Photobiomodulation against placebo had small effects on muscular endurance (p = 0.02) and on strength (p = 0.04) in healthy people, in a random-effects meta-analysis of 23 randomised trials; the abstract gives p values but no effect sizes, and the dose and timing findings are exploratory subgroup splits the authors say cannot define a protocol
Main caveat: The authors' own: subgroup findings are exploratory; the evidence cannot define optimal protocols.
Zhai and colleagues pooled randomised trials that compared photobiomodulation with a placebo on quantitative measures of muscle performance in healthy people, and looked for sources of variation in participants and light parameters. They searched six databases to November 2025, rated risk of bias with Cochrane RoB 2 and pooled 23 trials with a random-effects model.
The light had small effects on muscle endurance and on muscle strength. Most subgroup differences were not significant; the endurance benefit reached p = 0.05 in athletes and p = 0.07 in physically active people.
Settings that went with endurance benefits were 100 mW or less per diode, 31-100 J, application 1-3 min before exercise and four or fewer sites; strength went with 151-300 J and an interval over 3 min.
The authors conclude that the light may modestly improve endurance and strength, more for endurance, that the subgroup findings are exploratory, and that the evidence cannot yet define an optimal protocol.
Participants
23 randomised trials in healthy humans; subgroups of athletes and physically active people are named; numbers, ages, sex and sports are not in the abstract.
Protocol
Search: PubMed, CENTRAL, Scopus, Medline, EBSCOhost and Web of Science, inception to November 2025.
Inclusion: randomised trials of photobiomodulation against placebo with quantitative muscle-performance outcomes in healthy people; two reviewers screened and extracted independently.
What was applied: photobiomodulation delivered through diodes at one or more sites, before exercise in at least the trials behind the timing subgroups (1-3 min or more than 3 min beforehand); the abstract does not say whether the devices were lasers, LEDs or both, which muscles were treated, whether the device touched the skin, or the wavelengths.Dose bands named in the abstract are 31-100 J and 151-300 J (other bands, and whether any went higher, are not given); power per diode split at 100 mW.
Outcomes: muscle endurance and muscle strength (specific tests not in the abstract).
Risk of bias: Cochrane RoB 2; the result is not in the abstract.
Analysis: random-effects model; subgroup analyses by participant characteristics and light parameters.
Key Results
| Outcome or subgroup (light vs placebo) | Result in the abstract |
|---|---|
| Muscle endurance, all trials | small effect, p = 0.02 |
| Muscle strength, all trials | small effect, p = 0.04 |
| Endurance, athletes | p = 0.05 (reported as a benefit) |
| Endurance, physically active people | p = 0.07 (reported as no benefit) |
| Endurance, ≤100 mW per diode | p = 0.03 |
| Endurance, 31-100 J | p = 0.05 |
| Endurance, applied 1-3 min before exercise | p = 0.03 |
| Endurance, ≤4 application sites | p = 0.007 |
| Strength, 151-300 J | p = 0.05 |
| Strength, interval over 3 min | p = 0.007 |
Most tests of subgroup differences were not significant (the authors); effect sizes, intervals and heterogeneity are not in the abstract.
Our reading: each subgroup p value appears to test the effect within that subgroup against zero, so "athletes 0.05, physically active 0.07" is not a shown difference between the two.
Practical Application
Photobiomodulation (device type and body sites not in the abstract) gave small gains in muscular endurance and strength over placebo across 23 randomised trials in healthy people, more for endurance; the abstract gives no effect sizes, and the authors say the evidence cannot yet define a protocol.
Do not prescribe the subgroup settings: 31-100 J, 100 mW or less per diode, four or fewer sites and 1-3 min before exercise went with endurance benefits, but the tests of subgroup differences were mostly not significant and these are comparisons between trials. Strength went with a different dose (151-300 J) and a longer interval (over 3 min), which fits chance findings across many between-trial splits (our reading).
Inference, not tested here: the trials applied the light through diodes at a counted number of sites on the body; the results say nothing about a room lamp or a whole-body bed.
Under SYNTH-83: "tested; small gains on muscular endurance and strength, settings not established", not "it works" and not "a myth".
Limitations
The authors' own: subgroup findings are exploratory; the evidence cannot define optimal protocols; more and better-designed trials are needed to standardise the light parameters.
No effect sizes, intervals, heterogeneity, participant numbers or risk-of-bias results in the abstract.
Many subgroup tests on 23 trials; several "favourable" settings sit at p = 0.05, and no correction for multiple tests is mentioned.
Funding and conflicts of interest are not in the abstract. Written from the abstract and the PubMed record; full text not read.
How this entry was checked and changed
Why this level
a meta-analysis of randomised trials, risk of bias not read (abstract only)
Content correction 2026-11-11
2026-11-11: added from the abstract and the PubMed record; level B+ (meta-analysis of randomised trials, risk of bias not read).