Laser and LED light therapy (photobiomodulation) showed some effect over placebo on time to exhaustion, repetitions, isometric peak torque and blood lactate in healthy people, at very low to moderate certainty, in a review of 39 randomised trials (861 participants), 28 of them pooled; the abstract gives no effect sizes, and its dose ranges (655-950 nm; 20-60 J for small and 60-300 J for large muscle groups) describe where positive trials clustered, not a tested optimum

Vanin, Leal-Junior and colleagues set out to establish whether phototherapy (low-level laser therapy, light-emitting diode therapy or both) improves muscular performance and reduces muscular fatigue in healthy people, when in an exercise protocol it should be applied, and which light parameters work.

They searched five databases to March 2017 for randomised trials, assessed risk of bias and quality of evidence, and contacted authors for missing details. Of 39 included trials (861 participants), 28 entered meta-analyses against placebo for time to exhaustion, number of repetitions, isometric peak torque and blood lactate.

The authors report some effect in favour of phototherapy on these outcomes, at a quality of evidence from very low to moderate, and call for further research because of weak methods, small samples and the variety of exercise protocols and light settings.

Describing the trials rather than pooling them, they note that positive results came with lasers, LEDs or both at 655-950 nm, mostly with 20-60 J for small muscle groups, 60-300 J for large ones and up to 200 mW per diode.