Throughout most of the 20th century, the prevailing theory of exercise fatigue was the so-called "catastrophe" model. According to this theory, fatigue is an involuntary drop in performance caused by the loss of homeostasis (balance) somewhere in the body. For example, owing to lactic acid build-up, the pH balance in the muscles is upset and becomes too acidic for them to function properly, causing you to slow down. Or the muscles become depleted of glycogen (their primary fuel source) so there’s no longer sufficient energy available to sustain performance. However, in the 1980s a new generation of exercise scientists, led by Professor Tim Noakes of the University of Cape Town, South Africa, began to poke holes in the catastrophe model. First, they found that the common functional breakdowns – things like lactic acid build-up and glycogen depletion – don’t always occur as we tire. In fact, studies showed that fatigue often develops before the muscles reach a level of acidity that would cause direct muscle dysfunction, and that you can feel tired even when there is still muscle glycogen available in the working muscles. What’s more, these researchers also argued that the old catastrophe model couldn’t account for the peculiar phenomenon known as the "end spurt" – the ability to pull a sprint finish out of the bag at the end of a marathon. If fatigue was always caused by direct physiological events within the muscles, runners who began to slow down during the latter stages of a race couldn’t possibly sprint the last 100 yards or so. "Athletes can often surge during the latter stages of a race, knowing that they won’t have to continue once they cross the finish line," says Chris Abbiss, a biomedical and health science researcher at Edith Cowan University in Western Australia. In one 2001 experiment on end spurts, Australian researchers put a group of subjects through a 60-minute simulated time trial on stationary bikes. They interspersed six all-out sprints throughout the hour-long effort. The results showed that maximum power output began to decline in the second sprint, indicating a very early onset of fatigue. Maximum power continued to decrease through the fifth sprint, but then suddenly shot up in the sixth and final sprint. If the fatigue that began to set in as early as the second sprint had been caused by a catastrophic loss of homeostasis in the muscles, where did the cyclists find the energy for the final surge? | |
Are We Finished Yet?As more research challenged the catastrophe theory of fatigue, an alternative emerged, suggesting that fatigue is a protective mechanism that the brain uses to prevent a catastrophic breakdown. Feedback signals from the body to the brain indicate the imminent likelihood of a physical crisis if exercise continues at the current intensity level. In response to these signals, the brain decreases muscle activation and produces feelings of discomfort and loss of motivation, resulting in reduced exercise performance. That is, your brain tells your body to stop working so hard.The new, brain-centred model of exercise fatigue – called the central governor theory – also explains the end spurt. Proponents of this model believe that, throughout exercise, the brain continually reads feedback signals from the muscles, blood and elsewhere in order to answer the question "How much longer can my body go at the present work level before something terrible happens?" When the answer received is "not much longer", the brain reduces motor output to the muscles and generates those familiar feelings of suffering to reinforce the need to slow down. But when the finish line is within sight, your brain allows you to pick up the pace, knowing it will all be over soon. "The brain diminishes muscle activation in the middle of the race in anticipation of calling in a reserve towards the end," says Frank Marino, head of the School of Movement Studies at Charles Sturt University in Australia. |
The Power of Thought
If fatigue really does start in your head, how do you train to delay its onset? By doing sessions that will convince your "central governor" that you’re capable of achieving your goal times without suffering bodily harm. Such sessions should be highly race specific – simulating both the pace and the distance of your goal event – so that your brain will be less likely to feel endangered during the race and won’t put the brakes on motor output to your muscles, causing you to hit the wall.The perfect example of a highly race-specific session for a 5K runner is an interval session of 5 x 1,000m at 5K race pace, with three-minute jog recoveries between the efforts. Because the session entails running 5K at 5K goal pace, it serves as proof to the brain that your body can handle the workload. If you’re training for a longer race, such as a half-marathon or a marathon, you need to alter this approach by running only about half the race distance at goal pace, since not even the toughest elite runner could recover quickly enough from a session totalling 26 miles of race-pace intervals.
Most runners can’t jump right into demanding race-specific sessions without first developing the speed and distance components of race fitness individually. So start by doing one challenging speed session and one challenging distance session each week, along with however many easy runs you want.
Early on, most of your speed training should be much faster and your distance training much slower than goal race pace. As your body adapts, your speed efforts should become longer and slower, your distance efforts longer then faster, until your sessions closely simulate the upcoming race experience. Once you have proven to your brain that you can complete these race-specific sessions, come the big day it should respond to your efforts with a "been there, done that, no problem."
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BUILD 2 3 TO 4 WEEKS Sessions to get your mind and body in shape and in sync | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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