I would have to agree with Wendy, that pain is a warning sign, whether it be an early sign in acute injury or a late sign of something more insideous.
TENS does nothing more than to confuse the nervous system & brain into thinking that the pain stimulus isn't there & may in some cases reduce some of the muscle spasm. The latter being the more useful, although still doesn't address the underlying cause.
This symptomatic relief may be valid i.e. in the case of giving birth, but low back pain during & after pregancy should not need to be tolerated & an osteopath should be able to help with treatment and advice in most cases.
With regular use & over time TENS tends to become less effective, whilst the underlying problem has become a chronic (long term) condition, which typically are more difficult to treat and recover from.
Suggest taking a look in the Back Pain Forum under Ailments for some of the possibilities of back pain. [sm=scratchchin.gif]
Andrew.