What is a Muscle Strain?

A strain is an injury caused by excessive stretching to a muscle or musculotendinous unit, through either an unusual muscle contraction or over-stretching. The common signs and symptoms associated with strains include pain, swelling, muscle spasms, and a limited ability to move the affected muscle. The severity of the strains differs from injury to injury, and hence they are broadly classified into three categories; grade I, grade II, and grade II.

Three Grades of Strains;

Grade I strain

Some muscle and tendon fibres are torn, but the function and strength of the musculotendinous unit isn’t greatly affected. Moderate pain and swelling would be expected.

Grade 2 strain

A larger number of muscle and tendon fibres are torn, resulting in a greater loss of function and strength of the affected muscle. A greater degree of pain and more swelling would be expected.

Grade 3 strain

The muscle of the tendon is completely severed, resulting in complete loss of function and strength. Grade 3 strains are often so severe that they require surgical intervention to repair.


Muscle Strain Grades

How do strains heal?

There are three different phases associated with the healing of musculotendinous strains. These three phases include:

  • Inflammatory stage
  • Repair (proliferative) stage
  • Remodelling stage


Stages of Muscle Healing;

Inflammatory stage: 1-7 days

The inflammatory stage occurs immediately after the injury occurs. Capillaries surrounding the injury vasodilate (increase in diameter), increasing the amount of blood reaching the damaged site.  A mass of cells, called platelets, migrate to the injured site and create blood clots in the damaged circulatory vessels. Additionally, macrophages (white blood cells which function as part of the immune system) travel through your bloodstream and accumulate at the site of the injury, engulfing any pathogens or debris (such as dead tissue and dry blood) resulting from the trauma. It is expected for pain, swelling, warmth, redness, and reduced range of motion to be present at this stage.



Repair (Proliferative) Stage: 6 days to 2-3 weeks


Once the inflammatory stage is over, there is a rapid increase in cells at the site of the trauma, as well as the penetration of nerves and blood vessels into the wound area. These nerves and blood vessels are essential in the healing process as they supply the cells with the materials needed to commence the formation of new tissue. In skeletal muscle, satellite cells (cells which promote the growth, repair and regeneration of skeletal muscle fibres) develop into myoblasts, which are the precursors to muscle cells. These myoblasts aid musculotendinous healing by fusing to each other, as well as existing muscle fibres, resulting in new skeletal muscle formation. Additionally, in tendon tissue, cells called fibroblasts start to produce collagen fibres (the principle components of tendons) and hence commence repairing damage to the tendon caused by the strain. In addition to this, new blood vessels and nerves are formed to supply and innervate the repaired site.



Remodelling: 2 weeks up to 12months


Remodelling is the final stage of musculotendinous tissue healing and can last up to 12 months before completed. It involves a reduction in scar tissue at the site of the injury, as well as the maturation and alignment of the newly regenerated muscle fibres and connective tissue. This is achieved through appropriate stretching and strengthening exercises.

Stages of Muscle Healing