Forelimb muscle activity during equine locomotion.

The research focuses on the activity of the horse’s forelimb muscles during movement. It reveals a new understanding of the roles each muscle plays in different types of equine locomotion such as walking, trotting, and cantering.

Research Methods

• In order to better understand the functionalities of forelimb muscles, the researchers measured the timing and amplitude of the electromyographic (EMG) activity of these muscles. EMG is a technique for recording and analyzing the electrical activity produced by muscles.
• The researchers conducted these measurements in relation to different forms of locomotion — walking, trotting, and cantering — and the different demands these forms of movement placed on the joints of the horse’s forelimbs.
• They also compared the amplitudes of muscle activation with the net joint torques to discover if passive structures, like ligaments and tendons, also play significant roles in torque generation (the turning or twisting force on an object).

Research Findings

• The research found that all the forelimb muscles, with the exception of the extensor carpi radialis (ECR) muscle, were activated just before the hoof struck the ground and deactivated during the stance phase.
• The unique activity of the ECR was that it was activated during the swinging or movement phase and not prior to contact with the ground like the other muscles.
• The intensity of muscle activation, evidenced by the amplitudes recorded, increased with the speed of the gait. Yet, the researchers found that the muscle activation amplitudes were not proportional to the net joint torques. This suggests that other passive structures play a substantial part in producing movement forces.
• Smaller distal muscles — those further away from the center of the body — help to stabilize the forelimb in preparation for the stretching of passive structures. These smaller muscles remained active throughout the stance phase in a canter when the torque acting on the distal forelimb joints was highest.
• The findings suggested that the larger, proximal muscles — those closer to the center of the body — activate to position and stabilize the shoulder and elbow joints during ground contact in a complex coordination of muscle activity.