Near-infrared light and expectancy effects on maximal isokinetic strength performance: A randomized, double-blind, placebo-controlled study

Infrared-light radiation has recently and effectively been applied to solving a wide range of problems in the sport sciences. However, few investigations have focused on the potential performance-enhancing properties of near-infrared (NIR)-light stimulation, and none have examined its effects on muscle strength. As such, the purpose of this investigation was to determine the extent to which NIR light influenced the maximal isokinetic strength of the quadriceps and hamstrings. Forty-eight college students participated in the study. Four experimental conditions were created: (a) an active group with expectancy instructions, (b) an active group without expectancy instructions, (c) a placebo group with expectancy instructions, and (d) a placebo group without expectancy instructions. Individuals in active conditions were outfitted in NIR light-emitting bandages, T-shirts, and socks, whereas those in placebo conditions were outfitted in the same attire but without active NIR light. Maximal isokinetic torque values of the quadriceps and hamstrings were measured. Results indicated that the active group without expectancy instructions exhibited enhanced isokinetic strength for the hamstrings at a contractile speed of 180°·s^-1 as compared with the placebo groups. With continued replication of our initial exploratory findings, infrared equipment might emerge as a promising means for performance enhancement.