Red light therapy added to strength training did not clearly boost muscle strength in older adults

A systematic review and meta-analysis pooled eleven randomized controlled trials involving 456 older adults to examine whether photobiomodulation—delivered via low-level laser or light-emitting diodes—enhanced strength gains when added to resistance training programs. The pooled result showed no statistically significant improvement in maximal muscle strength compared with sham treatment, though the authors note a small true effect cannot be ruled out.

What the study found

The primary pooled analysis, restricted to five trials that combined photobiomodulation with periodized resistance training and measured one-repetition maximum, returned a standardized mean difference of 0.26 in favor of photobiomodulation—a result that did not reach statistical significance and whose confidence interval crossed zero. The evidence does not support a meaningful additional strength benefit from adding photobiomodulation to a structured resistance program in older adults.

Subgroup analyses separated unilateral from bilateral strength measures. A non-significant trend favored photobiomodulation for unilateral outcomes, while bilateral outcomes showed no effect at all; the difference between these subgroups was itself not statistically significant. Sensitivity analyses further revealed that the unilateral trend depended heavily on the inclusion of individual studies, making it an unreliable signal.

Six trials that did not meet the criteria for the primary meta-analysis—because they used non-periodized loading or did not report one-repetition maximum—were summarized narratively. Within this group, some studies reported possible benefits related to fatigue, physical function, or recovery tolerance, particularly among frail or critically ill older adults, though these findings were inconsistent across studies.

The authors conclude that current evidence does not establish a clear added benefit for maximal strength, while leaving open the possibility that photobiomodulation may have selective value for recovery-related outcomes or for supporting training participation in more vulnerable older populations. They call for larger, more rigorously designed trials to resolve the question.

Limits worth knowing

The meta-analysis was limited to five trials with a combined sample of 146 participants in the pooled analysis, constraining statistical power to detect small effects. All participants were older adults, so findings may not generalize to other age groups. Trials varied in photobiomodulation device type, wavelength, application timing, and training protocols, introducing heterogeneity that the authors attempted to manage through prespecified subgroup restrictions. The narrative synthesis covered a broader but more heterogeneous set of studies, including some involving frail or critically ill individuals, which limits direct comparison. Funding sources for the included trials were not uniformly disclosed in the abstract, and the review itself does not report industry sponsorship. Outcomes beyond maximal strength—such as muscle hypertrophy, quality of life, or long-term adherence—were not the focus of the primary analysis.

About this entry. The Heartwood Review summarizes published, peer-reviewed research in its own words and links to the original source. It is not medical advice; consult a physician before beginning or changing any thermal or recovery practice. Findings summarized here describe the study cited, not any product sold by Teak & Marble Atelier. Corrections.