Force USA Solitude Leg Extension / Leg Curl Machine | Commercial Dual-Function Strength Equipment | Fitness Specialist TXForce USA Solitude Leg Extension Leg Curl Machine The Force USA Solitude Leg Extension Leg Curl Machine is a full commercial grade dual function unit engineered to build and strengthen both the quadriceps and hamstrings in one compact station. With heavy duty construction, smooth biomechanics, and easy adjustment between leg extension and seated leg curl, this machine delivers efficient lower body training that stands up to the demands of busy