Red light therapy adds no clear strength gain

Photobiomodulation — low-level laser or LED light applied to muscle — is increasingly sold as a way to squeeze more adaptation out of the same training. The pitch is attractive for older adults, who are the group most motivated to defend strength as they age and the group most exposed to expensive add-ons. Individual randomised trials have pointed in different directions, some suggesting a boost and others nothing at all. What was missing was a pooled answer to a narrow, practical question: when light therapy is bolted onto a properly periodised resistance programme, do people end up stronger?

The reviewers searched seven databases, including PubMed, Scopus, Embase, PEDro, Web of Science, the Cochrane Library and CNKI, from inception to January 2026. Eligible studies were randomised controlled trials in older adults using low-level laser therapy or light-emitting diodes alongside resistance training or other strength-oriented loading. Eleven RCTs with 456 participants met the inclusion criteria. Prespecified meta-analysis was restricted to the five trials that combined photobiomodulation with periodised resistance training and reported one-repetition maximum outcomes, giving 74 participants in the light-therapy arms and 72 in controls; the remaining studies were described narratively.

On the primary outcome, maximal strength, photobiomodulation plus resistance training was not significantly better than sham photobiomodulation plus the same training (SMD 0.26, 95% CI -0.08 to 0.59; p = 0.14), with low heterogeneity between trials (I2 = 4%). Subgroup analysis showed a non-significant trend favouring light therapy for unilateral one-repetition maximum tests and no effect for bilateral tests, with no significant difference between subgroups. Sensitivity analyses showed that even the unilateral trend depended on individual studies rather than being a stable signal. Outside resistance-training contexts, some studies reported possible benefits for fatigue, recovery or function, particularly in frail or critically ill older adults, but findings were inconsistent.

This is the first pooled attempt to settle a literature the authors describe as inconsistent, and it lands on the unglamorous side: the confidence interval crosses zero, so the honest reading is that no clear additional benefit has been demonstrated. Low heterogeneity means the trials broadly agreed with each other rather than cancelling out, which strengthens the null somewhat. It does not prove that light therapy does nothing, because the pooled sample is small and a modest effect would be hard to detect. Open questions remain about wavelength, dose, timing relative to sessions, and whether recovery-related outcomes rather than raw strength are where any value lies.

If you are choosing where to spend effort or money on getting stronger later in life, the evidence currently sits with the training itself rather than the light. The pooled result is a reason to treat claims that photobiomodulation amplifies strength adaptations as unproven rather than established. Anyone already using a device is not doing something shown to be harmful — no benefit is not the same as harm — but there is no strength-based reason to expect it to be doing much. The authors themselves call for larger, better-designed trials before any role is settled.