Muscles contract and relax simultaneously to enable use to move. For example, our biceps and triceps work together, each contracting or relaxing to enable our arm to move. Muscles also assist in the transportation of blood around the body. For example in veins which carry deoxygenated blood back to the heart, muscles around the veins Contract and relax to facilitate this process. The heart and arteries are also have numerous muscles working together to pump blood thrroughout the body
