Relationship between muscle forces, joint loading and utilization of elastic strain energy in equine locomotion.

The study examines how the horse’s limb muscles and joints bear load and use elastic strain energy during different gaits to help explain the high injury rate at these areas. Evidence shows the muscles and tendons in the forelimb, particularly the superficial digital flexor (SDF) and the interosseus muscle (IM), do the majority of work.

Main Research Objectives

• Research aimed to understand how elastic strain energy utilization and storage contribute to a horse’s efficient movement.
• The study seeks to identify the correlation between dangerously high forces endured by structures facilitating elastic energy storage during different gaits.
• Additionally, it aims to highlight the linkage between muscle forces, joint loading, and the high frequency of injuries identified in specific sites in the equine limb.

Methodology

• The study merged experimental gait data with a musculoskeletal model of a horse’s distal forelimb.
• The focus was on the stance phase of three different gaits: walking, trotting, and galloping.
• The primary variables involved were muscle and joint contact loading and muscle-tendon work during each gait.

Key Findings

• The flexor tendons spanning the metacarpophalangeal (MCP) joint, specifically the superficial digital flexor (SDF), interosseus muscle (IM) and deep digital flexor (DDF), experienced the most significant forces.
• Peak forces normalized to body mass for the SDF were differentiated among walking, trotting, and galloping. The SDF experienced the greatest force during galloping.
• Contact forces transmitted by the MCP joint were higher than those acting at any other joint in the distal forelimb, peaking during galloping.
• Tendons in the distal forelimb, mainly SDF and IM, contributed between 69%-90% of the total work done by the muscles and tendons, varying based on the gait type.
• This study suggests the high load experienced by the tendons and joints that facilitate elastic strain energy storage in the distal forelimb may explain the high frequency of injuries at these sites.