The energy requirements in response to physical activity differ between men and women. The differences are attributable to genetic and hormonal factors. Skeletal muscle metabolism is sexually dimorphic and is the composition of muscle fibers. The response of the cardiovascular system to exercise differs between the sexes, as does the composition of sex-specific substrate metabolism and ATP resynthesis. In spite of these markedly different features of the response to a demand for increased physical activity, women are still underrepresented in sport and exercise research.