Simulations of the Human Body

Simulation of an Upper Limb III

This simulation is analogous to a person holding a ball by side. There are seven forces in the diagram, the joint reaction force on the shoulder, JRF_s and the one on the elbow, JRF_e (black); the force that is exerted by the person's deltoid muscle, F_del and bicep muscle, F_bic (orange), the weight of the upper arm, W_UA, the weight of forearm, W_FA and the weight of ball W_bal (red). As the angle of the upper arm, θ_arm and the exterior angle between the forearm and upper arm, θ_FA change, the simulation provides the approximations of the forces on the joints and muscles at different arm postures. The vector arrows show the differences in the magnitudes and directions of forces. When the weight and the height of the person, W_bal are changing, the arrows also change accordingly.
Notes: The simulation is calculated based on a normally proportioned person.

Objectives:
  1. Find out how JRF_s, JRF_e, F_del and F_bic change with the mass of the ball.
  2. Observe how the forces on joints and muscles change when the arm moves; discover the easiest and most challenging positions for the person when carrying the same load.
  3. Be able to relate the simulations to life experience and explain the results by applying the knowledge of equilibrium.

Instructions:
According to the case you are investigating, you can replace initial values of the masses and height of the person. Similarly, the position of the arm and the weight of ball can be changed with the slider bars. During your exploration, pay attention to control variables.