Personal Trainer
Paul O'Brien
Training for an endurance event such as a marathon or a triathlon entails improving your body’s ability to fight the onset of fatigue.
But what causes your body to tire? Generally, there are three major causes: a build up of waste products in the muscles, an inadequate supply of fuel to the muscles or muscles simply failing to contract or work properly. The reason you fatigue at any given time could be down to one of these factors, or a combination of all three.
Waste build-up
Lactic acid is a by-product of the breakdown of carbohydrates for fuel at the cellular level. The higher the intensity of your exercise, the more lactic acid accumulates in the muscles.
At low intensity, lactic acid does not build up to a level that causes fatigue, as the body can easily remove it. However, as intensity increases, the build up of lactic acid begins to outstrip the body’s ability to remove it. When this reaches a certain point, the muscle stops working.
For endurance events, lactic acid build up is not the major cause of muscle fatigue. You may be more likely to experience this during speed training, or climbing a long hill during an event or at a sprint finish in a distance cycle race.
Tip: Use short, high-intensity training sessions followed by long recoveries.
Low on fuel
By far the more common cause of muscular fatigue in endurance events is a lack of adequate fuel. If you are competing at a fairly low intensity, such as walking or jogging, you may not be too bothered by this. However, as intensity increases, the body burns more carbohydrates than fat as the major fuel source. If your body isn’t trained to conserve this fuel source, it will quickly burn out.
For example, during the Gaelforce West event last year, I experienced this fuel depletion fatigue on the Croagh Patrick ascent. My leg muscles simply gave up and I had to wait 15 minutes before the glucose drinks I slammed down provided enough energy to see me (slowly) through to the end. An event like Gaelforce could easily torch 1,000 calories per hour, so it’s easy to see how fuel reserves can become depleted.
Tip: The way to prevent this is twofold – ensure adequate reserves of complex and simple carbs in your diet, especially in the weeks before the event. Performing moderately hard workouts at close to your projected race pace will also teach your muscles to conserve carbs and use more fat as fuel.
Shut down
Sometimes muscles also just stop contracting. No one really knows why. It may be something to do with the nervous system, when the brain sends a message to a muscle to stop contracting in order to prevent possible injury.
Tip: The way to train this is, again, to train at higher intensity once every seven to ten days. Train at race pace or perform a speed session, followed by a couple of days of easier exercise or rest.
Knowledge is power. Use this information and the training tips included and you’ll be less likely to hit that most familiar of endurance obstacles next time around – the wall!
