Table of Contents Track and Field Events Warming up Training Training Tips Cells and Bones Joints and Muscles Movement and Muscle Fibers Energy Production in the Body The Cardio-respiratory System Nutrition and Calories Nutrients, Proteins and Carbohydrates Fats, Vitamins, Minerals, Water and Fiber Record Breakers Did you know? (Cool Track Facts) Track and Field Links Bibliography Chimacum Middle School ThinkQuest Jr. Please give us Feedback about our site. Contact us! Meet the Team Featured site: The International Amateur Athletics Federation

Around the Track and Back Anatomy and Phisiology Basics, cont'd: Joints Bones are moved at joints by the contraction and relaxation of muscles. We have over 600 muscles in our body and they make up 40% (that's almost half) of our weight! Muscles are bundles of long, thin cells called muscle fibers. Each bundle of fibers is held together by a tough sheath. Groups of bundles of fibers are also held together by a tough sheath. At the end of a muscle sheaths join together to form tendons which connect the muscle to bone. Muscles and Movement There are always two sets of muscles attached by tendons to bones. Movement will happen when a muscle pulls on a bone, muscles can only pull they can never push. So in order to move your arm there are muscles going up and down both sides of the bone in the upper arm, the humerus, which connects to the bones in the lower arm, the radius and ulna. On the back of the upper arm, the muscles are called triceps and on the front of the upper arm, the muscles are called biceps. When the biceps pull on the bone, or contracts, the arm bends at the elbow so that you can bring your hand up to your face for example. When the biceps contract, the triceps are relaxed. In order to straighten the arm again, the triceps need to pull on the bone, contract. At this point, the biceps are relaxed. The biceps can only bend the arm and the triceps can only straighten the arm. That's how muscles and bones work together!