Step-by-step explanation:
When a person is doing an exercise, the movement of his body parts represents mechanical energy. When a person performs an exercise for some time, the temperature of the person's body starts rising. Thus, it can be said that by doing exercise which is mechanical energy, the temperature of the person's body rises which is a form of thermal energy.
Thus, when a person performs an exercise, mechanical energy is transformed into thermal energy.
Final answer:
Mechanical energy transforms into thermal energy.