Hello Badbackbetsy,
There are a few reasons why muscles will spasm. 1. The muscles are too short, requiring stretching. 2. The body is making the muscles spasm to splint or guard an underlying problem (disk bulge, nerve entrapment, muscle tear or other musculo-skeletal problem. 3. A learned response in the muscle that is no longer relevant to actual physical injury or disability,
All of the above can give the same symptoms, which can be very painful and frustrating.
Treatment requires a good assessment otherwise improvement will not occur. The description of muscle weakness may be misleading. The problem may be causing your body to inhibit the ability of your muscles to provide full strength contractions until you exercise resulting in an excessive splinting reaction for protection of the area ie a spasm.

The TENS like machine inhibits the muscles ability to spasm. A spinal scan would be a good idea if physio techniques are not providing longer lasting improvement. Have you had a second opinion and physical assessment?

Trigger point dry needling (using an acupuncture needle but not acupuncture) can be very effective for this type of problem, especially if the needles are connected to electrical stimulation. Sports taping can also assist.

More information may help me fine tune the suggestions to assist you further.
Cheers,
MrPhysio+