Superficial digital flexor tendon lesions in racehorses as a sequela to muscle fatigue: a preliminary study.

The research is an exploratory study examining the link between muscle fatigue and injuries in the superficial digital flexor tendon in racehorses, proposing that fatigue in the deep digital flexor muscle leads to excessive loading of the superficial tendon.

Research Objective and Methodology

• The study sought to gain a deeper understanding of the causes or predisposing factors to forelimb superficial digital flexor tendon injuries in racehorses, which are commonly associated with training and racing, and often end a horse’s racing career.
• The research took into consideration the comprehensive system of the distal limb where the injury occurs, which includes the associated muscles.
• The researchers studied muscle and tendon function in vivo, i.e., in living horses, by implanting strain gauges in three Thoroughbred horses. The horses were made to walk, trot, and canter on a motorized treadmill, and the data collected were correlated with assessments of the muscle architecture and fibre composition.

Findings

• The study determined that the superficial digital flexor muscle has fatigue-resistant properties and produces high force. This allows its tendon to store and return elastic energy, predominantly at the trot.
• As the horse’s speed increases, the force on the deep digital flexor tendon also increases, thus stabilizing hyperextension of the fetlock. This action reinforces the superficial digital flexor’s role in limb load support.
• The deep digital flexor muscle, however, has properties that make it susceptible to fatigue due to its ability to contract quickly.
• Based on these findings and related studies, the researchers propose that the deep digital flexor muscle’s susceptibility to fatigue is responsible for overloading the superficial digital flexor tendon.

Conclusions and Recommendations

• The researchers conclude that overuse and fatigue of the deep digital flexor muscle may result in overloading of the superficial digital flexor tendon, leading to injuries often seen in racehorses.
• They recommend that future research should consider the entire distal limb system function to improve diagnostic procedures and exercise training approaches, which may ultimately contribute to more effective prevention and treatment of digital flexor tendon injuries in equine athletes.