1. Running By: Ryan Teahan

2. Cardiovascular System and Lungs When your muscles need more oxygen to maintain their rate of contraction, your body will signal your heart to beat faster so that the blood will move faster through your circulatory system to meet the increased need. Simultaneously, your rate of breathing will increase as your lungs attempt to take in more air so they can obtain more oxygen to transfer to the blood.

3. Musculoskeletal System Although your upper-body muscles might contribute to maintaining a steady momentum and helping you balance, running primarily relies on muscles in your lower body, including the hamstrings and quadriceps. The contractions of the muscles of your lower body propel you forward because they are attached by tendons to your bones. Different bones are connected at the joints by ligaments, which allows them to bend as you run.

4. The Effect of Running People in excellent physical shape have strong muscles and cardiovascular systems, so they can run for long periods and at high speeds. For example, their powerful hearts pump blood more efficiently, which increases their endurance because the various body systems receive the oxygen they need to perform at a high rate. But people who are not physically fit won't be able to run as long because their relatively weaker cardiovascular systems can't keep up with the physical activity, so they must stop to catch their breath.

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