Why do humans vary in their responses to exercise training?

The concept of human variation in response to exercise training has been introduced about 30 years ago. Since the early 1980s a number of studies have supported this concept. In addition, several studies have shown that there is a genetic component that may explain the interindividual variation to training adaptations.

Professor Claude Bouchard, a pioneer on genetics of human adaptability to training, has summarized the available evidence in a review article last year.

You can download the paper from the Experimental Physiology at  http://ep.physoc.org/content/97/3/347.full.pdf+html