Final answer:
The gross energy expenditure during activities such as treadmill running is determined by the basal metabolic rate, frictional forces, and the work required to counteract gravity, particularly during uphill activities where increased energy is utilized.
Step-by-step explanation:
The total rate of energy expenditure (gross) during steady-state treadmill walking or running is a function of three main components: the basal metabolic rate (BMR), the energy used to overcome frictional forces, and the energy required to work against gravity. In activities like jogging on a slope, gravity plays a larger role as additional energy is needed to elevate the body against the pull of gravity. This is apart from the energy required to overcome friction and maintain the body's BMR, which includes sustaining organ function and other essential physiological processes.
The energy used in activities is significantly related to power output and the efficiency of the human body as a 'machine'. During vigorous activities, such as running uphill, the power requirements increase due to the added effort needed to work against the incline. Additionally, the body's efficiency affects how much of the food energy consumed is converted into useful work.