muscle redundancy does not imply robustness to muscle dysfunction

it is well-known that muscle redundancy grants the cns numerous options to perform a task. does muscle redundancy, however, allow sufficient robustness to compensate for loss or dysfunction of even a single muscle? are all muscles equally redundant? we combined experimental and computational approaches to establish the limits of motor robustness for static force production. in computer-controlled cadaveric index fingers, we find that only a small subset (<5%) of feasible forces is robust to loss of any one muscle. importantly, the loss of certain muscles compromises force production significantly more than others. further computational modeling of a multi-joint, multi-muscle leg demonstrates that this severe lack of robustness generalizes to whole limbs. these results provide a biomechanical basis to begin to explain why redundant motor systems can be vulnerable to even mild neuromuscular pathology.