Although intensive exercise protocols are commonly used in practical training and scientific studies, there is recently a great scientific discussion about "high intensity (interval) training" (HIT). New are the large amounts of studies and the more detailed knowledge about the physiological responses and adaptations to HIT in comparison to the classic high volume, low intensity endurance training. The present article summarizes the current knowledge about HIT in endurance exercise for clinical applications. In the first part, molecular and cellular adaptations to HIT are discussed in comparison to low intensity high volume training. Furthermore, studies are summarized which compare HIT vs. HVT in the field of prevention and rehabilitation. Terminally the differences in physiological stimuli of both training interventions are considered.