Hamstrings are unusual in that they pass over two joints, the hip and the knee. They are therefore most likely to be injured when the hip is bent and the knee fully straightened. Further stretching may cause an injury that varies from a strain to a classic rip.
Although the hamstrings run down the back of the thigh, injury to the lower part may well be felt behind the knee, either on the inside or outside.
Not only may there be pain behind the knee, but, depending on whether the muscle sheath higher up the thigh is breached, there may or may not be visible tracking of blood down the thigh.
While the knee is bent and the area is not under pressure, there may appear to be little wrong. Straightening the knee and stretching the hamstrings, however, should show all the classic signs of a hamstring injury.
Are probably not necessary unless the condition, as may happen with hamstring injuries, fails to resolve.
What else could it be?
A bursa around the hamstring insertions, a Bakers cyst or ligament strains may all cause pain in roughly the same site. Careful examination should eliminate these.
Following the 48 hours of obligatory RICE, any bleeding should have died down and you can start to stretch. If it's painful still, see Hamstring tears.
Combining the use of ice and educated stretching with interferential physiotherapy or ultrasound should bring about a complete cure.
Can you run through it?/ Recovery time
This sort of minor hamstring tear ought not to bother a runner for more than three or four weeks and the more obsessive among us will find ways of limping through training that may be of doubtful value.
You feel sudden pain when the muscle is over-stretched for example, when hurdling an obstacle or sprinting at the end of a race. It then hurts when you straighten the knee, and running will be slow, if not impossible.
The professional can usually put a finger on the site of a tear and induce appropriate discomfort. There may be a gap within the muscle, or hardened bruising, but it is encouraging if there is visible bleeding under the skin and tracking of the blood flow towards the knee. This indicates that the sheath of muscle has been breached, blood has escaped and healing will therefore be more rapid. Pain occurs if bending the knee is resisted, or if the patient attempts to stretch the muscle.
What else could it be?
Damage to the sciatic nerve by a lumbar disc is a well-recognised red herring which causes pain in the back of the thigh. The doctor will also wish to exclude those infections, tumours and bone and muscle disease which strike these areas once in his professional lifetime.
You cannot go wrong with RICE, always remembering that this should be continued through rehabilitation, as the muscle is stretched and power is regained. Not only is the commonest cause of hamstring injury an unrehabilitated prior tear, but a weak hamstring muscle also predisposes to knee injury.
Can you run through it?/Recovery time
Recovery time may be days, weeks or months, depending on the severity of the tear and how rapidly you treat it. Running through it is unwise, but that is unlikely to stop the masochists among you.