Reasons for performing study: Although the main cause of injury to the superficial digital flexor tendon (SDFT) is assumed to be high intensity loading of the tendon, to date the forces exerted on the SDFT during cantering have never been measured.
Objective: To measure the force exerted on the SDFT at walk, trot and canter on a treadmill.
Methods: Arthroscopically implantable force probes (AIFP) were implanted in the SDFT of the left and right forelimbs of 8 Thoroughbred horses (480–565 kg). The output of the AIFP was calibrated using the SDFT force calculated by inverse dynamics and an in vitro model of the lower forelimb at trot. The AIFP output was recorded at 1000 Hz at the walk, trot and canter (9 m/s) on a flat treadmill.
Results: AIFP data were analysed successfully in 13 measurement sessions at the walk and trot, in the leading forelimb in 8 sessions at canter and in the trailing forelimb in 5 sessions at canter. The mean ± s.d. maximal force in the SDFT was 3110 ± 1787 N at the walk, 5652 ± 2472 N at the trot, 7030 ± 2948 N in the leading forelimb and 6453 ± 2940 N in the trailing forelimb at canter.
Conclusions: The force in the SDFT increases with running speed from the walk to the canter. The force in the SDFT could not be measured at the gallop. Further study is needed to determine the force in the SDFT at high speed, because it is important for preventing injuries to the SDFT to limit overloading of this tendon.