The hamstrings are tendons which attach the large muscles at the back of the thigh to the bone. They are very large muscle groups that actually pull on these tendons. The word hamstring originates from the word Hamm, an old English word for the thigh, and string for the cable or string like properties of the tendons which are located above the back of the knee.
The hamstring muscles are also commonly known as posterior thigh muscles and their function is that of bending the knee and also to extend and straighten the hip. They are not used very much in activities such as walking or standing, but are used extensively during running and jumping (also climbing). Athletes and sports people often have very well developed hamstring muscles unlike people who lead more sedentary lifestyles.
Hamstring injuries rarely require surgery, they are usually caused by rapid acceleration such as suddenly starting running and therefore tend to affect footballers, rugby players and athletes who practice running and jumping activities.
Like many other sports injuries hamstring a injury is graded from 1 to 3. A grade 1 injury would be a strain, no tearing of soft tissue, relatively mild pain symptoms and will heal quite quickly. Grade 2 injury would be accompanied by higher levels of pain would be a partial rupture of the tendons and longer rehabilitation time and a grade 3 hamstring injury would be a complete tear of the tendons, be extremely painful and take a lot longer to recover from, sometimes several months and a lot of physiotherapy.
When hamstring injury does occur, quite often a popping sensation is felt and or heard by the sufferer, accompanied by pain and difficulty in walking or even standing if it is a severe injury. Swelling and bruising will often follow, along with tenderness and limping. Obviously immediate cessation of the sports activity and rest, along with painkillers such as ibuprofen, aspirin or a stronger anti inflammatory medication is usually prescribed and the usual RICE strategy of rest, ice, compression and elevation but only in the most severe cases will any form of surgery be needed.
After this a gradual program of stretching and exercise will help to prevent the atrophying effects of immobilization and scar tissue. This would be implemented within a few days of the injury, but a return to the sports activity would not be recommended for several weeks as re injury often happens as a result and would mean a much longer period of recovery and the possibility of a more serious tear that can even lead to a permanent injury.
As soon as the pain and swelling have reduced, gentle and controlled physiotherapy is definitely the way to go to gradually increase strength and flexibility in the damaged tissue but it will often take several weeks or even months depending on how bad the damage was to begin with. Full mobility and being ready to return to the sports activity depends on how bad the hamstring injury was to start with and the individuals willingness to stick to the gradual stretching and physio program.
Here is a link to a video where Premier League Physiotherapist Neal Reynolds talks about the recovery time and rehabilitation of hamstring strain injuries.