How are Muscle injuries Classified

Muscle injuries are common in sports and can result in significant time lost out of training and competition. It can be confusing to know what type of muscle injury you have sustained and what that can mean for time needed to fully recover. Here we try to discuss the British Athletic Classification of muscle injuries to help simplify the differences between muscle injuries and what that can mean for recovery.

If you are around running or sport long enough you or someone you know will have a muscle injury. It may be self-reported or diagnosed by a health professional as a ‘pulled muscle’, ‘torn muscle’ or ‘muscle strain’. These are all umbrella terms that can describe muscle injuries of differing severity, yet are all essentially synonymous. It is common to hear in clinic phrases like ‘I don’t think its bad, I’ve just pulled it but I don’t think it’s a tear.’  So if you have pulled, strained or torn a muscle these are all injuries to the muscle (and/or tendon) with one not being better or worse than another. What these terms don’t describe is the degree of muscle injury, its location or size of the tear. These are all very important factors that are used to grade the severity of injury and influence time to return to full function.

Previous classification of injuries was previously based around clinical or radiographic evidence of muscle injury and graded as either minor, moderate or complete injuries. This was built upon by a Munich consensus statement which expanded its classification to include functional injuries (fatigue induced, DOMS, neuromuscular dysfunction) or structural injuries (tears of different severity). Due to the oversimplification of this classification and some limitations in the terminology a subsequent system was developed. This is the British athletics muscle injury classification. It has 5 grades of injury; grade 0 – through to grade 4. Grade 1 to 4 is further subcategorised into a, b or c, based upon the site and extent of injury.

Grade 0 Injuries

In the British Athletics Classification system grade 0 injuries are classified as: 0a—a focal neuromuscular injury, or 0b—generalised muscle soreness. Both have a normal MRI and typically present as muscle soreness after exercises. 0a injureis are focal soreness after exercise, where Grade 0b represents generalised muscle soreness, which most commonly occurs after unaccustomed exercise, often with an eccentric bias and is frequently termed DOMS. The recovery of these injuries are quite short and the athlete can often continues with minimal change to training routines.

Grade 1 injuries

Grade 1 injuries are small injuries (tears) to the muscle. The athlete will usually present with pain during or after activity. The athlete’s range of movement at 24 h will usually be normal and although there may be pain on contraction, strength and initiation of contraction may be well maintained on clinical examination.  Grade 1a injuries extend from the fascia and demonstrate high signal change on MRI within the periphery of the muscle, no greater than 10% into the muscle and with a longitudinal length of less than 5 cm within the muscle. Grade 1b injuries are sited within the muscle or, more commonly, at the musculotendinous junction. This is the location at which the muscle merges into the tendon. In Grade 1b high signal change is evident at this site and extends over a limited area of less than 5 cm and less than 10% of the muscle cross-sectional area at its maximal site. Frank muscle fibre disruption is not usually seen in this grade of injury. Grade 1 injuries are relatively quick to rehabilitate depending on the muscle group involved and the athletes sport.

Grade 2 injuries

Grade 2 injuries are moderate injuries (tears) to the muscle. The athlete will usually present with pain during activity which necessitates them to stop activity. The range of movement of the affected limb at 24 h will usually show some limitation with pain on initiation of contraction, usually with detectable weakness by a clinician. Grade 2a injuries usually extend from the peripheral fascia into the muscle. Clinical experience suggests that they may be associated with a clinical history of pain during change of direction and manual strength testing may be less reduced with grade 2a injuries relative to other grade 2 injuries. On MRI, high signal change will be evident from the periphery of the muscle and will measure between 10% and 50% of the cross-sectional area of that individual muscle at the site of injury or extend between 5 and 15 cm within the muscle. Grade 2b are similar yet occur at the musculotendinous junction (MTJ). Grade 2c injuries extend into the tendon but injury within the tendon is evident over a longitudinal length of less than 5 cm and less than 50% of the maximal tendon diameter on axial images.

Grade 3 injuries

Grade 3 injuries are extensive tears to the muscle. The athlete will usually present with sudden onset pain and may fall to the ground. They cannot continue activity. Their range of movement at 24 h is usually significantly reduced with pain on walking. There is usually obvious weakness in contraction, swelling and bruising. Grades 3a (myofascial) and 3b (muscular/musculotendinous) will demonstrate MRI features of high signal change patterns of greater than 50% of the muscle cross-sectional area or greater than 15 cm in length. There will be evidence of architectural fibre disruption which is likely to be greater than 5 cm. Grades 3a and 3b are differentiated by the location extending to the periphery (3a) or being within the muscle/at the MTJ (3b). Grade 3c (intratendinous) injuries have evidence of injury in the tendon over a longitudinal length of greater than 5 cm or greater than 50% of the tendon’s maximal cross-sectional area. There is no evidence of a complete defect.

Grade 4 injuries

Grade 4 injuries are complete tears to either the muscle (grade 4) or tendon (grade 4c). The athlete will experience sudden onset pain and significant and immediate limitation to activity. A palpable gap will often be felt. There may be less pain on contraction than with a grade 3 injury, yet are not able to generate any or minimal force.

Return To Sport

Return to full training will occur when the athlete has progressed through a series of appropriate exercise progressions including strength, neuromuscular control, drills, progressive running speeds and passed specific clinical tests. There is evidence from different sports that tendon involvement in muscle injury increases time to return to sport (RTS) and re-injury. As a guide, for hamstring injuries RTS grade 3c (large intradendious tears) can take 8-16weeks, where as 2b tears can take 4-8 weeks, whereas 1a tears could return to sport within 1-3 weeks. A large number of factors other than the grade of tear will determine how quickly an athlete can RTS. These may include:

• Injury history
• Age
• Training history
• Baseline strength and physical fitness
• The demands of the sport
• Recovery (Primarily nutrition and sleep)

Below is a table showing time taken for athletes to return to full training in British Athletics (Runners who had re-injury during rehab are excluded). It illustrates the trend of increasing grade of injury increasing time to return to full training, particularly G3b and G3c. It also shows the substantial increase in reoccurence risk with tendon involvement (c) .  Pollock 2016:

Lewis Craig (APAM)
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Masters of Physiotherapy

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References:

1. Pollock, N., James, S. L., Lee, J. C., & Chakraverty, R. (2014). British athletics muscle injury classification: a new grading system. Br J Sports Med, 48(18), 1347-1351.
2. Macdonald, B., Mcaleer, S., Kelly, S., Chakraverty, R., Johnston, M., & Pollock, N. (2019). Hamstring rehabilitation in elite track and field athletes: applying the British Athletics Muscle Injury Classification in clinical practice. British journal of sports medicine, bjsports-2017.
3. Pollock, N., Patel, A., Chakraverty, J., Suokas, A., James, S. L., & Chakraverty, R. (2016). Time to return to full training is delayed and recurrence rate is higher in intratendinous (‘c’) acute hamstring injury in elite track and field athletes: clinical application of the British Athletics Muscle Injury Classification. Br J Sports Med, 50(5), 305-310.

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