Skeletal Muscle: The Key to Exercise and Sports

Welcome back! In this blog, I am going to discuss the basics of skeletal muscle anatomy and muscle contraction, which are important to understand because we use skeletal muscle during all kinds of movements in sports and exercise as well as in our daily activities.

Skeletal muscle is one of three types of muscle tissues (the other two are cardiac and smooth), and it is the only one that operates under voluntary control. In other words, we are able to consciously determine the activity of our skeletal muscle. The primary function of skeletal muscle is to contract, and to do so, it requires an impulse from a nerve cell. I won't go much more in depth regarding this process, but the main idea is that the nervous system plays a critical role in muscle contraction.

There are numerous skeletal muscles throughout the human body that vary in size and function. What are some of the most notable muscles for athletics? Let me introduce you to some of our largest muscles, with which you may be familiar if you are an athlete, particularly a weightlifter. In the upper body, the large muscles include the deltoid (shoulder), latissimus dorsi (back), and biceps brachii. In the lower body, the large muscles include the quadriceps (front of the upper leg) and gluteus maximus (buttocks).

Let's dive deeper and explore the elements of a single skeletal muscle from the outermost piece to the innermost piece. Each skeletal muscle is wrapped in epimysium (a connective tissue sheath) and inside, there are several bundles called fascicles. Each fascicle is surrounded by connective tissue called the perimysium and contains many long muscle fibers that are packed together and surrounded by connective tissue called the endomysium. Each muscle fiber contains numerous myofibrils, which consist of sarcomeres, the basic contractile unit. I know this is an enormous lump of information, so feel free to review it along with the diagram below.

Each sarcomere has alternating thick and thin protein filaments. The thick filaments are called myosin and are anchored at the M line at the middle of the sarcomere. The thin filaments are called actin and are anchored to the Z lines at the edges of the sarcomere. The presence of calcium ions and ATP causes actin filaments to slide along myosin filaments toward the M line. (The actin filaments don't slide by themselves; the myosin filaments form cross bridges that attach to the actin filaments, allowing myosin to pull the actin filaments across.) As a result, the sarcomere (as well as the entire muscle fiber) shortens. The final outcome of this process is a muscle contraction!

Before, you knew that skeletal muscle and muscle contraction are such integral components of our exercise, sports, and daily movement. Now, you understand the unique characteristics and components of skeletal muscle, examples of skeletal muscle, and the fundamental process of muscle contraction!