Bone fatigue and its implications for injuries in racehorses.
Authors: Martig S, Chen W, Lee P V S, Whitton R C
Journal: Equine veterinary journal
Summary
# Bone Fatigue and Racehorses: Why Training Load Matters Repeated high-speed work in racehorses creates cumulative microcrack damage in bone that accumulates faster than the body can repair it, particularly in the fetlock where joint loads are highest and subchondral bone injuries predominate. Martig and colleagues applied material science principles to equine bone, demonstrating that fatigue life decreases exponentially as loading increases—meaning that modest increases in speed or intensity can dramatically reduce the number of loading cycles a bone can tolerate before failure. A critical finding was that bone remodelling (the repair process) is suppressed during intense race training but accelerated during rest, yet the initial remodelling phase involves bone resorption that temporarily increases porosity and weakens the structure, potentially setting up a porous bone to fail earlier than one that has fully adapted. The practical implication for practitioners is that maximising bone adaptation in young racehorses requires careful periodisation: whilst appropriate training stimulus drives beneficial bone adaptation, unlimited exposure to high-speed work will exceed any bone's capacity to repair itself, making rest periods and duration limits on fast work essential injury prevention strategies. Further research is needed to define optimal training-rest ratios that balance the competing demands of bone adaptation and damage accumulation.
Read the full abstract on PubMed
Practical Takeaways
- •Limit duration of high-speed work and institute appropriate rest periods to manage bone fatigue accumulation, as remodelling inhibition at training extremes may be unavoidable
- •Recognize that porous bone following rest periods may fail earlier than fully adapted bone, so progressive conditioning is essential for young racehorses
- •Understand that even well-adapted bones accumulate microdamage and require ongoing remodelling, making continuous monitoring and strategic training design critical for injury prevention
Key Findings
- •Highest joint loads occur in the fetlock, which is the most common site of subchondral bone injury in racehorses
- •Fatigue life decreases exponentially with increasing load, and loads within the limb increase with speed
- •Fatigue injuries develop when microdamage accumulates faster than bone remodelling can repair it
- •Remodelling of the equine metacarpus is reduced during race training and accelerated during rest periods, with initial resorption weakening bone through increased porosity