While visibly obvious, fatigue is hard to quantify. Electromyography (EMG) measures conduction along nerves in a particular muscle group--as muscle fibers fatigue, EMG signals shift from high to low. Taking EMG readings during galloping is unreliable, however, because signals are susceptible to inaccuracies from lead changes. Kinematics is another evaluation technique designed for use on moving animals. It uses reflective markers on the horse to follow stride length, duration, and vertical climb.

Researchers from the University of Bristol in the United Kingdom recently set out to combine the strengths of EMG and kinematic analysis to chart the changes in one muscle, the deltoid, as horses raced to fatigue. Their hypothesis was that EMG signal would decrease in tandem with changes in stride character throughout the test.

Three racehorses were galloped at 110% of maximum aerobic capacity (based on oxygen usage) on an inclined treadmill until they could no longer keep pace with the treadmill. EMG readings and kinematic data indicated that as the horses got tired, each stride took longer and the horses rose off the ground higher. As hoped, EMG signal decreased by as much as 36% along with these stride indicators of increasing fatigue, lending support to the use of EMG along with kinematic analysis for studying fatigue in horses.

The authors point out that this was only a pilot project, but the promising results suggest further study of this method.

Colbourne, GR; Birtles, DM; Cacchione, IC. Equine Veterinary Journal Supplement, 33, 89-93, 2001.

About the Author

Susan Piscopo, DVM, PhD

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

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