Soleus forces and soleus force potential during unrestrained cat locomotion

Area of Science:

• Biomechanics
• Neuroscience
• Muscle Physiology

Background:

• The soleus muscle's activation level during locomotion is debated.
• Understanding soleus activation is crucial for comprehending force-sharing among ankle extensors.

Purpose of the Study:

• To experimentally determine if the soleus muscle is maximally activated during low-demand walking.
• To investigate the soleus muscle's activation patterns across different walking speeds.

Main Methods:

• Utilized chronically implanted nerve cuff electrodes for supramaximal stimulation of the soleus muscle.
• Measured soleus muscle forces during normal and stimulated walking cycles using a tendon force transducer.
• Tested walking speeds of 0.4, 0.8, and 1.2 m/s.

Main Results:

• Soleus forces increased with supramaximal stimulation during swing and mid-stance phases for slow and intermediate walking speeds.
• For fast walking, force increases were only observed during the swing phase.
• No significant force increases were achieved during early or late stance phases across all speeds.
• Peak forces and initial force increase rates post-paw contact were not substantially enhanced.

Conclusions:

• Soleus muscle force production is maximal throughout the stance phase during fast walking (1.2 m/s).
• For slower walking speeds (0.4 and 0.8 m/s), soleus force is maximal for substantial portions of the stance phase.
• Findings provide insights into force-sharing mechanisms among cat ankle extensor muscles and soleus in vivo properties.