Adaptation and overtraining in horses subjected to increasing training loads.

The study explores how increasing training loads affect racehorses, with an emphasis on identifying indicators of overtraining. The authors concluded that overtraining is unlikely as long as intense exercise phases are alternated with lighter ones and no single measure can definitively detect early overtraining.

Study Design and Methodology

• The study involved seven male racehorses subjected to a lengthy period (272 days) of training. This was divided into two kinds of daily exercise: endurance running (which aimed at a heart rate of 140 per minute) and interval training (which targeted maximum heart rate). These were gradually increased in terms of both duration and intensity.
• Every four weeks, the horses were subject to an incremental exercise test. However, this frequency was doubled from day 187 onwards, with tests conducted every two weeks.
• The researchers measured a variety of physiological parameters, including muscle glycogen, muscle lactate, energy-rich phosphates, adrenal response to adrenocorticotropic hormone, plasma and red blood cell volumes, and multiple blood chemistry variables.

Findings

• Some horses started showing signs of weight loss, irritability, and an inability to complete the training once the intensity of the endurance exercise increased. Despite this, there was no decrease in test performance.
• The adrenal response to adrenocorticotropic hormone remained unchanged throughout the period of overtraining.
• During maximal exercise, the decline in muscle ATP concentration was less during the period of perceived staleness, indicating a change in how the horses’ bodies were utilizing energy during intense exercise.
• Other measurements, such as plasma volume, red blood cell volume, and blood chemical variables, remained the same.

Conclusions

• The researchers concluded that overtraining was unlikely to occur as long as the intense training was interspersed with lighter exercises. This points to the importance of a balanced training plan for racehorses to prevent overtraining and ensure optimal performance.
• However, they also concluded that there is no single definitive marker for early detection of overtraining, suggesting that a multi-faceted approach is needed to monitor horses for overtraining during intense exercise regimes.