Fatigue Alleviation by Low-Level Laser Pre-Exposure in Ischemic Neuromuscular Electrical Stimulation

Chia-Chan Wu; Yen-Ting Lin; Chia-Ling Hu; Yi-Ching Chen; Ing-Shiou Hwang

doi:10.1249/MSS.0000000000003472

Fatigue Alleviation by Low-Level Laser Pre-Exposure in Ischemic Neuromuscular Electrical Stimulation

Med Sci Sports Exerc. 2024 May 1. doi: 10.1249/MSS.0000000000003472. Online ahead of print.

Authors

Chia-Chan Wu¹, Yen-Ting Lin², Chia-Ling Hu¹, Yi-Ching Chen, Ing-Shiou Hwang

Affiliations

¹ Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan City, TAIWAN.
² Physical Education Office, Asian University, Taichung City, TAIWAN.

PMID: 38689440
DOI: 10.1249/MSS.0000000000003472

Abstract

Purpose: Despite its susceptibility to muscle fatigue, combined neuromuscular electrical stimulation (NMES) and blood flow restriction (BFR) is an effective regimen for managing muscle atrophy when traditional resistance exercises are not feasible. This study investigated the potential of low-level laser therapy (LLLT) in reducing muscle fatigue after the application of combined NMES and BFR.

Methods: Thirty-six healthy adults were divided into control and LLLT groups. The LLLT group received 60 J of 850 nm wavelength LLLT before a training program of combined NMES and BFR of the non-dominant extensor carpi radialis longus (ECRL). The control group followed the same protocol but received sham laser therapy. Assessments included maximal voluntary contraction (MVC), ECRL mechanical properties, and isometric force-tracking for wrist extension.

Results: The LLLT group exhibited a smaller normalized difference in MVC decrement (-4.01 ± 4.88%) than the control group (-23.85 ± 7.12%) (P < .001). The LLLT group demonstrated a smaller decrease in muscle stiffness of the ECRL compared to the control group, characterized by the smaller normalized changes in frequency (P = .002), stiffness (P = .002), and relaxation measures (P = .011) of mechanical oscillation waves. Unlike the control group, the LLLT group exhibited a smaller post-test increase in force fluctuations during force-tracking (P = .014), linked to the predominant recruitment of low-threshold MUs (P < .001) without fatigue-related increases in the discharge variability of high-threshold MUs (P > .05).

Conclusions: LLLT pre-exposure reduces fatigue after combined NMES and BFR, preserving force generation, muscle stiffness, and force scaling. The functional benefits are achieved through fatigue-resistant activation strategies of motor unit recruitment and rate coding.