Classification according to Peetrons8
| Grade 0 | Lack of any lesion using MRI* or US, despite clinical diagnosis of posterior thigh muscle injury. |
| Grade 1 | Minimal elongations with less than 5% of the muscle involved. |
| Grade 2 | Partial muscle ruptures. They correspond to lesions involving from 5% to 50% of the muscle volume or cross-sectional diameter. |
| Grade 3 | Complete muscle tears with complete retraction. Usually, these lesions are clinically evident because the muscle belly forms a real mass and because a gap can be palpated between the retracted ends of the muscle. |
↵* This classification is originally described for ultrasound; Davis26 described the same classification for MRI.
US, ultrasound.