Therapeutic Photobiomodulation Before Strenuous Exercise Attenuates Shoulder Muscle Fatigue

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.

Keywords: isokinetic; near-infrared; skeletal muscle.

Figure 1

Flowchart demonstrating the timeline for the study. Participants received a 72-hour recovery between familiarization training and the start of phase 1 and between phases 1 and 2. All participants completed both phases of the study. Abbreviation: PBM photobiomodulation.

Figure 2

Normalized peak torque (NPT) for the 3 blocks of exercise. During the third block of exercise (sets 9–12), participants produced higher levels of NPT after receiving active phototherapy compared with sham phototherapy. ^a Difference (P ≤ .01).

Figure 3

Average torque (AT) for the 3 blocks of exercise. During the third block of exercise (sets 9–12), participants produced higher levels of AT after receiving active phototherapy compared with sham phototherapy. ^a Difference (P ≤ .01).

Figure 4

Total work (TW) for the 3 blocks of exercise. During the third block of exercise (sets 9–12), participants produced more TW after receiving active phototherapy compared with sham phototherapy. ^a Difference (P ≤ .002).

Figure 5

Average power (AP) for the 3 blocks of exercise. During the third block of exercise (sets 9–12), participants produced more AP after receiving active phototherapy compared with sham phototherapy. ^a Difference (P = .001).