Method: Young males without signs or symptoms of musculoskeletal pain were included. Primary outcome measure was the LTR intensities determined by percentage change of muscle thickness. The secondary outcome measures were the muscle elasticity of medial gastrocnemius and hamstring, previous and posterior DN in both lower limbs for each subject. Three LTRs, detected by a physical therapist and ultrasound assessment, were induced by inserting a filament needle into muscle latent trigger points in medial gastrocnemius. The intensities of LTRs were measured by assessing ultrasound images using an optical flow method and through comparisons with manual detection.