Abstract
CONTEXT: Photobiomodulation therapy (PBMT) applied as a preconditioning treatment before exercise has been shown to attenuate fatigue and improve skeletal muscle contractile function during high-intensity resistance exercise. Practical implications for preconditioning muscles with PBMT before fatiguing exercise include a safe and noninvasive means to enhance performance and reduce the risk of musculoskeletal injury. OBJECTIVE: To examine the muscle fatigue-attenuating effects of PBMT on performance of the shoulder external-rotator muscle group when applied as a preconditioning treatment before high-intensity, high-volume resistance exercise. DESIGN: Sham-controlled, crossover design. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty healthy men (n = 8) and women (n = 12) between the ages of 18 and 30 years. INTERVENTION(S): Photobiomodulation therapy was administered using a near-infrared laser (λ = 810/980 N·m, 1.8 W/cm2, treatment area = 80-120 cm2) to the shoulder external-rotator muscles at a radiant exposure of 10 J/cm2. Participants performed 12 sets of isokinetic shoulder exercise. Each set consisted of 21 concentric contractions of internal and external rotation at 60°/s. The sets were subdivided into 3 blocks of exercise (block 1: sets 1-4; block 2: sets 5-8; block 3: sets 9-12). MAIN OUTCOME MEASURE(S): Normalized peak torque (N·m/kg), average peak torque (N·m), total work (N·m), and average power (W). RESULTS: During the last block of exercise (sets 9-12), all performance measures for the active PBMT condition were 6.2% to 10% greater than the sham PBMT values (P < .02 to P < .001). CONCLUSIONS: Photobiomodulation therapy attenuated fatigue and improved muscular performance of the shoulder external rotators in the latter stages of strenuous resistance exercise.