Kiyono, R, Onuma, R, Yasaka, K, Sato, S, Yahata, K, and Nakamura, M. Effects of 5-week foam rolling intervention on range of motion and muscle stiffness. J Strength Cond Res XX(X): 000–000, 2020—In clinical and sports settings, foam rolling (FR) intervention is widely used to increase the range of motion (ROM). But, the chronic effects of FR on ROM and muscle stiffness are unclear. This study aimed to investigate the effects of 5-weeks FR intervention on dorsiflexion ROM (DFROM) and shear elastic modulus of the medial gastrocnemius (MG) muscle. Accordingly, 30 healthy young adults were enrolled and randomly assigned to either the FR or control group with the former receiving 90 seconds of FR thrice per week over 5-weeks. Thereafter, DFROM, passive torque at DFROM, and shear elastic modulus of the MG during passive ankle dorsiflexion were assessed using a dynamometer and ultrasonography before and after 5-weeks. Our results showed that the FR group exhibited a significant increase in DFROM (Δ = 11.7%, p < 0.05, effect size = 0.39), but no changes in passive torque at DFROM, and shear elastic modulus at 0° and 10° dorsiflexion. Moreover, significant correlations were observed between change in DFROM and change in passive torque at DFROM in the FR group (rs = 0.607; p = 0.016). These results suggested that FR was an effective method to increase DFROM given its ability to change passive torque at DFROM (stretch tolerance) without altering muscle stiffness.