Locomotor resilience through load-dependent modulation of muscle co-contraction

Area of Science:

• Biomechanics
• Animal locomotion
• Insect physiology

Background:

• Terrestrial locomotion requires adaptation to environmental changes, such as varying slopes.
• Insect slope adjustments are often studied in steady states, neglecting dynamic transitions.
• Previous work showed stick insects alter muscle activity significantly on slopes with minor kinematic changes.

Purpose of the Study:

• To investigate the transition dynamics of slope adjustments in stick insects.
• To determine if compensation for load distribution changes involves distinct steps or a graded process.
• To analyze how Carausius morosus negotiates step-changes in substrate slope.

Main Methods:

• Simultaneous recording of whole-body kinematics and hindleg muscle activity.
• Observation of stick insects (Carausius morosus) during free walking on changing slopes.
• Analysis of muscle activity patterns in response to slope changes and destabilizing events.

Main Results:

• Muscle activity adjusted in a graded manner relative to body pitch during slope transitions.
• Transient adjustments in muscle activity occurred in response to leg lift-off events.
• Antagonist muscle co-activation decreased during specific crawling episodes.

Conclusions:

• Stick insects exhibit graded, not step-by-step, adjustments to load distribution changes.
• Load-dependent regulation of antagonist muscle co-contraction suggests stiffness control.
• The findings indicate a joint stiffness regulation strategy for adapting to load distribution shifts.