Final answer:
When a person is engaging in physical activity, the nervous system and muscular system work together to contract muscles. Different activities target different muscle groups.
Step-by-step explanation:
When a person is engaging in physical activity, the nervous system and muscular system work together to contract muscles. This is because the nervous system controls muscle contractions by sending electrical signals through motor neurons to stimulate muscle fibers. The muscular system consists of different types of muscle tissue, including skeletal muscles that move the skeleton, cardiac muscle in the heart, and smooth muscle in organs like the digestive tract.
The statement that all muscle groups are stressed to the same extent during physical activity is not true. Different activities target different muscle groups. For example, running primarily engages leg muscles, while swimming engages muscles in the arms, back, and legs.