Training Benefits and Motor Unit Remodeling after Ischemic Neuromuscular Electrical Stimulation with Low-Level Laser Preexposure.

Abstract

Neuromuscular electrical stimulation (NMES) combined with blood flow restriction (BFR) is a promising strategy to prevent muscle atrophy when resistance training is not feasible, though its efficacy may be limited by fatigue. This study examined whether low-level laser therapy (LLLT) can serve as an ergogenic aid during combined NMES-BFR training. Thirty adults were assigned to BFR or BFR + LLLT groups ( n = 15). Both groups underwent a 3-week wrist extension training on the nondominant limb using combined NMES and BFR. The BFR + LLLT group received 60 J of 850 nm laser therapy to the extensor carpi radialis longus (ECRL) before each session; the BFR group received sham treatment. Outcomes included maximal voluntary contraction (MVC) and 40% MVC submaximal force-tracking, with electromyography recorded from the ECRL and extensor carpi radialis brevis (ECRB) muscles. The BFR + LLLT group exhibited a greater posttest/pretest MVC ratio (1.154 ± 0.127) than the control group (1.040 ± 0.058) ( P = 0.004). Although the post-/pretest ratio of force-tracking error did not differ between groups ( P > 0.05), training-related changes in motor unit discharge strategies in the ECRL and ECRB were more pronounced in the BFR + LLLT group. Following training, the BFR + LLLT group exhibited a steeper regression slope between the interspike interval and recruitment threshold in both muscles ( P < 0.001), a pattern that was less evident in the BFR group. In addition, the post-/pretest ratio of the common drive index (CDI) within and between the ECRL and ECRB muscles decreased in the BFR + LLLT group, in contrast to a significant training-related increase observed in the BFR group ( P < 0.001). Pre-exposure to LLLT enhances force output after BFR-NMES training and improves neuromuscular efficiency by increasing motor synergy flexibility, thereby preserving force scaling during submaximal contractions.