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Early Tendon Damage in Racehorses? 10% CSA Increase May Be the Warning Sign
American Journal of Veterinary Research 2025
Obi Veterinary Education
August 23, 2025
Audrey Beaumont, Anne-Laure Emond, Philippe Pourcelot, Lauriane Fayaubot, Bérangère Ravary-Plumioen, Anne-Gaelle Dupays, Loïc Desquilbet, Jean-Marie Denoix, Nathalie Crevier-Denoix
Background
Tendinopathy of the superficial digital flexor tendon (SDFT) is a significant cause of performance loss in racehorses, particularly under high-speed exercise. Adaptation of tendons to training may involve increased cross-sectional area (CSA), which reduces stress. While this has been studied in Thoroughbreds, no prospective, longitudinal research had examined SDFT adaptation in Trotter horses. This study aimed to quantify CSA changes in young French Trotters during early training and explore whether CSA changes could indicate early tendon damage.
Methods
Twelve healthy, 3-year-old French Trotters were trained for four months on either a soft sand track (n=6) or a hard sand track (n=6) under an identical progressive exercise program. Ultrasonography of both forelimb SDFTs was performed before training (D0), after 2 months (M2), and after 4 months (M4). CSA was measured at the midmetacarpus, and percentage changes over time were calculated. Horses developing tendinopathy by M4 were analyzed separately. Statistical comparisons used mixed-effects regression and Mann-Whitney tests.
Results
Three of six horses on the hard track developed bilateral SDFT tendinopathy by M4. In uninjured tendons (n=18), CSA increased significantly (+6.8%) from D0 to M2, then decreased slightly (−2.3%) from M2 to M4 despite increased training intensity. Injured tendons showed a significantly greater CSA increase from D0 to M2 (+13%) and a further large increase from M2 to M4 (+27.9%). ROC analysis indicated that a CSA increase ≥9.84% in the first 2 months identified all tendons that later became injured (100% sensitivity, 77.8% specificity).
Limitations
The study involved a small sample size and only one breed and age group. Horses were trained in one direction (anticlockwise), and CSA was measured at a single site, which may not capture all injury-prone regions. No non-training control group was included, and tendon material properties were not assessed.
Conclusions
In young Trotters, SDFT CSA increases significantly during the first two months of training, suggesting adaptive changes. A CSA increase of around 10% in this period may indicate early tendon damage risk. These findings support ultrasonographic CSA monitoring as a potential tool for early detection and prevention of SDFT injuries.
Ultrasonographic images of the left forelimb SDFT of a 3-year-old French Trotter after 4 months of training on a hard sand track. Image A, recorded at the midmetacarpus, is 1 of the 5 images in the transverse section used for the SDFT CSA measurement (methods illustrated in Figure 1). Images B through G, acquired with a lower magnification compared to image A, come from the ultrasonographic proximodistal screening performed to document the injury (independently from the CSA measurement). Images B and C are just proximal and distal (respectively) to the midmetacarpus level (where image A was recorded). Images B through G show that the maximal severity zone of the lesion is slightly distal (here, of 2 to 3 cm) to the CSA measurement site.
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