The resistance of an exercise bike is often provided by a generator; that is, the energy that you expend is used to generate electric energy, which is then dissipated. Rather than dissipate the energy, it could be used for practical purposes. 

a. A typical person can maintain a steady energy expenditure of 400 W on a bicycle. Assuming a typical efficiency for the body and a generator that is 80% efficient, what useful electric power could you produce with a bicycle-powered generator? 

b. How many people would need to ride bicycle generators simultaneously to power a 400 W TV in the gym?