Obviously the purpose of any training session is to place a specific stress on a physiological system so that the resulting response will produce a positive adaptation in that system and a subsequent improvement in training capacity or performance. If follows, then, that a training session is beneficial only if it, forces the body to adapt to the stress of the physical workload. If that stress is inadequate to overload a physiological system, then no adaptation will occur. Conversely, if the workload is too great-that is, applied too quickly-or performed too often without without adequate rest, then fatigue follows, and the resultant performance will be impaired. The effectiveness of a stressor in creating an adaptive response is specific to each athlete and depends on a variety of factors, such as current state of fitness, the time elapsed since the last workout, environmental conditions and a multitude of other subtle influences. It is the role of the coach to ensure that training programs are structured such that the athlete attains the maximal possible physiological adaptations while reducing the risk of residual fatigue, which may result in illness or injury.