Spring or string: does tendon elastic action influence wing muscle mechanics in bat flight?

Area of Science:

• Biomechanics
• Animal locomotion
• Bioengineering

Background:

• Tendon springs are vital for terrestrial locomotion but their role in fluid environments and small mammals remains unclear.
• Understanding these mechanisms can reveal novel insights into biological movement and energy efficiency.

Purpose of the Study:

• To investigate the function of tendon springs in the elbow extensor muscle of a small fruit bat during flight.
• To quantify the contribution of elastic energy storage and recoil in bat wing kinematics.

Main Methods:

• Muscle, tendon, and joint mechanics were measured in a small fruit bat during ascending flight.
• Analysis focused on the elbow extensor muscle's response during wing downstroke and upstroke.

Main Results:

• The tendon stretched during elbow flexion at the end of downstroke, storing elastic energy.
• Tendon recoil during upstroke extended the elbow, aiding in wing unfurling for the subsequent downstroke.
• The tendon spring reduced muscle fascicle strain magnitude by 22.5% compared to a non-elastic system.

Conclusions:

• Tendon elastic action is demonstrated in a small flying mammal, confirming its role in locomotion.
• Series elastic actuator mechanisms are important in fluid-based locomotion, particularly in small-bodied animals.