If you are completing this example as a laboratory exercise for a course on human movement, you will need to submit answers to these questions. These questions can be saved as a Word document by selecting "Export to Word" from the Tools menu in the top-right corner of this page.

B: Explore the contribution of each muscle group to jumping

  1. Briefly describe how exciting each of the muscle groups affects the joint angles (*states_degrees.mot) and the ground reaction forces (*forces.sto) of the simulation:
    1. VAS
    2. SOL
    3. GAS
    4. GMAXM and GMAXL
    5. HAMS
    6. ADM
  2. Why do forces in VAS, which are uniarticular knee extensors, accelerate joints they do not span? Explain this dynamic coupling both physically and in terms of the inertia matrix of Eq. (1).

C: Jump sky high

  1. Report your best performance numbers:
    1. Ligament penalty
    2. Jump height
    3. Overall performance (Jump height + Ligament penalty)
  2. If you are able to get the model to jump anywhere near the jump height predicted by the optimal solution (i.e., over 0.37 m), you should be congratulated! In the more likely event that your solution was not as high as the optimal solution, explain why.
  3. Report your second-best performance numbers:
    1. Ligament penalty
    2. Jump height
    3. Overall performance
  4. What is the performance difference between your best and second-best jumps? What would you infer is the function of the eliminated muscle during jumping?
  5. Plot the sum of the vertical ground reaction force (foot_r.calcn_r.force.Y, foot_r.toes_r.force.Y, foot_l.calcn_l.force.Y, foot_l.toes_l.force.Y in Jumper_ForceReporter_forces.sto) normalized by body weight predicted by your solution and by the optimal solution. The mass of the model is 75.1658 kg, and the acceleration due to gravity is assumed to be 9.80665 m/s2. The vertical ground reaction force (Fy) for the optimal solution is in the file DynamicJumpCoordination_optimal_ground_reactions.xlsx.
    1. Does your ground reaction force have a higher or lower peak compared to that in the optimal solution?
    2. Is the time to lift-off longer or shorter compared to that in the optimal solution?
  6. Plot the resultant articular contact force at the hip normalized by body weight. (The joint contact forces can be found in Jumper_JointReaction_ReactionLoads.sto)  Why are the hip contact forces so large?
  7. On a plot, superimpose the excitation levels, activation history, and normalized force history predicted by your solution for vas_int_r. To normalize the force predicted by vas_int_r, divide the force by the maximum isometric strength of vas_int_r (6865 N – see Anderson and Pandy, 1999). Include this plot in your report. Given what you know about muscle mechanics, explain why the force generated by vas_int_r was less than its isometric strength.

Reflection

Provide some suggestions for future offerings of the course:

  • Were any elements of this lab confusing? How could they be improved?
  • What resources did you use? Was anything missing or unclear in the OpenSim documentation?
  • What was the best part of this lab? What would you add to improve the lab?