While a single workout alone, especially if it is new to an athlete, introduces a specific signal and activation of transcription factors, repeated workouts lead to a concerted accumulation of messenger RNAs that are translated into a host of structural and functional proteins. With endurance training, for example, the accumulation of proteins is manifested as an increase in the number of mitochondria, the microscopic aerobic factories in muscles responsible for aerobic metabolism. With strength training, the accumulation of proteins is manifested as an increase in the number of contractile proteins in muscles (actin and myosin).
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The greater the training stimulus, the longer the time needed for recovery and adaptation to the stimulus. If the training stress is too great and/or athletes don't recover before their next workout or race, their performance and ability to adapt to subsequent training sessions declines. The most effective adaptations occur when athletes are recovered from previous training and are best prepared to tolerate a subsequent overload. Therefore, what athletes do the rest of the day when they're not training is just as important as what they do when they are training.
While much of training is a science, with specific biochemical and physiological changes occurring through the use of specific workouts, it's an art to manipulate stress and recovery in an organized training program to achieve the greatest adaptation possible. As such, it needs to be practiced and fine-tuned like other forms of art.
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Factors That Affect Recovery
A number of factors affect how quickly and completely athletes recover from workouts, including age, training intensity, nutrition, environment, stress and level of fitness. The most significant of these factors is age. Younger runners recover faster between workouts, enabling them to perform hard workouts more often. Workout intensity is the next biggest factor, with higher-intensity workouts requiring longer recovery time. The athlete's environment also plays a role in recovery, with altitude and cold weather slowing recovery.
Since recovery is an aerobic process, a high level of cardiovascular fitness speeds recovery due to the quicker delivery of nutrients and removal of metabolic waste by the circulatory system. Nutrition and hydration are also big factors that influence recovery, with carbohydrates and protein being the most important nutrients.