This chapter serves as an introduction to the volume focused on the molecular and cellular regulation of adaptation to acute and chronic exercise exposure. It begins with a definition of the overall content of the “sedens–physical activity–exercise training–fitness” domain. One conclusion from this brief overview is that past and current studies have primarily dealt with very limited subsets of the traits and parameters of interest to exercise biologists. Molecular and cellular studies have focused more on adaptation to exercise and less on variable levels of cardiorespiratory fitness even though the latter is a powerful indicator of current and future health status and longevity. In this regard, molecular profiling of intrinsic versus acquired cardiorespiratory fitness would seem to be an area of research deserving more attention. Although molecular and cellular studies are clearly reductionist by nature, they constitute the primary material allowing systems biology to draw inferences about pathways, networks, and systems. Integrative physiology can be substantially enriched by taking advantage of the findings and lessons from molecular studies and systems biology approaches. DNA sequence variation within and between populations as well as recent advances in the definition of the functional elements in the human and other genomes offer unique opportunities to pursue new and more powerful molecular studies, and to reconcile reductionist and integrative approaches.
