Hamstring “tightness” is something we’ve all felt, we’ve all heard of, and we’ve all tried to solve. The hamstrings are an important muscle group that has a lot of function. It crosses both the hip and knee joint, so understandably you would expect them to get “tight.” We’ve also all heard about how my chronically “tight” hamstrings are causing my knee pain, hip pain, back pain, etc. Riddle me this: Someone has “tight” hamstrings, stretches diligently every day for a month, they come back to see you and their 90-90 hamstring test is exactly the same. What gives? Nerve tension is what gives. Nerve tension is more common than most people think, and most people aren’t even aware of it. Today I’m going to talk about what nerve tension is, how to decipher if you have “tight” hamstrings or tension sensitivity in the nerve, and how to address either or both.
What is true hamstring “tightness?” I keep using quotation marks for the word tight, because I wrote a blog about my hatred for that word and why is it useless (here). True hamstring tightness simply means your hamstring muscles are shorter than they should be. The actual muscle cell (sarcomere) is not as long as some of the muscle cells elsewhere. You can address this by consistent static stretching. Consistency will lengthen the hamstrings and decrease the sensitivity to the stretch, thus improving your hamstring muscle length.
Nerve tension is increased longitudinal force on a given nerve potentially restricting its movement through the foramina. In this case we are talking about the sciatic nerve and where is starts at the lumbar and sacral nerve roots, as well as the sheath surrounding the nervous tissue. Nervous tissue contains elastin, which is a molecule that allows the tissue to be stretched without disrupting its function. However, the amount of elastin in nervous tissue is much smaller compared to arteries and organs such as the heart and lungs. Given the limited amount of elasticity in the nervous tissue, increased stretch will irritate the nerve. The irritation can cause physical changes (i.e. inflammation) and chemical changes (i.e. disruption of ion flow balance) which produces a sensation of “tightness” in your hamstrings. The sciatic nerve runs on a similar path to the hamstrings and if you stretch the hamstrings incorrectly, you actually increase the stretch on the already irritated sciatic nerve.
How do you determine if you have nerve tension or hamstring length issues? The slump test is used to determine the extent of your nerve tension sensitivity. It has been well established that certain leg movements produce stretch on the nervous tissue (Goddard 1965, Coppieters 2006). To perform the slump test, follow these steps:
Sit on a bench with your feet not touching the floor
Slouch at your lower back
Bring your chin all the way down to your chest
Dorsiflex your ankle (bring your toes up)
****SLOWLY**** - straighten your knee until you feel a stretch in the hamstring, calf, or pull in the low back.
Once you feel that pull/stretch/sensation, make a mental note of how far your knee was from straightening
Repeat on the opposite leg and compare
Normal is within 20 degrees from full knee extension before you feel any pulling. If you don’t have that amount of motion, but both sides are the same then you just have to keep an eye on nerve tension. If you don’t have that amount of motion on one side, but do on the other, then you have nerve tension. This tension is likely the cause of your hamstring “tightness.” To determine if you have short hamstrings, perform the 90-90 active extension test.
Lie on your back with one leg held in 90 degrees of hip flexion. Actively extend your knee and note how close you get to straight. Normal length is 70 degrees (meaning 20 degrees from completely straight). If you have less, then you have short hamstrings and would benefit from stretching. Do the 90-90 test AFTER you have done the slump test. If both are positive, you cannot stretch your hamstrings as that will be exacerbating your nerve tension.
So how do you solve your hamstring length or nerve tension problems? If you have hamstring length issues, but do not have nerve tension then statically stretching your hamstrings will do the trick. Make sure you stretch them appropriately so you don’t cause nerve tension!
If you have nerve tension, then you simply need to avoid positions that put you into nerve tension. There are 3 very common tasks/positions that replicate nerve tension: driving, sitting on the couch watching TV with your feet on the coffee table (being reclined is different and does not count), and stretching your hamstrings. Some things to be cautious with are RDLs, box deadlifts, seated hamstring curls. Essentially if your leg gets straighter than where you started to feel the pull during the slump test, then that movement or task needs to be adjusted. Avoidance of nerve tension is the easiest way to get rid of it. You may have heard about nerve flossing. Nerve flossing is a way to move the nerve through the foramina (where it exits the spine). Goddard and Coppieters examined excursion and found that the sciatic nerve can move up to 10mm through its foramina. If the nerve becomes adhered to the bone (scar tissue from surgery or significant trauma), then nerve flossing is indicated to restore the normal movement as explained by Goddard and Coppieters. If the nerve is not adhered, then nerve flossing will cause the sciatic nerve to exceed the normal amount of movement. The increased mobility of the sciatic nerve provides minimal benefit with an extremely high amount of risk. Consistently adding and removing tension through nerve flossing techniques is a great way to irritate the nerve to the point where you now have a positive slump test. If you are feeling pulling sensations during movements, then the smart choice is to evaluate the movement to see where you can improve rather than try a cool nerve flossing technique and give yourself real problems. Let’s take the RDL as an example. If I complete an RDL with my knee completely extended, then I feel a pull right behind my knee joint. The sciatic nerve is being stretched over my ankle joint (since it runs behind my ankle joint), over my knee joint (since it runs behind my knee joint), and over my hip joint (since it runs behind my hip joint). If I simply bend my knee just a tiny bit (think unlocking the knee or athletic stance) then all of the tension added from my knee joint is eliminated and the movement should feel normal (a slight stretch in the middle of the hamstrings towards the bottom of the move).
Thanks for reading about nerve tension and hamstring “tightness.” Stretch your hamstrings when appropriate and watch out for nerve tension positions through your workouts and everyday life. If you have any questions, leave them in the comments below!
References
Coppieters, M., Alshami, A., Babri, A., Souvlis, T., Kippers, V., & Hodges, P. (2006). Strain and excursion of the sciatic, tibial, and plantar nerves during a modified straight leg raising test. Journal of Orthopaedic Research, 24(9), 1883-1889.
Goddard, M., & Reid, J. (1965). Movements induced by straight leg raising in the lumbo-sacral roots, nerves and plexus, and in the intrapelvic section of the sciatic nerve. Journal of Neurology, Neurosurgery, and Psychiatry, 28(1), 12-18.