Fatigue behavior of subchondral bone under simulated physiological loads of equine athletic training.

The study investigates the impact of rigorous physical activity similar to horse racing on fatigue-induced injuries in the subchondral bone. The research uncovers how different loads and frequencies of training, particularly those simulating gallop speeds, significantly affect the energy loss and stiffness in the bone, ultimately leading to its damage.

Research Context and Goal

• This study revolves around understanding fatigue-induced subchondral bone (SCB) injuries, which are common in in athletes due to repetitive high-magnitude loads applied to joints in intensive physical training.
• Previous studies on bone fatigue have used a standard approach, applying loads of a constant magnitude and frequency. However, physiological or realistic loading involves various load magnitudes and frequencies. Such conditions have been studied in metal materials, but limited work has been done on biological materials like bones.
• The goal of the research is to investigate the fatigue behavior of SCB under diverse loads that would occur during a “fast-workout” of an equine athlete or racehorse under training.

Methodology

• The study developed a loading protocol simulating physiological loads during a fast-workout of a racehorse in training. The protocol included warm-up and cool-down stages before and after a training loop, which is made up of slow/fast/slow phases of gallop.
• This loading protocol was applied at room temperature to cylindrical SCB specimens collected from third metacarpal medial condyles (MCIII) of twelve thoroughbred racehorses. This was repeated until the SCBs reached fatigue failure.

Results and Findings

• The findings of the study show that the average total time-to-failure for the specimens was equivalent to about 18.3 training sessions.
• The maximum relative energy loss was found under loads equivalent to gallop speeds, and all specimens failed under these gallop loads. This underlines the importance of gallop speeds in the development of SCB injury, a finding consistent with observations in live racehorses.
• Additionally, specimens with higher average relative energy loss and lower mean stiffness during the first loop exhibited shorter fatigue life, confirming that high energy loss has a detrimental effect on SCB.

Research Implications and Future Work

• The findings of this study highlight the need for further research to understand the correlation of these results with the fatigue injuries seen in equine athletes, and how different training programs can influence the fatigue behavior of the subchondral bone.