Summary of British Athletics Muscle Injury Classification system
| Grade | Description | MRI |
| 0 | Focal or generalised muscle pain following exercise | Normal or patchy high signal change throughout one or more muscles. |
| 1a | Small myofascial tear | High signal change evident at the fascial border with less than 10% extension into muscle belly |
| Craniocaudal distance of < 5 cm. | ||
| 1b | Small muscular/muscle–tendon junction tear | High signal change of less than 10% cross-sectional area of muscle usually at the muscle-tendon junction |
| High signal change of craniocaudal length <5 cm (may note fibre disruption of <1 cm) | ||
| 2a | Moderate myofascial tear | High signal change evident at fascial border with extension into the muscle |
| High signal change cross-sectional area of between 10% and 50% at maximal site | ||
| High signal change of craniocaudal length >5 cm and <15 cm | ||
| Architectural fibre disruption usually noted over less than 5 cm | ||
| 2b | Moderate muscle–tendon junction tear | High signal change evident within the muscle, usually at the muscle-tendon junction |
| High signal change cross-sectional area of between 10% and 50% at maximal site | ||
| High signal change of craniocaudal length >5 cm and <15 cm | ||
| Architectural fibre disruption usually noted over less than 5 cm | ||
| 2c | Moderate sized intratendinous tear | High signal change extends into the tendon with longitudinal length of tendon involvement <5 cm |
| Cross-sectional area of tendon involvement <50% of maximal tendon cross-sectional area | ||
| No loss of tension or discontinuity within the tendon | ||
| 3a | Extensive myofascial tear | High signal change evident at fascial border with extension into the muscle |
| High signal change cross-sectional area of greater than 50% at maximal site | ||
| High signal change of craniocaudal length of greater than 15 cm | ||
| Architectural fibre disruption usually noted over more than 5 cm | ||
| 3b | Extensive muscle–tendon junction tear | High signal change cross-sectional area of greater than 50% at maximal site |
| High signal change of craniocaudal length of greater than 15 cm | ||
| Architectural fibre disruption usually noted over more than 5 cm | ||
| 3c | Extensive intratendinous tear | High signal change extends into the tendon |
| Longitudinal length of tendon involvement >5 cm | ||
| Cross-sectional area of tendon involvement >50% of maximal tendon cross-sectional area | ||
| There may be loss of tendon tension although no discontinuity is evident | ||
| 4 | Full thickness tear of muscle | Complete discontinuity of the muscle with retraction |
| 4c | Full thickness tear of tendon | Complete discontinuity of the tendon with retraction |
Modified with permission from Pollock et al.11
If any characteristics of a higher grade injury are present the injury is graded at the highest grade.