Changes in physiological parameters in overtrained Standardbred racehorses.

The research article is an examination of the effects of high-intensity training overload for a prolonged period on the physiological parameters of Standardbred racehorses, highlighting the potential markers for detecting overtraining in these equine athletes.

Study Design and Methodology

• The researchers conducted a longitudinal study spanning 34 weeks to explore how intense and extended training sessions impact various physiological parameters in Standardbred racehorses.
• The study involved ten Standardbred racehorses that underwent 24 weeks of training, followed by 8 weeks of escalated workload and then a 2-week recovery period.
• To assess the effects of the training protocols on the horses, they were required to perform a 2400 m time trial and a progressive submaximal exercise test on alternating weeks.

Key Findings

• By the end of their intense training program, the horses showed a significant deterioration in their performance: the time they required to finish the final 1200 m of the time trial had increased by an average of 4.0%, and their peak velocity had dropped by 6.9%.
• These observations indicated that the horses had undergone overtraining – the escalated workload had led to a decline in their performance rather than an improvement.
• The study also found that overtraining led to an increase in the horses’ blood lactate concentration after the time trial and the submaximal test. Concurrently, they exhibited decreases in body weight, plasma cortisol concentration, and packed cell volume after the time trial, and in the velocity at a heart rate of 200/minute (V200).

Parameters Not Affected by Overtraining

• Some physiological parameters, however, failed to demonstrate a clear-cut change in response to overtraining. These included the horses’ maximal and recovery heart rates, basal plasma cortisol, plasma and red cell volume, and measures of skeletal muscle damage, namely, the plasma concentrations of creatine kinase and aspartate aminotransferase.

Implications of the Findings

• The research concludes that bodyweight, V200, postexercise blood lactate, and plasma cortisol concentrations could all be potentially useful markers for identifying acute overtraining in equine athletes. This knowledge can help improve the training protocols for horse athletes and prevent the detrimental effects of overtraining on their performance and health.