Force-sharing among the primary cat ankle muscles.
Force-sharing measurements among the cat ankle extensors have been used for the past 20 years to elucidate the mechanisms underlying normal movement control and to study the force-sharing among synergistic muscles. Despite these efforts, many questions have eluded satisfactory explanation. Specifically, there has been great debate to what degree the soleus muscle is activated during low level locomotion, and whether the force-sharing among the ankle extensors is primarily caused by central or peripheral factors. We have measured the forces and corresponding electromyo-graphical activities in the soleus, gastrocnemius, plantaris, and tibialis anterior in more than 20 cats and for a variety of movements. Based on these measurements, and additional information obtained on the structural and functional properties of the cat ankle muscles, we conclude that the peak soleus forces are virtually maximal for all speeds of locomotion, despite an apparent submaximal level of activation at slow speeds. Furthermore, we found that the force-sharing among the soleus and gastrocnemius encompasses the entire possible range; from large soleus forces and zero gastrocnemius forces during still standing, to large gastrocnemius forces and no soleus forces during a high-frequency paw shake. Finally, we support the idea that shifts in force-sharing from one muscle to the other are primarily caused by central factors; the peripheral factors, although appealing when considering the large differences in size, morphology, and fibre type distribution, are likely only of secondary importance.
Herzog
W
W
University of Calgary, Faculty of Kinesiology, AB, Canada. walter@kin.ucalgary.ca
D000818:Animals; D002415:Cats / Q000502:physiology*; D004576:Electromyography; D008124:Locomotion / Q000502:physiology; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D013643:Tarsus, Animal / Q000502:physiology*