The mechanics of multi-joint posture and movement control

Area of Science:

• Biomechanics
• Neuroscience
• Robotics

Background:

• Muscle force-length dependence creates
• spring-like" behavior in single-joint movements.
• This study investigates how this behavior influences multi-joint posture and movement control.

Purpose of the Study:

• To rigorously define and experimentally test "spring-like" behavior in biological systems.
• To explore the role of inter-muscular feedback in modulating this behavior.
• To describe the directional properties and dynamic aspects (impedance, mobility) of multi-joint systems.

Main Methods:

• Formulating a numerically quantifiable test for "spring-like" behavior.
• Analyzing steady-state force-displacement relationships.
• Investigating synergistic coactivation of polyarticular muscles.
• Introducing mechanical impedance and mobility for dynamic analysis.

Main Results:

• Non-spring-like behavior is attributed to inter-muscular feedback, not intrinsic muscle properties.
• Directional properties of spring-like behavior in multi-joint systems are described.
• Synergistic muscle coactivation modulates these directional properties.
• Apparent inertial behavior of multi-joint systems can be modulated by joint repositioning.

Conclusions:

• The concept of a "virtual trajectory" unifies posture and movement descriptions for multi-joint systems.
• This framework simplifies computational challenges in multi-joint motion control.
• Understanding spring-like mechanics is key to neuro-muscular control and coordination.