How muscles, tendons and ligaments recover after an injury

After a sprain, a strain or a bruise, the body starts repairing the damage almost straight away. The process is gradual and it varies a great deal from person to person and injury to injury, but its broad outline is well understood. This page describes that outline in plain words, as a general picture rather than a prediction of what will happen with any particular injury.

What "soft tissue" means

The American Academy of Orthopaedic Surgeons explains in its OrthoInfo page on sprains, strains and other soft-tissue injuries that soft-tissue injuries typically affect muscles, tendons and ligaments, and most often occur during sport and exercise. Muscles are the tissues that contract to produce movement. Tendons are the cords that attach muscles to bones. Ligaments are the tough bands that join bones to one another and steady the joints. MedlinePlus, in its overview of sprains and strains, uses the same distinction: a sprain is a stretched or torn ligament, and a strain is a stretched or torn muscle or tendon.

These tissues are all built largely from long fibres of a protein called collagen, arranged in parallel bundles that let them take a pull along their length. Muscle has a rich blood supply; tendons and ligaments have a much thinner one. That difference is part of why injuries to different tissues tend to follow different courses.

Two ways tissue gets injured

OrthoInfo divides soft-tissue injuries into acute injuries, caused by a sudden trauma such as a fall, a twist or a blow, and overuse injuries, which develop when an activity is repeated so often that the tissues do not have enough time to recover before they are stressed again. The National Institute of Arthritis and Musculoskeletal and Skin Diseases draws the same line in its overview of sports injuries, noting that overuse, or chronic, injuries come from repetitive loading and develop gradually over time.

In an acute injury, fibres are stretched or torn at a single moment. In an overuse injury, small amounts of damage build up faster than the tissue can keep pace with, until the tissue becomes irritated and painful. The repair process described below applies to both, although overuse injuries tend to be slower to announce themselves and slower to settle.

The general stages of repair

Textbooks usually describe soft-tissue repair as a sequence of overlapping stages. The boundaries between them are blurred, and the pace of each varies with the tissue, the size of the injury, the person's age and health, and what they do in the meantime.

An early, inflamed stage

Straight after an injury, damaged blood vessels leak, and the area becomes swollen, warm, red and tender. This is inflammation, and although it is uncomfortable, it is also the first part of repair: the body sends cells to the area that clear away damaged tissue and release signals that set the next stages in motion. Pain in this stage acts as a warning to protect the area. The National Institute of Neurological Disorders and Stroke, in its page on pain, describes acute pain in exactly these terms, as a warning signal about a threat to the body from an injury or other cause.

A stage of laying down new tissue

As the inflammation begins to settle, specialised cells start laying down new collagen fibres to bridge the damaged area, and new small blood vessels grow into it. This early repair tissue is often described as scar tissue. At first it is weaker than the tissue it replaces, and its fibres are laid down in a fairly random pattern rather than in neat parallel lines.

A longer stage of strengthening and adapting

Over a much longer period, the new tissue is gradually reorganised. Fibres that line up with the direction of everyday pulls are reinforced, while others are broken down and replaced. The tissue becomes stronger and better organised, and it adapts to the loads it is regularly asked to carry. This is why the gradual return of normal movement and activity is part of the usual picture of repair: tissue responds to the demands placed on it. Even so, repaired tissue may not end up quite the same as it was before the injury.

Why repair takes time and varies

OrthoInfo notes that sprains, strains, bruises, tendinitis and bursitis may require a long time to heal, even with appropriate treatment. Several reasons are commonly given. Tendons and ligaments have a thin blood supply, so the raw materials for repair arrive slowly. A larger tear leaves more to bridge. Age, general health, sleep and the demands of work and daily life all play a part. And an injured area that is loaded too hard too soon can be set back, while one that is not used at all can become stiff and weak.

This variation is one reason why estimates of how long an injury will take are best left to a health care provider or physical therapist who has examined it.

Returning to activity gradually

Because repair is a gradual process, a return to sport or heavy work is usually gradual too. MedlinePlus notes that, after the first stage of care for a sprain or strain, later care might include exercise and physical therapy. For anything beyond a minor knock, that return is best planned with a professional who knows the injury, who can judge when the tissue is ready for more and when an injury needs a different kind of care altogether.

When an injury needs checking

A soft-tissue injury is worth having checked if you cannot bear weight or use the limb, if a joint looks misshapen or feels unstable, if there is numbness or weakness, or if pain and swelling are severe or are not settling. The When to see a doctor page lists the signs that need prompt attention, and the sprains and strains page explains the common injuries in more detail.