This chapter focuses on the application of the first and second laws of thermodynamics in the context of physical activities such as running, cycling, and weightlifting. Initially, the analysis was conducted with runners. Nevertheless, there were challenges in accurately measuring the work performed by the body due to the level of physical activities, as shown in the group studies. Later, a higher focus on cyclists demonstrated the feasibility of evaluating the internal body temperature and the distribution of temperature throughout the body. Such findings paved the way for a comprehensive phenomenological evaluation of the behavior of the human body over time. In the following sections, a logical analysis was conducted to demonstrate the research field formation and consolidation effectively. In the biomedical literature, there is a discrepancy regarding the calculation of the first law efficiency of the human body and its trend. The weightlifting must have some sensors to evaluate the power output better. The conclusions show that cycling is a valid tool to assess the human body efficiency since the performed power is measured. Results show that around 30% of the exergy of nutrients can be transformed into work. This type of exercise was the focus of the group after these conclusions to assess performance indicators and compare them with usual sports ones (maximum oxygen consumption, lactate threshold). The internal temperature, skin temperature, and skin wetness must be the focus of future analysis to guarantee the evaluation of a running may have a better instrumentation apparatus to guarantee a phenomenological precision in heat and mass transfer to the environment, and the only unknown variable be the power or focus on equations.