Clinical library · Modalities
Electrotherapy and Passive Modalities
What the evidence supports, what it does not, and what has never been properly tested. Written for clinicians, and readable by anyone who has been offered a machine and told it will fix something.
The short version. Several of these modalities do reduce pain, and saying otherwise would be as inaccurate as overselling them. What almost none of them demonstrate is a lasting change in function, disability or the course of a condition.
That distinction — pain during and immediately after treatment versus outcomes that persist — is the single most useful thing on this page. A machine that reliably makes the next twenty minutes more comfortable can be worth using. It is not a course of treatment.
Why this page exists. Every condition guide on this site carries a row reading "electrotherapy — not tested here", meaning the sources cited on that page did not evaluate it. That is honest but unhelpful if it is all we ever say. This page evaluates these modalities directly, so the answer exists somewhere on the site rather than nowhere.
How to read this page
Three questions are asked of every modality, and they are not the same question:
- Does it reduce pain while it is being applied? Often yes. This is the easiest effect to demonstrate and the least durable.
- Does it improve function, disability or quality of life? Much more rarely, and usually not clearly.
- Does it add anything to an active programme? This is the question that matters clinically, because exercise is the comparator that actually competes.
Watch also for a pattern that appears twice below: the effect shrinks as study quality rises. When low-quality trials find a benefit and high-quality trials find none, the honest reading is that the benefit is probably an artefact of the weaker studies.
What the evidence shows, modality by modality
| Modality | What was found | Verdict |
|---|---|---|
| TENS transcutaneous electrical nerve stimulation |
Pain intensity lower during or immediately after TENS than placebo — SMD -0.96 (95% CI -1.14 to -0.78) from 91 RCTs and 4,841 participants, moderate certainty. Also lower than pharmacological and non-pharmacological standard care (SMD -0.72, 95% CI -0.95 to -0.50), low certainty. [1] | Supported for short-term pain The largest review here: 381 RCTs, 24,532 participants. Effect not modified by risk of bias, sample size, or acute versus chronic pain [1] |
| NMES neuromuscular electrical stimulation, after ACL surgery |
Added to rehabilitation, better quadriceps strength recovery than standard physiotherapy alone at ≤6 weeks (SMD 0.53, 95% CI 0.27 to 0.79) and >6 weeks (SMD 0.59, 95% CI 0.18 to 0.99). Starting within one week did far better than later (SMD 1.48 versus 0.44). [4] | Supported, specific use The strongest case on this page — but for strength after ACL surgery, not for pain, and Lysholm knee scores showed no significant difference [4] |
| Shockwave extracorporeal shockwave therapy |
From level I studies: may be effective alone in plantar fasciitis, lateral epicondylitis and proximal hamstring tendinopathy, and as an adjunct to exercise in medial tibial stress syndrome and osteitis pubis. Athletes generally continued training and tolerated it with minimal side effects. [5] | Promising, condition-specific Of 56 studies only 18 were level I; 25 were level IV or V. The authors call for further high-level research to define its role [5] |
| Therapeutic ultrasound neck pain |
Versus sham or no treatment, significantly reduced pain intensity (5 studies, 256 patients). Added to other treatments, gave additional pain benefit but with high heterogeneity and no clear conclusion, and no better effect on disability or quality of life (7 studies, 449 patients). [2] | Beats sham; unclear it adds anything 12 RCTs, 705 patients, varying quality and high heterogeneity. Safe — no adverse events reported. A large, methodologically valid trial is still needed [2] |
| Mechanical traction lumbar radiculopathy |
Supine traction added to physiotherapy improved pain (g = -0.58, 95% CI -0.87 to -0.29) and disability (g = -0.78, 95% CI -1.45 to -0.11) — but those meta-analyses pooled low-quality studies. Analyses of high-quality studies of prone traction were not significant. [3] | Effect tracks study quality Short-term only, up to 3 months. The quality gradient is the finding: benefit in weak studies, none in strong ones [3] |
| Interferential therapy, laser, diathermy, cryotherapy, thermotherapy | Not evaluated in the reviews cited on this page. | Not covered here This page makes no claim either way. They are on the list for their own entries rather than being lumped in by association |
What this means in practice
TENS deserves better than its reputation — and less than its marketing
The largest piece of evidence on this page is the meta-TENS study: 381 randomised trials and 24,532 participants. It found moderate-certainty evidence that pain intensity is lower during or immediately after TENS compared with placebo, without serious adverse events. [1] Notably, the effect was not modified by risk of bias, sample size, or whether the pain was acute or chronic — which is unusual and argues against the finding being an artefact of weak studies. [1]
Two caveats keep this in proportion. The comparison with standard care was low-certainty, downgraded because small trials made the magnitude imprecise. [1] And the outcome is pain during or immediately after application. That is a real effect and a legitimate use — symptom relief that lets someone move, sleep or tolerate exercise. It is not evidence that a course of TENS changes the trajectory of a condition.
