Andre De Grasse's hamstring strain explained

Canadian sprinter Andre De Grasse's type of hamstring injury is a small tear, sports medicine experts say — but what does that mean?

De Grasse, 22, said he felt a "grab" in his right hamstring during training in London on Monday, his agent Paul Doyle said in a statement. De Grasse flew to Munich where he was diagnosed with a Grade 2 hamstring strain.

"I was told by his coach that it's a Grade 2, so it's moderate in nature," CBC Sports host Perdita Felicien said in an email. "It is a small tear and could have been worse. But serious all the same."

"Hamstrings can be nagging injuries that linger. They can be difficult to heal, [treat] and hard to put behind a runner once sustained," said Felicien. "Sprinters typically train at full effort, so unless the muscle is fully healed you cannot train or even jog effectively. Even when it feels better it may not be; that I know from experience."

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Our hamstring muscles are at the back of the thigh. They're commonly injured among athletes and weekend warriors alike.

Sprinters and football players are particularly susceptible because their sports demand rapid acceleration, said Dr. Ryan Degen, an orthopedic sports medicine surgeon and assistant professor at Western University in London, Ont.

There are three main muscles in the hamstring: the semimembranosus, semitendinosus and biceps femoris.

Doyle's statement said De Grasse's ultrasound scan suggested a strain of the long head of the biceps femoris.

Without seeing the sprinter's MRIs, it's hard to tell the degree of injury, Degen said. Generally, MRI scans of a Grade 2 injury show partial muscle fibre disruption that typically involves less than half of the muscle width, he said.

A Grade 3 injury involves more than half the muscle width.

Recovery process

In the medical literature, Grade 3 injuries are usually associated with a slower return to sport, but there is no correlation with chance of recovery, Degen said.

As long as De Grasse listens to his physicians, he should have a chance of a full recovery with no long-term implications, Degen said.

As with any such injury, there are some issues to keep in mind.

"One big concern is scar tissue," Felicien said. "That thickens within the tissue and causes it to lose its natural elasticity.  Muscles need to stretch and contract freely to have the right amount of tension. An injured muscle is a forever changed muscle and that is the risk."

De Grasse's coach, Stuart McMillan, told reporters in London that the Markham, Ont., sprinter needs "at least a five-to-six-week rehab process."

When CBC Sports analyst Anson Henry spoke with De Grasse Wednesday night after news of the injury was revealed, De Grasse said the final advice he received was, 'Look, if you do this, [run now] you literally could ruin your career.'"

Degen explained that's because any type of athletic competition with a partial injury risks worsening the tear. That could lead to a higher chance of reinjury down the road and a delayed return to sport, he said.