Does a firm mattress help back pain? The evidence points to medium-firm
The old advice to buy the hardest mattress you can find is not what the trials show. A double-blind randomised trial and a systematic review both favour medium firmness.
TENS looked useless in the pooled data until the analysis accounted for intensity
Across 29 studies the overall effect on chronic back pain was not significant. Split by whether the current was strong enough to be clearly felt, one subgroup showed a large effect and the other none.
Exercise beats no treatment for back pain, but only if the small trials stay in
Cochrane found a clinically important 15.2-point pain reduction across 249 trials. A reanalysis excluding trials with fewer than 70 participants put the effect below the threshold that counts as meaningful.
Acupuncture beats no acupuncture by 0.5 SD and sham acupuncture by 0.2
The gap between those two numbers is the whole argument. An individual-patient meta-analysis of 20,827 people found real effects on both comparisons, and found that the choice of sham changed the answer.
Placebo responses in US pain trials grew for two decades. Drug responses did not.
Analgesic trials keep failing, and one reason is that the comparison arm keeps improving. Where a trial recruits, how long it runs and how big it is all move the placebo response — and none of that is about the drug.
551 back pain trials, 71,126 patients, and almost none of it is good evidence
A network meta-analysis found six treatments clearing the clinically important threshold in the short term. It also graded 98.6% of the evidence very low certainty, and found nothing that held up past a year.