Peak Performance or Burnout? Diagnosing Overtraining Syndrome in Equine Athletes by Hormone Analysis

by Fran Jurga | 10 March 2010 | The Jurga Report at

Researchers at the University of Utrecht in The Netherlands created a variety of training and overtraining conditions in a group of Standardbred geldings. They trained them methodically on treadmills, similar to the one in this Erik Buehler photo taken at Kansas State University.

A few weeks ago, I was bemoaning the absence of horses from the landscape of British Columbia during the otherwise-no-complaints 2010 Winter Olympic Games. The more I watched the Olympics, the more I wondered about how the athletes trained during the off (non-snow) season, and how they avoided overtraining.

How do those speed skaters and cross-country skiiers and snowboarders know when to stop training? How fit is too fit? And what about the athletes who do burnout? It reminded me of what we go through with sport horses and racehorses that are now year-round athletes; the calendars used to allow them a season off, but not anymore.

Are there parallels between horse and human athletes? To my surprise (and delight), I came across some recent research that suggests that future Olympic athletes may have some thanks to offer to our equine friends.

There is a science of training, as any racing, endurance or eventing trainer will tell you, that involves deciding when each horse in your care will peak based on a given training program, and adjusting that training program to fit the calendar for a given competition, as well as changes in terrain, footing, altitude, weather and the horse’s mental state because of shipping, breeding or other interruptions.

There’s a science, a culture, an industry and a mythology of training when it comes to human athletes. But science has been a little light when it comes to the problem of predicting and reliably diagnosing overtraining.

Equine sportsmedicine thinks that it has something to offer the bigger sports world, and overtraining research is a great example. The prevalence of both human and equine stress-related illnesses is increasing, so the need is real.

Equine physiology researchers report in a recently published paper that they succeeded in diagnosing equine overtraining syndrome by measuring fluctuations in levels of nocturnal growth hormone secretion.Until now, no diagnostic test was available to determine overtraining syndrome with certainty in any species.

Researchers at the University of Utrecht in the Netherlands put a group of Standardbred horses into parallel training programs; some of the horses were worked to peak fitness and kept working. The study ranged through acclimatisation, training, intensified training and recovery period for the horses; there was a test week at the end of each phase. After the training period the horses were randomly divided into a control group and an intensified trained (IT) group. Standardized exercise tests were used to monitor performance. Behavior was also monitored.The growth hormone axis as well as glucose metabolism were monitored to detect hormonal disturbances.

According to lead researcher Ellen De Graaf-Roelfsema’s summary statement, “The performance of the horses increased during the training period, however during the intensified training period the IT group showed a decrease in performance despite the fact that the horses were more intensively trained than the control horses. The horses changed their gait from trot to gallop or even stopped during the training. Symptoms are indicative of overtraining.”

De Graaf-Roelfsema also noted: “During the intensified training period the IT horses showed obvious changes in mood state. The horses were less interested in the environment and in other unknown horses as was shown in different behavioral changes.”According to the research paper, overtraining syndrome is clinically recognized by reduced performance despite the same or an increased level of training. The researchers found that secretion of the growth hormone was an indicator for overtraining syndrome. This hormone plays a role in both growth and stress. The researchers were able to diagnose overtraining syndrome by measuring the amount of hormone present in the horse’s blood. They found distinct variations between the groups of horses depending on the types and intensity of training programs.

The way that horses and humans express growth hormone under exercise stress could be remarkably parallel and predictable. The Dutch veterinary researchers feel confident that the horse can easily serve as a model for human athletes for studying overtraining or possibly other stress-related pathophysiological mechanisms.

Among the more than 200 symptoms described for overtraining syndrome among human athletes, not one has yet been determined to be specific to the disease’s clinical picture. For humans, a Profile of Mood State (POMS) assessment tool is used to diagnose overtraining syndrome. This tool measures changes in behavior and mental state, which so far appear to be the most reliable indicators of overtraining syndrome.

Further study should reveal whether measuring nocturnal growth hormone secretion, as is done with horses, can also be applied to humans.

The lead author of this study, Ellen de Graaf-Roelfsema, received her PhD from the University of Utrecht by studying overtraining in horses, particularly the role of growth hormone and glucose.To learn more: E. de Graaf-Roelfsema, P.P. Veldhuis, H.A. Keizer, M.M. van Ginneken, K.G. van Dam, M.L. Johnson, A. Barneveld, P.P. Menheere, E. van Breda, I.D. Wijnberg, J.H. van der Kolk: “Overtrained horses alter their resting pulsatile growth hormone secretion” in American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. (Click on link to download a PDF file of the complete paper.)

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