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Fitness Decline From an Injury

Dear Speed Lab,
I am presently recovering from injury and I was wondering how long it takes to lose the gains in fitness achieved prior to an injury. If there are major losses, what are they?

Greenville, North Carolina

Injured athletes commonly fear that the fitness they have gained through hard training will be lost after a few days or weeks without training. It is true that at some point a reduction in training or outright inactivity will result in a deterioration of performance.

Unfortunately, fitness is quickly lost when the athlete stops all training. With the cessation of training, improvements in VO2 max, maximal cardiac output, skeletal muscle capillarization and the aerobic capacity of the arm/leg muscles vanish at varied rates.

If, for some reason, the endurance athlete is unable to train for just one week, the muscles' aerobic capacity may decline by 10 to 15 percent. This finding is supported by observations that the activities of the mitochondrial enzymes are dramatically reduced with the cessation of exercise. The concentration of these enzymes may start to decline as early as 48 hours after stopping exercise.

Another important change that takes place as a consequence of detraining is a reduction in the number of capillaries, which deliver oxygen and nutrients and surround each muscle fiber. This decrease can be as much as 10 to 20 percent within five to 12 days after the cessation of exercise. This results in the impairment of oxygen delivery and the ability of the cells to produce energy.

During the same period of inactivity, the capacity of the heart to pump blood during a maximal effort starts to decrease. The combination of a lower maximal cardiac output and reduced blood flow around the muscle fibers lessens the transport of oxygen to the athlete's muscle fibers and slows the removal of waste products (e.g., lactic acid) from the working muscles.

The burning question: how quickly will exercise performance be affected after an athlete stops all training? In most cases a measurable loss of performance will be observed after five to seven days and will steadily increase as the duration of the layoff increases.

1. Costill, D.L., Fink, W.J., Hargreaves, M., King, D.S, Thomas, R. and Fielding, R. (1985). Metabolic characteristics of skeletal muscle during detraining from competitive swimming, Medicine & Science in Sports & Exercise, 17: 339-343.

2. Houston, M.E., Bentzen, H. and Larsen, H (1979). Interrelationships between skeletal muscle adaptations and performance as studied by detraining and retraining. Acta Physiol Scand, 105: 163-170.

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