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When muscles rebel


FLOORED BY FATIGUE Athletes are stopped in their tracks when muscles cramp or refuse to work.

Pro tips on overcoming fatigue in training and endurance events

Paul O'Brien

Fitness, at least in terms of what’s required for endurance events, boils down to improving your body’s ability to limit the onset of fatigue. In ’80s marathon-speak, reaching this point of fatigue during training or events was called ‘hitting the wall’. It’s since been extended to include any endurance event – distance cycling, triathlons, ultra-endurance events and longer-distance adventure races. Thankfully, sports science has advanced our knowledge considerably since the 1980s. We now know that fatigue is caused by inadequate fuel supply to working muscles (cellular depletion), a build-up of waste products in the muscles or the simple cessation of a muscle’s mechanical function.
A muscle could be forced to stop for any one or a combination of all of these factors. Trying to push a muscle further once these kick in usually leads to the brain taking charge and forcing a muscle to stop working either through extreme cramp or, less subtly, injury.

The Fuel
The major cause of muscle fatigue and failure in distance endurance events is either a lack of adequate fuel to the muscle cells or an inhibition in the muscles’ ability to assimilate fuel and use it for energy. These too are closely related. At higher intensity, the body begins to deplete its major source of fuel, which comes from dietary carbohydrates stored in the body as glycogen in the liver and muscles mainly. The body can store up to about 3,000 calories worth of glycogen, most of which is held in skeletal muscle.

Quick burn
During endurance events, your body can burn up approximately 1,000 calories per hour. So, if your event exceeds two hours, you begin to run low on stored fuel. After three hours, you will be most likely depleted of your original fuel and will experience depletion and fatigue, unless you have employed one or both of the following strategies.

Fighting fatigue
Firstly, take on extra fuel during your event or training. After the first hour, consuming 300-500 calories per hour for every subsequent hour can help to offset the onset of fatigue.
A second and less-understood strategy is to use high-intensity training in your weekly schedule. Sessions like hill runs and tempo sessions at close to or on projected race pace can teach your muscles to more effectively conserve glycogen by using stored fat as an added fuel source. These sessions should be well structured and preferably under the instruction of a professional.

Feeling the burn
Lactic acid, a by-product of muscular contraction, increases in your muscle cells as the workload upon your muscles increases. At lower intensity, your body flushes this out before it becomes a problem. At higher intensity, which could be longer distance and not just faster-paced training, lactic acid build-up begins to outstrip the body’s ability to remove it. This also causes muscular fatigue and is the most common cause of cramping.
Sprint training is a very effective way of improving your muscles’ tolerance to lactic acid and should be considered in your training regime, again as part of a structured programme.
At times muscles may just stop contracting. The cause for this is uncertain. 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.  Training at higher intensity once every seven to ten days can also help to prevent this occurring.
Ultimately, beating fatigue means fueling your body with an optimal diet and mixing up your training using high-intensity workouts can help prime your body and overcome some of the obstacles that hinder your training.

Paul O’Brien is a certified personal trainer with the American Council on Exercise since 2007 and a qualified Life, Health & Nutrition Coach. He is co-owner of Republic of Fitness in Westport. He can be contacted on 086 1674515 or