A novel "dynamic ligament" smart material that exhibits a strongly rate-dependent response in extension is developed and characterized. The devices, based on elastomeric polymers and shear thickening fluids, exhibit low resistance to extension at rates below 10 mm/s, but when stretched at 100 mm/s or higher resist with up to 7x. higher force. A link between the shear thickening fluid's rheology and the dynamic ligament's tensile performance is presented to explain the rate-dependent response. Future recommendations for improving device performance are presented, along with a host of different potential application areas including safety equipment, adaptive braces, sporting goods, and military equipment.