Preferred speeds in terrestrial vertebrates: are they equivalent?

Area of Science:

• Biomechanics
• Animal Locomotion
• Vertebrate Physiology

Background:

• Terrestrial animals exhibit 'preferred speeds' for locomotion, where energy costs are minimized.
• Understanding the mechanical basis of these preferred speeds is crucial for linking energetics to muscle mechanics.

Purpose of the Study:

• To determine if preferred locomotion speeds are mechanically equivalent across species, indicated by similar peak muscle stress.
• To investigate if peak muscle stress at preferred speeds represents a consistent fraction of maximal isometric stress.

Main Methods:

• Comparative analysis of white rats (galloping) and kangaroo rats (hopping) at their preferred speeds.
• Measurement of peak stress in ankle extensor muscles using force platform and cine analysis.
• In situ measurement of maximum isometric force for the same muscle groups.

Main Results:

• White rats and kangaroo rats exhibited nearly identical peak muscle stress at preferred speeds (approx. 70 kPa).
• Peak isometric stress values were also similar between species (approx. 200-206 kPa).
• Preferred speeds correspond to approximately one-third of maximal isometric stress.

Conclusions:

• Preferred locomotion speeds appear to be mechanically equivalent across species, characterized by similar peak muscle stress.
• This suggests muscles are recruited to a similar fraction of their capacity at preferred speeds, maintaining a consistent reserve capacity.
• The findings support a generalizable principle for muscle recruitment and mechanical equivalence in terrestrial vertebrate locomotion.