Exposure to an incompatible virtual surgery impacts the null space components of the muscle patterns after re-adaptation but not the task performance *

Under the synergy hypothesis, novel muscle synergies may be required for motor skill learning. We have developed a "virtual surgery" experimental paradigm that alters the mapping of muscle activations onto virtual cursor motion during an isometric reaching task using myoelectric control. By creating virtual surgeries that are "incompatible" with the original synergies, we can investigate learning new muscle synergies in controlled experimental conditions. We have previously shown that participants are able to improve their task performance after an incompatible virtual surgery, using novel muscle patterns to overcome the perturbation. In this work, we investigated whether the activation of novel muscle patterns, that are required after an incompatible virtual surgery, affects task performance or the muscle patterns after re-adaptation to the unperturbed baseline mapping. We found that experiencing an incompatible virtual surgery did not affect the task performance during the baseline mapping. However, the adaptation to the incompatible virtual surgery resulted in changes in the null space components of the muscle patterns used in the unperturbed task.