Does your introductory physics laboratory experiment that analyzes the human arm as a lever assume an inflexible wrist? If so, the analysis of the biceps force required to perform a biceps curl will lead to results that contradict experience: one does not expect the required biceps force to decrease as the mass is raised. We will show that allowing for wrist flexion leads to agreement with empirical data: that the required force does increase as the mass is raised if the wrist angle is allowed to be optimal.
Laing, William B. III; Johnson, Austin; Gonzalez, Albert D.; and Hansen, Chris S., "Including Wrist Flexion in the Human Arm Model Changes Everything!" (2017). Faculty Works. 20.