Lay Summary Fatigue, as a product of exhaustive exercise, is a complex process that impacts multiple physiological systems in the horse. Refinement of blood biomarker changes over the course of post-exercise recovery are required to direct management decisions regarding the return to work. Adult Thoroughbred horses performed 3 incremental exercise tests to exhaustion on a high-speed treadmill at 48 h intervals with blood and muscle samples collected after each test. Analysis of tissue samples for biomarkers of energy metabolism and muscle damage indicate that multiple bouts of exercise caused neither irreparable muscle damage nor affected glycogen content. By contrast, plasma concentrations of β-hydroxybutyrate, a ketone body, and the branched amino acids, Ile and Val, accumulated with sequential bouts of exercise. Although gallop speeds increased following an 8-wk training program, the altered plasma profiles occurred independent of fitness status. Results from the experiment indicate that training improves athletic performance, as expected, but post-exercise metabolic recovery from fatiguing exercise requires more than 48 h as indicated by changes in plasma amino acid and BHB concentrations.
Lungu et al. (Tue,) studied this question.