"Avatar", a Modified Ex vivo Work Loop Experiments Using In vivo Strain and Activation

Area of Science:

• Biomechanics
• Muscle Physiology
• Neuroscience

Background:

• Movement behaviors emerge from complex neural and mechanical system interactions.
• Understanding neural control strategies and intrinsic muscle mechanics is crucial for accurate muscle force prediction.
• In vivo muscle mechanics are influenced by abrupt changes in strain and loading during locomotion.

Purpose of the Study:

• To investigate muscle function during rapid strain rate and loading changes.
• To determine conditions under which neural control shifts towards intrinsic muscle mechanics ('preflexes').
• To enhance the accuracy of in vivo muscle force and work predictions using improved muscle models.

Main Methods:

• Modification of the traditional work-loop approach into the 'avatar' technique.
• Utilizing measured in vivo strain trajectories and electromyographic (EMG) signals from dynamic movements.
• Driving ex vivo muscles through stretch-shortening cycles using scaled in vivo data on a servo motor.

Main Results:

• The 'avatar' technique successfully emulates in vivo strain, activation, stride frequency, and work-loop patterns.
• The method allows for precise matching of in vivo force responses by varying dynamic patterns.
• Specific features of strain and activation can be manipulated to test mechanistic hypotheses.

Conclusions:

• The 'avatar' technique provides a novel approach to study ex vivo muscle mechanics under in vivo-like conditions.
• This method facilitates a deeper understanding of how muscles function during dynamic locomotion.
• The findings contribute to more accurate predictive models of muscle force and work output.