What causes hamstring injuries? If you read articles on this topic, invariably you will be told that stretching the hamstring muscle beyond its limit can strain or tear the muscle or cause sharp pains, spasms, swelling and bruising. If it hurts to run or if your hamstring is bruised and tender, the diagnosis is overtraining, muscle tightness and fatigue. If you have pain while walking but not running, the diagnosis is possible low back injury. You may also read that inflexible hamstrings limit motion and stress the lower back. If you have knee pain, it may be due to hamstring tightness because the knee has to work harder to perform extension movements.
If these symptoms were indicative of the true causes of injury and if everyone followed the recommendations for fixing them, such as do more stretching and strengthening, the amount of hamstring injuries should decrease greatly. But we do not see this. Instead, we still see many injuries occurring, and, in many cases, more severe than usual. It is rare to find a team with no hamstring problems! Many teams, including professional ball clubs, have even lost great players for most of if not the entire season because of hamstring injuries.
What is missing in these diagnoses, and fixes, is understanding how the hamstrings function in running and cutting. For example, when you drive the knee forward, the hamstring undergoes an eccentric stretch at the hip joint and when the shin whips out, there is a stronger eccentric contraction of the hamstring muscle and its tendons at the knee joint. These eccentric contractions are needed to prepare the hamstrings for the pawback movement, the main force-producing action to drive the leg down and back to make contact with the ground and propel the body forward.
But what happens to the eccentric-concentric contractions at the hip joint and knee joint if the switching of the contractions misfire or the player has incorrect running technique? This has not been studied, but yet I firmly believe that it is in the synchronization of the contractions and joint actions that cause hamstring injuries, due mainly to improper technique.
Constant static stretching of the hamstrings does very little to prevent injury. When you drive the thigh forward, the knee is bent which gives slack at the hip end of the muscle so that you have an ample range of motion. Overstretching creates conditions that do not allow the hamstring to function properly.
In regard to tight hamstrings causing back problems, I have yet to see a player who has such tight hamstrings that he does not have normal curvature of the spine or could not run effectively. If the spine is held in its normal anatomical position while running, the hamstrings cannot be considered too tight and cause the back to flatten. Any back flattening that occurs is when the body is in full support on the ground at which time the hamstring at the hip joint is stretching (hip flexion) and thus, cannot be “too tight.” If you can do a half or three quarter squat while maintaining normal spinal curvature, you do not have excessively tight hamstrings.
Constant static stretching of the hamstrings as many players do is often the cause of many running injuries, especially to the hamstring. Many players are proud of the fact that they can touch their toes when they bend over with straight legs or can raise their leg up onto a rail and then bend over and touch the foot with the fingers. Most of these exercises, because you have a rounded back, overstretch the ligaments of the lumbar spine more than they stretch the hamstring. As a result, you end up with a looser back more prone to injury rather than a safer or stronger back or hamstring muscle.
Muscles need strength with flexibility, thus, instead of doing mainly static stretches, you should do strength exercises that also stretch the muscles and connective tissue in the same exercise. For example, doing the squat exercise stretches the quadriceps and hamstrings eccentrically at the hip joint on the down phase, if you maintain normal curvature of the spine. When you rise up, you strengthen these muscles in the concentric contraction. Thus, you stretch and strengthen in the same exercise. You do not have to go through a greater range of motion for more stretching because it is never encountered in running.
See Explosive Running for more details and exercises specific to the hamstrings and running. Also explained in great detail is how to run effectively and prevent hamstring injury.