During physical activity, your muscles are constantly working. The longer and the harder you work, your breathing rate will increase as well (you will breathe harder). What two
body systems are working together here?

The answers are the Respiratory system and the Muscular system.

Explanation:

Respiratory system:Your respiratory system is the network of organs and tissues that help you breathe. This system helps your body absorb oxygen from the air so your organs can work. It also cleans waste gases, such as carbon dioxide, from your blood.

Muscular system:The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction.

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