The anatomy of a muscle tear or strain.
Muscle injuries are the most frequent cause of injury in sports and exercise. It has been estimated that 30 to 50% of all sports-related injuries are caused by muscle related tears and strains.
Here’s a great video on the anatomy of muscle to begin with:
How to muscle tears occur ?
These injuries usually occur when the force exerted by a muscle when is working against an opposing force. This leads to excessive stretching of the muscle fibers and consequently a tear or strain will occur.
Muscle injuries are typically observed in the superficial muscles that work over two joints, such as the thigh muscles, (rectus femoris), hamstrings, (semitendinosus), calf muscle, (gastrocnemius muscles).
Are there different types of muscle strain or tear ?
Muscle tears can be graded by location in the muscle tendon unit and by the severity of the tear.
There are different regions of the muscle tendon unit that can be injured which are shown in this diagram:
- body of the muscle.
- Peripheral fascia into the muscle.
- muscle extending into the tendon.
In 2014 the BJSM published a grading system based on a review by the British Athletics Federation. They divided muscle tear gradings into the following 5 categories which relate to location and severity of injury :
Grade 0 Muscle tear
clinical presentation of focal muscle soreness usually after exercise, although it may also occur during exercise. It is often accompanied with awareness on muscle contraction. There is no damage to the structure of the muscle tendon unit.
Grade 1 Muscle tear
small injuries (tears) to the muscle. Muscle fibre damage is not usually seen in this grade of injury but may extened to about 5cm . Any evidence of fibre disruption of less than 1 cm.
Grade 2 Muscle tear
These are moderate injuries (tears) to the muscle and usually extend from the peripheral fascia into the muscle. The site of injury is between 5 and 15 cm within the muscle. Architectural fibre disruption will be less than 5 cm.
Grade 3 Muscle tear
These are extensive tears to the muscle. Up to 50% of the muscle cross-sectional area or greater than 15 cm in length will be involved. There will be evidence of architectural fibre disruption which is likely to be greater than 5 cm.
Grade 4 Muscle tear
This is a complete tear to the muscle. A palpable gap will often be felt in the muscle and it can involve the tendon as well.
How does a muscle tear heal ?
This video is a good animation on how muscle repairs after trauma. Its the same process whether a sports injury or a snake bite !
The healing of a strain injury follows a fairly constant pattern and can be divided into 3 different overlapping phases:
Stage 1) Destruction phase.
The ruptured muscle fibre or myofibre dies or becomes necrotized over a short distance. Further damage or necrosis of surrounding healthy muscle tissue is halted by a “fire door”. This is a band of connective tissue formed within a couple of hours of injury. This essentially contains the damaged tissue and saves the healthy tissue.
The ruptured myofibers then contract and form a gap between the stumps. This gap is then filled by a blood to form a haematoma. The haematoma will then fibrosis and form the a plug of scar tissue. This injury process also induces a brisk inflammatory response.
Stage 2) Repair phase.
This begins within in 24 hours of injury and starts with the clearing up of the necrotized tissue by cells in a process called phagocytosis. Think of your own little Pac-men munching on the dead tissue.
Then satellite cells that are found in the muscle cells are activated. These are like factories in the cell that help produce new muscle tissue known as myoblasts which are the starting building blocks to form new myotubes which form the new muscle fibres.
These myotubes grow towards the scar formed by the haematoma and anchor into it reforming a continuous muscle fibre.
The injury site is also revascularized by ingrowing capillaries with the first angiogenic capillary sprouts seen three days after the injury. A good blood supply is essential for good healing response.
3) Remodeling phase.
This is the period when the new muscle fibres and scar tissue mature to become a stronger active contractile component. This scar tissue will retract and pull the ends of the new muscle tissue closer to each other. The scar tissue also thins and becomes a thinner connective tissue layer.
They new muscle fibres appear to stay separated by this thin layer of connective tissue to which the ends remain attached by forming new mini Musculo-tendinous Junctions. Similar to what we see when muscle tissue transitions into tendon but at a microscopic scale.
How long does a muscle tear or strain take to heal ?
It depends on a few factors such as grade of injury, injury history and age of the athlete. Quite often people are trying to jump back to action before they are fully fit. As a guide here’s the research on strength returning in elite sprinters following a hamstring tear:
- 70% at 2 weeks post injury
- 85% at 3 weeks post injury
- 90% at 6 weeks post injury
- 100% at up to 16 weeks !!!!
Most re-injury rates occurs around the week 6-8 mark interestingly enough.
So what do i do next if i tear a muscle ?