NMES is the one with a genuine mechanism and a genuine indication
After ACL surgery the quadriceps shuts down, and rebuilding it is the central problem of the early phase. Adding NMES to rehabilitation produced better strength recovery than standard physiotherapy alone at both short and long follow-up, and starting within the first week was substantially better than starting later — SMD 1.48 against 0.44. [4]
Note what it did not do: knee function on the Lysholm score showed no significant difference between groups. [4] So the honest claim is "helps restore quadriceps strength early after ACL surgery", not "improves knee outcomes". Used for that purpose, at that time, it has the clearest supporting evidence here.
Traction shows the quality gradient plainly
This is the most instructive entry on the page for anyone appraising evidence. Pooling low-quality studies, supine mechanical traction added to physiotherapy improved pain and disability in lumbar radiculopathy. Pooling high-quality studies of prone mechanical traction, the effects were not significant. [3]
Eight studies met inclusion and only five could be meta-analysed, with benefits confined to three months. [3] When the better-designed trials find less than the weaker ones, the prudent interpretation is that the treatment effect is smaller than it first appears — not that we should quote the more flattering subgroup.
Ultrasound beats sham but may add nothing to real treatment
For neck pain, therapeutic ultrasound significantly reduced pain compared with sham or no treatment. Added on top of other treatments, it produced additional pain benefit but with heterogeneity high enough that the reviewers declined to draw a conclusion, and it did not improve disability or quality of life. [2]
That combination — better than nothing, unclear whether better than what you are already doing — describes a lot of passive treatment. It is safe, with no adverse events reported across 12 trials and 705 patients. [2] Safety is not the same as usefulness.
Shockwave is promising where it is promising, and unproven elsewhere
The evidence is condition-specific rather than general. Level I studies support it alone in plantar fasciitis, lateral epicondylitis and proximal hamstring tendinopathy, and as an adjunct to exercise in medial tibial stress syndrome and osteitis pubis. [5] Of 56 included studies, though, only 18 were level I and 25 were level IV or V — case series and expert opinion. [5]
Read a shockwave recommendation by asking which condition it is for. Support for plantar fasciitis is not support for shoulder pain.
What the evidence supports — and what it does not
Supported
- TENS for short-term pain relief — moderate certainty versus placebo, from 381 RCTs, without serious adverse events. [1]
- NMES for quadriceps strength after ACL surgery, especially started within the first week. [4]
- Shockwave in named conditions — plantar fasciitis, lateral epicondylitis, proximal hamstring tendinopathy. [5]
- Ultrasound as better than sham for pain, and as a safe treatment. [2]
- Using passive modalities to enable activity rather than to replace it.
Not supported
- Any of these as a course of treatment in themselves. The demonstrated effects are on short-term pain, not on the course of a condition.
- Ultrasound for disability or quality of life when added to other treatment. [2]
- Prone mechanical traction — not significant in the high-quality studies. [3]
- NMES as a way to improve knee function scores — no significant difference on Lysholm. [4]
- Generalising shockwave from the conditions where it was tested to those where it was not. [5]
- Quoting the low-quality subgroup when the high-quality one is null. [3]
How certain is this?
Evidence grade: Moderate, and uneven between modalities.
The TENS evidence is the most substantial here by a wide margin — 381 randomised trials — and its central finding was rated moderate certainty. Its comparison against standard care was low certainty, downgraded for imprecision from small trials. [1] Readers should also note that the lead author declares extensive industry relationships, including with TENS device manufacturers, and was an author on several trials considered for inclusion. That is disclosed in the paper, it does not invalidate a review of this size, and it is the kind of thing this site says out loud rather than leaves for the reader to discover.
