The Effects of Near-Infrared phototherapy Pre-irradiation on Lower Limb Muscle Strength and Injury Following Exercise: A Systematic Review and Meta-analysis

Objective: Assess near-infrared pre-irradiation effects on post-exercise lower limb muscle damage and function, determine optimal dosage.

Data source: PubMed, EMBASE, Cochrane Library, EBSCO, Web of Science, CNKI (China National Knowledge Infrastructure), and Wanfang Data were systematically searched (2009-2023).

Study selection: Incorporate randomized controlled trials of near-infrared pre-irradiation on lower limb muscles post-fatigue exercise into the meta-analysis. Out of 4550 articles screened, 21 met inclusion criteria.

Data extraction: The included studies' characteristics were independently extracted by 2 authors, with discrepancies resolved through discussion or a third author. Quality assessment utilized the Cochrane risk of bias tool and the GRADE System.

Data synthesis: In 21 studies, near-infrared pre-irradiation on lower limb muscles inhibited the decline in peak torque (SMD: 1.33, 95% CI: 1.08 to 1.59, p < 0.001, Increasing 27.97±4.87NM), reduced blood lactate (SMD: -0.2, 95% CI: -0.37 to -0.03, p = 0.272, decreasing 0.54±0.42mmol/L), decreased creatine kinase (SMD: -2.11, 95% CI: -2.57 to -1.65, p < 0.001, decreasing 160.07±27.96U/L), and reduced delayed-onset muscle soreness (SMD: -0.53, 95% CI: -0.81 to 0.24, p < 0.001). Using a 24-hour cutoff revealed two trends: treatment effectiveness depended on power and energy density, with optimal effects at 24.16 J/cm² and 275 J/cm² for energy, and 36.81 mW/cm² and 5495 mW/cm² for power. Noting that out of 21 studies, 19 are from Brazil, 1 from the U.S., and 1 from Australia and the results exhibit high heterogeneity CONCLUSION: : Although we would have preferred a more geographic dispersion of laboratories our findings indicate that near-infrared pre-irradiation mitigates peak torque decline in lower limb muscles. Influenced by energy and power density with a 24-hour threshold, optimal energy and power densities are observed at 24.16 J/cm², 275 J/cm², 36.81 mW/cm², and 5495 mW/cm² respectively. It also reduces blood lactate, CK, and DOMS.