In an ongoing attempt to find easily detectable red flags of overtraining, researchers have learned that certain hormones wave their colors particularly well.

Cortisol, adrenocorticotropic hormone (ACTH), testosterone, leptin, insulin, and other hormones could soon become reliable biomarkers in blood tests to determine if a horse is overworked, according to Concetta Amato, PhD, researcher in the nutrition and endocrinology unit of the French National Veterinary School in Nantes, France.

“Regular, standardized testing of the hormone profile could provide crucial and precocious information about the physiological evolution of the horse’s condition during training, with any changes in that profile being a potential indicator of fatigue and the risk of overtraining,” Amato said during her presentation at the French Equine Research Day held Feb. 28 in Paris.

Amato and her fellow researchers followed 37 Lusitanos and purebred Spanish horses used in public performance shows in France over an 11-month period. They evaluated horses regularly for weight, body condition, and hormone concentrations in the blood via a blood test. Meanwhile, they recorded the horses’ exercise intensity for the period of each evaluation