The cross-sectional area of normal superficial digital flexor tendon of young French Trotters increases during the first months of training.

The study investigated changes in the cross-sectional area (CSA) of the midmetacarpal superficial digital flexor tendons (SDFTs) in young French Trotters during a four-month training program. It found that the tendon CSA increased during the initial months of training while the horse was uninjured and that those tendons with early damage had a larger percent increase in CSA.

Methodology

• In this experimental study, twelve 3-year-old French Trotters were divided into two groups to train on either a soft or hard tack.
• The two groups followed the same exercise program, which gradually increased in intensity over a four-month period.
• At three different points—before the training (D0), two months into the training (M2), and at the end of the four-month training (M4)—ultrasonographic exams were performed on the SDFT of each forelimb of the horses.
• Measurement of the SDFT’s CSA at the midmetacarpus was taken at each examination, and the percentage change of CSA over time was calculated.

Findings

• Out of the horses trained on the hard track, half developed bilateral SDFT tendinopathy by the end of the training.
• The SDFT CSA of the horses that did not develop tendinopathy increased by an average of 6.8% after two months and 4.3% after four months.
• Oddly enough, the CSA change dropped by 2.3% between the second and fourth month of training despite an increase in exercise intensity.
• For those tendons that eventually developed tendinopathy at M4 (even though they were asymptomatic at M2), the CSA’s percent increase from D0 to M2 was significantly larger (+13%). This increase continued from M2 to M4, resulting in a net gain of 27.9%.

Conclusion

• The research suggests that during initial training phases, trotting horses experience adaptive changes to exercise which affect the SDFT CSA. Furthermore, those early tendon damages manifest as larger increases in CSA.
• Based on the findings, the researchers recommend veterinarians and horse trainers to suspect early tendon damage if they observe an increase in CSA by 10% or more within two months of starting a training program.