Equilibrium is an essential concept in undergraduate physics curriculum as it integrates Newton's laws and torque. The importance also comes from its wide applications in mechanics and biomechanics. Simulations of Back and Arms are developed mainly for the undergraduates who major in physical therapy and health sciences. They are implemented as open-ended inquiry learning on the subject of key concepts in equilibrium. Students practice and apply the knowledge to calculate the forces on the erector spinae muscle and lumbar vertebrae, then conclude the optimal posture for lifting a heavy object. Besides enhancing understanding of the lecture materials, students can practice lab skills such as image analysis and control variables.