidic, the metabolic pathways can't function properly. In other words, the horses are running out of fuel and they have a harder time processing the fuel they still have. "They start shutting down," Thunes says.

After a race is over, a horse's body gets to work processing the lactic acid and, perhaps most importantly, restoring glycogen reserves. In humans, glycogen recoup takes about 24 hours. But horses take a lot longer—several days, in fact. Trainers make sure their charges drink plenty of water and sometimes even use intravenous fluids to aid that repair process.

One big complication: During a race, horses can bleed into their air passages. At the very least, this is uncomfortable, but it also causes inflammation and scarring. Worst case scenario they could drown in their own blood. So starting in the 1970s, many trainers started giving their horses a drug called Lasix, a diuretic that lowered overall fluid volume and reduced the risks of bleeds. An estimated 90 percent of racehorses now get it—the dropped water weight from its diuretic effect may also boost performance. (They are, literally, peeing like racehorses.) But horses on Lasix also lose 40 to 50 times more calcium, sodium, and other minerals than usual through that excess urine. Worse, horses on Lasix don't naturally become more thirsty to replace the vital fluids needed for recovery, so it takes a horse three days to return to its pre-race weight. By that point, horses still haven't re-balanced their electrolyte levels, which are essential for muscle conductivity and other bodily functions. Some experts say it's no coincidence that the Triple Crown drought started around the same time Lasix became a standard in the racing world.

The author of the Lasix study, Joe Pagan, president of Kentucky Equine Research and nutrition consultant to the United States Equestrian Federation, developed a two-step solution: First, horses get a concentrated electrolyte paste right after racing to boost their thirst. Then they get a daily electrolyte with added calcium to replace what was lost in their urine. With the supplements, horses rebound from their Lasix weight loss in 38 hours and come back from mineral losses within a few days.

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If a horse eats well and stays hydrated, their glycogen and electrolyte levels should return to normal between each leg of the Triple Crown, but they might be able to recover faster and be in better form for training between races with improved electrolyte supplements. Unfortunately for American Pharoah and the other contenders, Pagan's study just came out, so this development likely won't impact the horses competing in the Belmont this year.

Healthy Muscles

In addition to being the last race of the Triple Crown, the Belmont Stakes is also the longest. Some Derby contenders have never raced a mile and a quarter before, never mind the mile and a half they need to run for the Belmont Stakes. Most thoroughbreds also typically get three weeks to a month between tough races, while the Triple Crown allows for just a few weeks between each race.

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That's no easy feat, even for a racehorse. When a horse runs a tough race (or has a new workout at a longer distance), its muscles break down. Then, during rest, they reknit and adapt. Your muscles do the same thing. "It's a part of exercising at the top of their game," Thunes says. "You have to give them time before ramping them up again over a new distance." The trio of strenuous races combined with minimal downtime pushes horses to their limits. For many horses, the time between the Derby and Preakness might not be enough time to heal completely, leaving them with even more muscular damage to deal with before the Belmont.

But trainers who skip one or two of the earlier Triple Crown races can set their horses' rest and workout schedule so they peak at a muscular (and mental) level for the Belmont. American Pharoah, for example, had to take it easy the week after the Preakness. His Belmont prep was a slow build-up from there, concluding with a fast mile and a half gallop on May 30 and a final workout at an easier pace and shorter distance on June 1. A horse that has skipped the Preakness, however, has the luxury of time. Mubtaahij, for example, who finished eighth in the Derby, had plenty of rest so he could be pushed for hard workouts two weeks prior to the Belmont. Now, his trainer hopes to keep his colt fresh by taking the week leading up to the race easy. Pharoah's trainer is a pro, but having the time to relax and physically rebuild during this final week could make all the difference on race day.

Dem bones

At different points in its stride, a galloping horse puts all its weight on a single leg. That limb bears three times more weight than usual when galloping on a straightaway and, thanks to centrifugal force, a load five to 10 times greater on turns. This translates to skeletal microdamage.

That damage can manifest as anything from bone strain to microscopic cracks. "The skeleton is dynamic and the body is continually revitalizing the skeleton by removing damage and replacing it with healthy bone tissue," says Sue Stover, a professor at the UC Davis School of Veterinary Medicine.

Luckily, the 3-year-olds that run the Triple Crown are young, healthy athletes with bodies that adapt faster than those of older horses, and "remodeling" ultimately makes bones stronger. But another side effect of Lasix, it turns out, is slower healing—they lose bone-building calcium, remember, through all that diuretic-induced pee. Even mild microdamage can manifest as discomfort or soreness, taking the edge off during competition. Bones also become weaker between the time when the body removes the damaged material and when it finishes rebuilding that area. Race a horse during that critical period and you increase the risk of serious injuries mid-race. A fresh horse won't face any of those problems. Even a horse that ran in the Derby but skipped the Preakness will have five weeks to rest, and plenty of time for normal skeletal damage to repair, before the Belmont.

So, American Pharoah, it'd be awesome if you win the Triple Crown, but you probably won't. It's not your fault. It's science and those pesky fresh horses. Frosted, for example, who came in fourth in the Derby and sat out the Preakness (and who happens to be a half-brother to last year's Triple Crown buster, Tonalist, and is being ridden by the same jockey, too) is most likely to spoil the party. But that shouldn't stop someone, hypothetically, from placing a hopeful bet.