Low-Level Laser Therapy Facilitates Post-Contraction Recovery with Ischemic Preconditioning.

Abstract

Despite early development of muscle fatigue, ischemic preconditioning is gaining popularity for strength training combined with low-load resistance exercise. This study investigated the effect of low-level laser (LLL) on post-contraction recovery with ischemic preconditioning. Forty healthy adults (22.9 ± 3.5 years) were allocated into sham (11 males, 9 females) and LLL (11 males, 9 females) groups. With ischemic preconditioning, they were trained with three bouts of intermittent wrist extension of 40% maximal voluntary contraction (MVC). During the recovery period, the LLL group received low-level laser (wavelength of 808 nm, 60 Joules) on the working muscle, whereas the sham group received no sham therapy. MVC, force fluctuations, and discharge variables of motor units (MU) for a trapezoidal contraction were compared between groups at baseline (T0), post-contraction (T1), and after-recovery (T2). At T2, the LLL group exhibited a higher normalized MVC (T2/T0) (86.22 ± 12.59%) than that of the sham group (71.70 ± 13.56%)(p = .001). The LLL group had smaller normalized force fluctuations (LLL: 94.76 ± 21.95%, Sham: 121.37 ± 29.02%, p = .002) with greater normalized EMG amplitude (LLL: 94.33 ± 14.69%, Sham: 73.57 ± 14.94%, p < .001) during trapezoidal contraction. In the LLL group, the smaller force fluctuations were associated with lower coefficients of variation of inter-spike intervals of MUs (LLL: .202 ± .053, Sham: .208 ± .048, p = .004) with higher recruitment thresholds (LLL: 11.61 ± 12.68 %MVC, Sham: 10.27 ± 12.73 %MVC, p = .003). Low-level laser expedites post-contraction recovery with ischemic preconditioning, manifesting as superior force generation capacity and force precision control for activation of MUs with a higher recruitment threshold and lower discharge variability.