Whether muscle stiffness is influenced by fatigue remains unclear. Classical methods used to assess muscle stiffness provide a global measure at the joint level. As fatigue may selectively affect specific muscles, a joint-level approach may not be sensitive enough to detect potential changes in muscle stiffness. Taking advantage of ultrasound shear wave elastography, this study aimed to determine the influence of a fatiguing protocol involving intermittent submaximal isometric contractions on muscle shear modulus (an index of stiffness). Shear modulus was measured on either the vastus lateralis (VL; n= 9) or the abductor digiti minimi (ADM; n= 10) before and after 15-mins of intermittent submaximal isometric contractions at 60% of maximal voluntary contraction (MVC; 4 s ON, 4 s OFF). An index of active muscle stiffness was estimated PRE and POST-fatigue as the slope of the linear regression established between shear modulus and absolute joint force up to 60% MVC. After the fatiguing exercise, MVC was significantly decreased by 22±7% and 32±15% for knee extension and little finger abduction, respectively (p< 0.001). When compared to PRE-fatigue, the index of active muscle stiffness was 12±15% lower for the VL (p< 0.031) and 44±19% lower for the ADM (p< 0.001) POST-fatigue. Although the present results cannot clearly determine the involved mechanisms, they demonstrate a decreased active muscle stiffness after a fatiguing task involving intermittent submaximal isometric contractions. Further studies should now determine whether this change in stiffness affects performance and risk of injury.