Is it a Sprain or a Strain? (part 2)

Find out the specifics of sprains and strains in this 2-part article

Part 2: Strains

There is a plethora of information surrounding sprains and strains. As a result, the information presented here has been split into 2 articles. This is part 2 – be sure to check out Part 1: Sprains.

What is a Strain?

When a muscle, tendon (what attaches muscles to bones), or its associated fascia is torn or suffers a stretching-based injury, it is called a strain. A tendon’s collagen fibers, which are what allow the tendon to become taut when its muscle pulls on it, break after a 6%-8% increase in length. However, a tendon is usually twice as strong as its associated muscle, so when a musculotendinous unit is strained, the injury is usually located within the center of the muscle (referred to as the muscle belly) or at the spot where the muscle fibers blend into the tendon (called the musculotendinous junction).

Causes of Strains

Strains are commonly caused by:

• an abnormal muscle contraction that results in the muscle producing more force than its fibers can handle or 
• excessive tension within the fibers resulting from stretching the musculotendinous unit beyond its normal range of motion.

Repeated microtrauma – tiny cellular damage to the tendon without it technically being classified as an injury – can lead to a chronic strain. This actually causes resorption of the collagen fibers. Remember, collagen fibers give the tendons their ability to stretch without injury. So when these fibers are resorbed by the body during chronic injury, the tendon is weakened and made more susceptible to traumatic injury (like a rupture of the tendon).

Like sprains, strains are categorized into 3 degrees of severity. However, unlike sprains, the severity of strains is not judged based on laxity in the joint, but rather on the functionality of the injured musculotendinous unit. Academically speaking, the more severe the strain, the more extensive the damage to the muscle’s fibers.

Classification of Strains

With grade 1 strains, some of the muscle or tendon fibers have been stretched to the point of damage or they have actually torn. The spot that has the tissue damage is tender when pressed and muscle contraction (especially against resistance) is painful. However, the muscle can usually still go through its full normal range of motion.

A grade 2 strain is a more severe injury than a grade 1 strain wherein more tissue fibers have been torn. There is usually a noticeable depression or divot over the site of the injury (you may not be able to see it, but you can certainly feel it – the area feels “squishy” by comparison to the way the rest of the uninjured muscle fibers feel). There may be swelling and bruising, and using the muscle can be extremely painful. In fact, this pain usually limits active range of motion (the amount that the joint moved by that muscle can move without any external help). The perceived flexibility of muscles with grade 2 strains is significantly restricted, too.

A grade 3 strain is a rupture of the muscle or tendon affected. These injuries are extremely painful at first, but the pain actually goes away rather quickly. This is because the nerves near the injury site that send pain signals to the brain are also torn and they no longer send signals to the brain. There is a very obvious defect in the muscle and this defect can be seen in most cases. There is considerable swelling and bruising along with total loss of movement.

The Comparison

So, after all this, what are the similarities and differences between sprains and strains?

The similarities
Strains and sprains are stretching or tearing injuries that occur when the body is forced beyond its normal range of motion.

The severity of strains and sprains is identified by a 3-tiered grading system.

The differences
Tissue type:
Strains are injuries to muscles and tendons.
Sprains are injuries to ligaments and joint capsules.

Criteria for grading severity:
Strains are graded based on the level of dysfunction of the injured muscle/tendon.
Sprains are graded based on the amount of laxity in the joint resulting from the injury to the ligament.