The goal of the Molecular Transducers of Physical Activity Consortium (MoTrPAC) is to assess molecular changes that occur in response to physical activity (PA). To achieve this aim, a mechanistic randomized controlled trial (RCT) is conducted, in which 1,980 adult study participants are randomized to endurance exercise (EE), training resistance exercise (RE) training, or no exercise Control for a period of approximately 12 weeks. The overarching hypothesis is that there are discoverable molecular transducers that communicate and coordinate the effects of exercise on cells, tissues, and organs, which may initiate processes ultimately leading to the health benefits of exercise. Because this is a mechanistic trial, the main goal is not a health-related outcome. Rather, the goal is to generate a map of the molecular responses to exercise that will be used by the Consortium and by the scientific community at large to generate hypotheses for future investigations of the health benefits of PA.