In this study, the characteristics of muscle relaxation were analyzed by the experimental and numerical method. A skin tissue was produced by imitational biological tissue using the agar powder, saline solution and sugar. The tissue was exposed to three types of wavelength-blue visible radiation(410 nm), red visible radiation(635 nm), and infrared ray(830 nm). The temperature results along the depth of tissue were measured according to the variation of light wavelength and irradiation time. The temperature change of the tissue shown up similar pattern regardless of the light wavelength kinds. The wavelength of infrared ray penetrated strongly into tissue between 3.2 mm and 11.4 mm. Also, the temperature change with the irradiation time was small, and the temperature value of the infrared ray was the largest. As a result, the muscle relaxation will occur mainly at the infrared wavelength.

Despite research to treat delayed onset muscle soreness (DOMS), no effective treatment has been reported. The purpose of this study is to investigate the effect of a hold-relax technique and cryotherapy on DOMS. Thirty-three subjects were randomly assigned to one of three treatment groups: control, hold-relax technique, or hold-relax technique and cryotherapy. DOMS was induced in the non-dominant biceps muscle through repeated eccentric contractions. Resting elbow joint position, flexion and extension (universal goniometer), pain (Visual Analogue Scale; VAS), and WBC count (blood analysis) were measured one hour before DOMS was induced and 24, 48, and 72 hours after DOMS was induced. The data were analyzed by repeated measure of two-way ANOVA. The results of this study were summarized as follows: 1) While analysis showed no significant differences between groups in relation to a resting elbow joint position, there were significant differences over time, especially at 24, 48 hours after DOMS was induced compared with resting elbow joint position before DOMS was induced. 2) While analysis showed no significant differences between groups in relation to range of flexion, there were significant differences between range of flexion before DOMS was induced and range of flexion 72 hours after DOMS was induced. 3) There were no significant differences between groups or over time in relation to range of extension. 4) While analysis showed no significant differences between groups in relation to VAS, there were significant differences over time in different hours. 5) There were no significant differences between groups or over time in relation to WBC count. 6) There were no interactions between groups or over time in all variables. This results suggested that hold-relax technique and cryotherapy were not effective to reduce DOMS.