Do you lose your mtn-bike fitness after an injury?

Credit: Brian Bahr/Allsport
What happens to the highly conditioned off-road cyclist who has fine-tuned their performance skills to a peak level, only to have their competitive season and daily training come to an end due to a crash?

Most cyclists agree that it is bad enough to suffer the pain of an injury, but it is even worse when the condition forces them to stop training. Most athletes fear that all they have gained through hard training will be lost after a few days or weeks of inactivity.

Recent studies have made it clear that a few days of rest or reduction in training will not impair performance, and may even enhance it. It is logical, however, that at some point a reduction in training, or complete inactivity, will produce a deterioration in performance.

When a cyclist breaks a leg or severely injures a ligament or tendon and the limb is placed in a rigid cast to render it completely immobile, changes immediately start taking place in both the bone and surrounding muscles. Within a period of only a few days, the cast, which was applied very tightly around the injured segment, becomes quite loose. By the end of the several weeks, there is a large space between the cast and the limb. Is this the result of the cast expanding with use, or does the limb decrease in size with disuse? It is now clearly understood that skeletal muscle cells will undergo a substantial decrease in size with inactivity. Accompanying this decrease in size is a considerable loss in strength, power and endurance capacity.

Unfortunately, the muscle cells gain from miles and miles of cycling are quickly lost when you stop training. If for some reason you are unable to train for just one week, the muscle's aerobic energy declines to 50 percent of its trained level. Some physiologists have shown that the muscle's enzymes (biochemical catalysts that speed up energy production in the muscles) may begin to decline within just 48 hours if the muscles are not exercised. After an additional week of inactivity, the muscle's endurance capacity remains about the same, though it still seems more capable of energy production than an untrained muscle.

Another important change that takes place with the cessation of training, often referred to as "detraining," is a reduction in the number of small blood vessels (capillaries) that surround each muscle cell and deliver oxygen and blood-carried fuels such as glucose and fats. Studies have shown that the number of capillaries around each muscle cell decreases by 10 to 20 percent between five to 12 days after the last training session. As a result, the delivery of oxygen to these muscle cells and their ability to produce energy are dramatically impaired.

According to Edward Coyle, Ph.D., exercise physiologist from the University of Texas, who has studied detraining, VO2 max drops quickly in the first month of inactivity. The loss of oxygen capacity slows with time, but continues for many months.

Other changes are also taking place within the cardiovascular system. Specifically, the capacity of the heart to pump blood during maximal effort begins to diminish within the first five to 12 days of inactivity. In combination, the lowering of the heart's ability to pump blood and the decrease in blood flow to the muscle cells lessen the transport of oxygen to the cyclist's muscle cells and slows the removal of waste materials from the working muscles.

One of these waste products is lactic acid, the result of the muscle's efforts to produce energy without sufficient oxygen. A well-trained cyclist produces very little lactic acid during a long ride, since oxygen delivery to the muscles is good. With the cessation of training and the subsequent weakening of the oxygen transport system, lactic acid levels increase in the blood and muscles.

When you stop training, however, the physiological changes associated with the muscle's ability to produce energy do not all decline at the same rate. The big question here is, how quickly will performance be affected after you stop training?

In general, as we have discussed, there is no loss in performance for five to seven days. As a matter of fact, cycling performance may even improve after two to five days of inactivity. Such "rest" periods allow the muscles and nervous system to recover and rebuild from the stress of heavy training, thereby providing the cyclist with improved reserves and greater tolerance for endurance exercise.

In light of these physical transformations that accompany detraining, how much and how often do you need to train to maintain your conditioning after a minor injury or illness? Though no precise answer can be given, but some research shows that a trained cyclist can ride for 45 to 60 minutes every second or third day without showing any physiological losses. Of course, such a routine can only be used for a limited period of time before the body begins to adjust the systems downward.

After several weeks or months of layoff, you can't expect to gain back your conditioning with a few hard training rides. How quickly you regain your fitness depends on the duration of the lapse in training and what activities you have been doing during the detraining period. Although the picture is not absolutely clear, it appears that the rate of deconditioning is unrelated to how long you have previously been training.

Regardless of whether you have been training for six months or six years, an interruption of eight or 10 weeks will wipe out 80 to 100 percent of the conditioning gains.

The first step in self-treatment of most injuries is active recovery. Recovery shouldn't mean total inactivity, unless the injury is severe. Recovery means less activity, rather than no activity.

Online training diary: Use Training Bible to record your mileage and vital stats, and gear up for your next race.

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