Vöðvaþráða

Vöðvaþráða, the Icelandic term for muscle fiber, refers to the individual cells that make up skeletal muscle tissue. These are long, multinucleated cells, often referred to as muscle fibers, that are specialized for contraction. Each vöðvaþráða contains myofibrils, which are rod-like structures composed of repeating units called sarcomeres. Sarcomeres are the fundamental contractile units of muscle and are built from two main types of protein filaments: actin and myosin.

The contraction of a vöðvaþráða is a complex process initiated by a nerve impulse. This impulse triggers a cascade of events involving the release of calcium ions within the muscle fiber. These ions then bind to regulatory proteins, allowing the actin and myosin filaments to interact. The myosin heads bind to actin, pull the actin filaments towards the center of the sarcomere, and then detach, a cycle that repeats and shortens the sarcomere. This shortening of numerous sarcomeres throughout the muscle fiber results in muscle contraction.

Vöðvaþráða can be broadly categorized into different types based on their contractile properties and metabolic characteristics, primarily slow-twitch (Type I) and fast-twitch (Type II) fibers. Slow-twitch fibers are more resistant to fatigue and are involved in sustained, lower-intensity activities like endurance exercise. Fast-twitch fibers, on the other hand, contract more forcefully and rapidly but fatigue more quickly, playing a role in explosive movements and high-intensity activities. The proportion of these fiber types can vary between individuals and can be influenced by training.