Someone recently raised a question regarding numbness and weakness resulting from a low back pain episode. He recently had a low back injury from squatting and reaching down to pick up an object. After performing extension exercises according to the McKenzie principles his back pain has completely resolved within 8 to 9 days, but the numbness and weakness have persisted. Then he was told to perform hamstring and piriformis stretches... "Should I do them?" he asked.
It is true that numbness may take some time to resolve, or it may never resolve if scar tissue is adhered to the nerve (unless you stretch it right). Unlike numbness, weakness however can be an indication that the motor nerve is still being interfered, unless it is from disuse atrophy. His injury occurred when he was squatting down and bending forward, and thus extensions (bending back) may likely be the most effective in resolving the rest of the problems. But if he performs hamstrings and piriformis stretches at this time--note that they are both bending forward movements--his problem may be worsened, or a potential relapse would be underway.
It is crucial to know the directional preference of a mechanical derangement according to the symptom behaviors
This is, sadly, a very common phenomenon: clinicians prescibing exercises indiscriminately and patient's progress becomes very inconsistent. In order to allow soft tissues to heal and to elimiate relapse, all forward movements should be avoided--e.g. bending over, slouching, etc. It is crucial to know the directional preference of a mechanical derangement according to the symptom behaviors, and thereby perform the specific targeting reductive exercise.
In this case, it is adviceable for the patient to perform extensions in standing hourly, and also try to perform press up with exhalation in the back extended position (when you come up on your hands) for more reductive pressure. Once he has no more weakness, gained full range in the back, no pain or stiffness for 2 weeks, he can begin stretches that require forward bending in mid-day before and after repeated entensions are performed.
When you do the right thing and proceed carefully, it only takes a couple of weeks to get rid of this kind of problems for good!