Interplay of muscle activation and muscle-tendon decoupling mechanisms during perturbed human gait

• Applicant: Dr. Sebastian Bohm
• Subject Area: Anatomy and Physiology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513866416

Real-world environments rarely allow for stable and constant human locomotion. Most often, the locomotor behavior is characterized by unsteadiness and challenged by different types of external environmental perturbations. When encountering an unpredicted perturbation during locomotion, reactive neuromuscular responses (i.e. preflexes, reflexes and behavioral motor control) allow for rapid alterations in muscle force generation in order to prevent a fall. On the other hand, prior experience of a specific perturbation triggers proactive adjustments in the neuromotor control that regulate the muscle force output in advance, reducing the consequences of the perturbation. Effective compensatory muscle force output is regulated not only by the fast adjustments of the muscle activation but also depends on the operating length and velocity of the muscle due to the intrinsic muscle force-length and force-velocity relationships. Currently very little is known about the underlying mechanisms that regulate favorable operating conditions (high force-length and force-velocity potentials) of muscles during perturbed locomotion. The decoupling of the muscle fiber excursions from that of the muscle belly due to muscle fiber rotation, the decoupling of the muscle belly excursions from that of the muscle-tendon unit (MTU) due to tendon compliance and the force-length-activation dependency are important mechanisms that influence the operating muscle fiber length and velocity conditions. The purpose of the two-year-project is to better understand the integrated function of muscle activation and MTU decoupling mechanisms during perturbed locomotion, which is particularly relevant for real-world conditions. Specifically, we will address (i) how the muscle activation and mechanisms of fiber rotation and tendon compliance decoupling interact and regulate the muscle force potential throughout the different phases of the recovery time course, i.e. preflex, reflex and behavioral control, (ii) how the muscle force level during the perturbation onset influences the contribution of the fiber rotation and tendon compliance decoupling and (iii) how prior experience modulate the interplay between muscle activation and MTU decoupling mechanisms during repeated predictable perturbations. With this project we will provide basic mechanistic insights on how the MTU decoupling and force-length-activation dependency influences and regulates the operating muscle force-length-velocity potentials during perturbed walking. Further, the findings may provide important information for clinical and geriatric contexts in which locomotor abilities are deteriorated or for the design of assistive devices suited for realistic environments.

• DFG Programme: Research Grants
• Co-Investigator: Professor Adamantios Arampatzis, Ph.D.