Stabilizing stiffness is the most limiting factor in human force exertion

Humans have a remarkable ability to manage physical interaction despite a complex musculoskeletal system, slow muscles and substantial neural delays. Most physical interaction tasks require force generation, and that can be influenced by body configuration and task stability. In this work we investigate the human limits of force generation with respect to these factors. We devised an experiment in which healthy individuals performed a maximum voluntary pushing task using a custom-designed gimbal apparatus which allowed us to change the ability to transmit torque at the wrist. The experiment was repeated in two different arm positions to assess the effect of limb configuration. The results showed a substantial decrease in maximum force with less wrist ability to generate stabilizing stiffness, and minimal difference in maximum pushing force between the two arm configurations. Our findings confirm our hypothesis that stiffness production appears to be a prominent factor limiting force exertion. The limits of human force exertion remain an open and challenging research question in human biomechanics and motor neuroscience. Here, the authors demonstrate that the ability to generate stabilizing stiffness during force exertion is a key factor limiting performance.