Glossary · Biomechanics
Muscle redundancy
Also called redundancy, redundant muscles, actuator redundancy, muscle sharing problem
A body has more muscles than it has ways to move, so many different patterns of muscle effort give the same movement.
A knee mostly bends one way, but more than ten muscles cross it, and several of them cross the hip or the ankle too. For any torque the joints need, there are endless ways to share it between the muscles: more from one, less from another, or more from both sides at once (co-contraction). That is muscle redundancy. A motor-driven robot has one motor per joint and no such choice.
People don’t share the load at random. A common explanation is that the nervous system picks patterns that cost little effort or energy, while keeping enough stiffness to be safe. Simulations of human movement often reproduce this by penalising the sum of squared activations.
In this project
In Muscles instead of motors, stage 2b put the full MyoLeg on the fighter, 80 leg muscles, many of them crossing two joints, and the policy learnt the stance with them. The experiment measured whether and how fast it learnt; which of the many possible patterns it chose, and whether a person would choose the same, was not studied yet.