Muscle Co-Contraction of the Forearm Is Increased in Response to Temporal Uncertainty During a Dynamic Stabilization Task

Modulation of joint stiffness through selective co-contraction of antagonist muscles is integral to adaptive motor control, vital for both feedforward modelling of environmental demands as well as adaptation to proprioceptive feedback. Here, we challenged healthy individuals to stabilize the position of a mechanized wrist exoskeleton under both temporally predictable and temporally uncertain perturbation schedules. The impact of this dynamic stabilization task was then assessed through subsequent cued voluntary flexion and extension movements. Participants demonstrated significantly increased muscular co-contraction in response to uncertain scheduling that remained stable over repeated task exposures. This increased co-contraction was correlated with a delay in reaction time when cued to voluntary movement following the dynamic stabilization task. These results highlight the significant impact of temporal uncertainty on muscle co-contraction and demonstrate how the existing motor context influences subsequent movement.Clinical Relevance - Developing insight into joint stiffness modulation and the role of muscle co-contraction in healthy motor control helps to better understand the deficiencies in these processes present in clinical conditions such as Parkinson's disease (PD). Focusing this understanding on wrist movement is specifically relevant due to clinical assessments of PD commonly utilizing passive mobilization of the wrist as a central assessment of clinical rigidity. As such, understanding how different dynamics modulate wrist stiffness can guide the improvement of current clinical techniques and potentially inspire new diagnostic and therapeutic approaches.