The traction and ultrasound reviews are small and heterogeneous — eight studies with five pooled, and twelve trials with 705 patients respectively — and both sets of authors explicitly call for better trials. [2][3] The shockwave review is large in study count but weighted towards low-level evidence. [5] The NMES review is narrow in scope, which is a strength for the specific claim and a limit on any wider one. [4]
The largest gap is that these are five modalities among many, each assessed in one or two conditions. Nothing here supports a general statement about "electrotherapy". The entries for interferential therapy, laser, diathermy and thermal modalities are deliberately blank rather than assumed.
Common questions
Is electrotherapy a waste of time?
No, and the evidence does not support saying so. TENS reduced pain more than placebo across 381 randomised trials on moderate-certainty evidence, [1] and NMES clearly helps rebuild quadriceps strength after ACL surgery. [4] The accurate criticism is narrower: these treatments mostly demonstrate short-term pain relief, and rarely demonstrate improved function or a changed course of a condition.
My physiotherapist uses ultrasound every session. Should they?
It depends what it is for. Ultrasound beat sham for pain in neck pain, and it is safe. [2] But when added to other treatments it did not improve disability or quality of life, and the pain benefit came with heterogeneity too high for a conclusion. [2] If it is helping you tolerate exercise, that is defensible. If it is the treatment, and the exercise is the add-on, the priorities are inverted.
Why does one review say traction works and another says it doesn't?
Because both are in the same review, split by study quality. Supine traction added to physiotherapy improved pain and disability when low-quality studies were pooled; analyses of high-quality studies of prone traction were not significant. [3] When results depend on the quality of the evidence you include, the higher-quality answer is the one to trust.
Is shockwave worth trying for my tendon problem?
Possibly, depending which tendon. Level I evidence supports it alone in plantar fasciitis, lateral epicondylitis and proximal hamstring tendinopathy, and as an adjunct to exercise in medial tibial stress syndrome and osteitis pubis. [5] It was well tolerated, and athletes generally continued training during it. [5] For tendons outside that list, the evidence cited here does not answer the question.
Why doesn't this page cite NICE?
Because we could not retrieve the guideline directly to check it. The NICE recommendations on electrotherapy for low back pain are widely quoted, and quoting them second-hand would be easy — but every source on this site is verified against the original before it is cited, and NICE's website blocks automated retrieval. We would rather have a smaller page that is checkable than a longer one that is not. This will be added when it can be verified properly.
What about interferential, laser, or heat and ice?
Not covered here, and deliberately not lumped in with the modalities that were assessed. None of the reviews cited on this page evaluated them, so this page makes no claim about them in either direction. They are on the list for their own entries.
References
- Johnson MI, Paley CA, Jones G, et al. Efficacy and safety of transcutaneous electrical nerve stimulation (TENS) for acute and chronic pain in adults: a systematic review and meta-analysis of 381 studies (the meta-TENS study). BMJ Open. 2022 Feb 10;12(2):e051073. doi:10.1136/bmjopen-2021-051073 PMID 35144946 Systematic review and meta-analysis of 381 RCTs
- Qing W, Shi X, Zhang Q, et al. Effect of therapeutic ultrasound for neck pain: a systematic review and meta-analysis. Archives of Physical Medicine and Rehabilitation. 2021 Nov;102(11):2219–2230. doi:10.1016/j.apmr.2021.02.009 PMID 33722564 Systematic review and meta-analysis
- Vanti C, Panizzolo A, Turone L, et al. Effectiveness of mechanical traction for lumbar radiculopathy: a systematic review and meta-analysis. Physical Therapy. 2021 Mar 3;101(3):pzaa231. doi:10.1093/ptj/pzaa231 PMID 33382419 Systematic review and meta-analysis
- Li Z, Jin L, Chen Z, et al. Effects of neuromuscular electrical stimulation on quadriceps femoris muscle strength and knee joint function in patients after ACL surgery: a systematic review and meta-analysis of randomized controlled trials. Orthopaedic Journal of Sports Medicine. 2025 Jan;13(1):23259671241275071. doi:10.1177/23259671241275071 PMID 39811154 Systematic review and meta-analysis
- Rhim HC, Shin J, Kang J, et al. Use of extracorporeal shockwave therapies for athletes and physically active individuals: a systematic review. British Journal of Sports Medicine. 2024 Feb 7;58(3):154–163. doi:10.1136/bjsports-2023-107567 PMID 38228375 Systematic review
About this resource
A note on how we write this
We publish what the evidence does not support.
A modality library that only lists what works is marketing. This page states where the effect disappears in better-quality studies, where a treatment beats sham but not real care, and where we could not verify a source well enough to cite it.