A muscle is surrounded by an outer sheath that allows it to move smoothly over the surrounding tissues as it contracts. Inside the outer sheath are bundles of muscle fibers known as fascicles, which are further made up of myofibrils. These myofibrils are composed of millions of microscopic units called sarcomeres that are responsible for muscle contraction. In the sarcomere, muscle proteins called myosins pull against thin ropes of protein called actin when they are stimulated by nerves. When this occurs, the sarcomeres shorten, resulting in a contraction. When the myosin proteins relax, the sarcomeres lengthen back to their original position and so does the muscle.

Muscle injuries is a broad term encompassing many pathologies and these are common injuries in both elite and amateur athletes as well as in the general population.

Skeletal muscles injuries represent a great part of all traumas in sports medicine, with an incidence from 10% to 55% of all sustained injuries.

A muscle strain is an injury to a muscle or a tendon — the fibrous tissue that connects muscles to bones. Minor injuries may only overstretch a muscle or tendon, while more severe injuries may involve partial or complete tears in these tissues.

A muscle strain, or pulled muscle, occurs when your muscle is overstretched or torn. This usually occurs as a result of fatigue, overuse, or improper use of a muscle. Strains can happen in any muscle, but they’re most common in your lower back, neck, shoulder, and hamstring, which is the muscle behind your thigh.