03/03/2022
The racehorse’s mortal enemy…
The very conformation adaptations that make a horse so fast are the ones that make it imperative that he is fully prepared to face any athletic demands placed on him. You see, horses do not have any muscles below their knee and hock joints in their legs…that’s right, it’s nothing but a complex combination of bones, tendons, and ligaments supporting the entire weight of a racehorse in full stride. While muscles are stretchy, especially once warmed up, tendons and ligaments are not. This is part of the genius evolutionary design of a horse that allows the massive muscles up high to leverage the kinetic tensile strength of sinew down low and convert it into raw speed with minimal effort, relatively speaking.
But what happens when the muscles reach a point in their exercise where they can no longer produce the level of effort required to continue to propel a horse who’s still trying his heart out?
The F word… FATIGUE
With fatigue, the horse’s forearm muscles, the flexor muscles that are holding up the fetlock, relax their tension, causing the tendons and ligaments to absorb more of the mechanical stresses of running. The fetlock droops towards the ground, delaying the breakover of the foot (even worse if the foot has a long toe and low heel like so many racehorses do) and puts unnatural strain on the tendons as the hoof tries to roll over the toe at the end of the stance phase of the stride. At the very least this is a recipe for tendon strain, at the worst the consequences can be catastrophic.
Fatigue comes in four varieties: (1) lactic acid buildup; (2) fuel depletion; (3) structural fatigue; and, (4) metabolic fatigue. Any of these can begin a cascade of failure that can see a horse receive a career ending injury, or worse. If you can delay fatigue so that it doesn’t show up during the time that a horse is training or competing, you’ve defeated it, and made your horses exponentially safer in the process.
Each form of fatigue has its own set of causes and remedies…
Lactic Acid Fatigue: Lactic acid appears when fast twitch muscle cells are firing rapidly burning glycogen as fuel anaerobically, without oxygen. This type of muscle action is powerful, but inefficient and produces waste products in the cells including lactic acid. Lactic acid fatigue is essentially muscle cell paralysis due to the accumulation of lactic acid in and around fast twitch muscle cells.
The best way to combat lactic acid is through thorough training. A horse’s body will adapt remarkably to withstand the stresses it faces if they are brought on gradually enough that no bodily systems fail before the training effects take place. In the case of lactic acid, it is through sustained workloads producing medium to high lactic acid levels that produce changes within the muscle cells which allow the horse to delay the buildup of lactic acid to fatiguing levels.
Fuel Depletion Fatigue: In a fast moving horse, the fast twitch muscle cells are doing much of the work. The fuel source for these types of muscle cells is called glycogen, and it's stored in the bloodstream and within the muscle cells themselves. Not only do these fast twitch muscle cells rely on glycogen for fuel, but another, more important organ does as well…the brain. When glycogen stores start to dwindle as is the case when a horse has exerted himself in a race or strenuous workout, the horse’s body has a mechanism to prevent the stores from being completely depleted, which would have disastrous results for the brain, and it works by shutting off the muscle cells’ ability to burn glycogen. Without access to fuel, the muscle cells can’t fire and the horse slows down.
Preventing this kind of fatigue is pretty easy…make sure the muscle cells are filled to the brim with fuel. If a horse is trained properly, and fed appropriately for the work he is doing, he will gain weight, not in the form of stored fat, but in the form of muscle mass, aka fuel storage.
The next two types of fatigue have the same remedy, and therefore are closely related…structural fatigue can best be illustrated by thinking of a paperclip being bent back and forth until it breaks. Any repetitive motion performed in excess of the body’s rebuilding capabilities will cause breakdown of the structures bearing the burden of the exercise. Likewise, metabolic fatigue is a breakdown in the body’s fueling systems caused by overtaxing races or workouts followed by insufficient rest and recovery time.
The cure for both of these systemic overloads is patience and rest. Taking care not to progress too quickly on to heavier workloads while allowing plenty of time between taxing efforts will allow the horse’s body to respond favorably to increasing demands, becoming stronger with each stage of training.