What to know about a hamstring strain comes down to understanding just what the hamstring is, how it can become injured and what can be done to treat it. If the strain is treated with the proper level of seriousness, the injury can heal relatively quickly and normal activities such as walking, running and jumping can commence soon after the injury.

A strain to the hamstring muscle is the most common leg injury, and stories of a strain to some favored football or baseball player (or any athlete who makes great use of his or her legs) are legion. In fact, athletes of all ages and abilities will at one time or another experience a strain of varying degrees of severity. Usually, the injury is relatively minor in scope.

There are three levels of severity of strain when it concerns the hamstring; Grade 1, Grade 2 and Grade 3. Those people who feel a twinge or stab of pain at the back of the thigh -- and when the pain isn't particularly severe or only occurs when vigorous walking or running occurs -- are said to have suffered Grade 1 and 2 injuries. They aren't particularly severe but can become so if immediate treatment isn't undertaken.

For those people who experience sharp, stabbing pain that refuses to go away, noticeable bruising at the back of the leg and an inability to walk using that leg, it is fairly certain that they've experienced a Grade 3 injury, which medical professionals consider a severe event that requires immediate treatment in order to limit its severity.

Often, a Grade 3 injury that involves a strain that has led to a tear or rupture of the muscle will need to be surgically repaired. Additionally, a full physical therapy treatment regimen will be implemented in order to return the repaired hamstring back to optimal function and full range of motion.

At least initially all three grades of strain and injury will call for the same basic treatment, which is known by its acronym, "RICE." Standing for Rest, Ice, Compression and Elevation, RICE is an effective tool to help an injured person overcome his or her muscle injury. Immediately after the strain, rest the leg in an elevated position for up to 5 days. Apply ice packs to the injured area for 20 minutes every two hours, especially during the first 48 to 72 hours.

Those who have a Grade 1 injury of light severity can often return to full activity after only 3 days of treatment. Full recovery, though, normally takes up to 3 weeks. Grade 2 injuries can require up to 6 weeks and Grade 3 injuries -- after repair -- could take up to 12 weeks of recovery and physical therapy.