1. List the 3 main pairs of muscles. What are muscle pairs? Muscles commonly occur in groups of two, called muscle pairs. When one muscle in the pair contracts, the other relaxes, creating movement. The human body is made up of many different muscle pairs, although some are more important than others. Examples of three major muscle pairs are the biceps and triceps for bending and straightening the elbow, the quadriceps and hamstrings for bending and straightening the knee, and the deltoids and lattisimus dorsi for raising and lowering the arm.2. Describe the structure of skeletal muscles. What are muscle fibers made up of? A skeletal muscle is a type of striated muscle attached to the skeleton. The aim is to create movement by applying force to bones and joints. Skeletal muscles are made up of many smaller units called muscle bundles, and these are made up of even smaller units called muscle fibers. A muscle fiber is a single cell that contracts when stimulated. It consists of bundles of myofibrils, thick and thin filaments arranged in sacromeres. Skeletal muscles vary greatly in size, shape, and arrangement of these muscle fibers.3. Describe the sliding filament theory of muscle contraction. How is movement created? The sliding filament theory of muscle contraction is a theory that describes how muscles contract to produce force. In muscles there are both thick and thin muscle filaments within the sacromere. The thin filament slides over the thick filament to create tension in the muscle, shortening the length of the sacromere.4. Define the types (fast twitch/slow twitch) of muscle fibers and list their characteristics. Which type of muscle fiber has a better ability to use oxygen? Muscle fibers can be classified into two different types, fast-twitch and slow-twitch. On average we have about 50% slow-twitch fibers and 50% fast-twitch fibers in most muscles used for movement, although the percentage of each type of muscle fiber depends on a variety of factors such as muscle function , training and genetics. Slow-twitch fibers are more efficient at using oxygen to generate fuel for continuous, extended muscle contractions over a long period. As a result, this type of fiber is best suited for endurance activities such as marathons or long-distance cycling. In contrast, fast-twitch fibers are better suited to generating short bursts of strength or speed, but they fatigue more quickly.