The response to exercise training is often described in general terms, with the assumption that the group average represents a typical response for most individuals. However, in reality, it is more common for individuals to show a wide range of responses to identical exercise programs. In 1999, a large study published by Claude Bouchard and colleagues, reported that 20 % of us show little or no gain in maximal oxygen consumption (VO2max) with exercise training. This is a concern, since a high VO2max is associated with decreased rates of cardiovascular morbidity and mortality. Exploring the phenomenon of high responders and low responders following the same exercise program may provide helpful insights into mechanisms of training adaptation and methods of training prescription.