What is a hamstring injury? How long does it take to recover? What are the grades of injury?

A number of Premier League players – including Arsenal’s Kai Havertz and Chelsea’s Nicolas Jackson – have suffered hamstring injuries in recent weeks. A Grade 2 hamstring strain could be anything from approximately one per cent of the muscle to 95-99 per cent of the muscle, so it’s a very non-precise grading of the significance of the damage. Generally, without using clinical information, imaging or knowing the individual characteristics of the player and their previous injury history, if you took the average length of time it takes for someone to come back from a hamstring injury you’d be quoting around three weeks. In terms of muscle injuries, from a general perspective, you want to introduce lengthening muscle contractions – called ‘eccentric’ muscle contractions, such as the lowering part of a bicep curl or straightening part of a hamstring curl – as soon as possible, because we know that they produce favourable adaptations in terms of the muscle. The hamstring tends to only become a large-force producer at higher speeds of running, so if someone has a hamstring injury you can often get them running fairly early on in the process – the caveat being a complete rupture – but it won’t be until the latter stages of rehab that they’d hit top speeds.