The effects of overtraining on blood volumes in standardbred racehorses.
Authors: Golland L C, Evans D L, McGowan C M, Hodgson D R, Rose R J
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Overtraining and Blood Volume in Standardbred Horses Overtraining syndrome in racehorses has long been associated with reduced exercise capacity, and practitioners have previously used elevated red blood cell volume as a potential diagnostic marker. Golland and colleagues investigated this relationship prospectively across 12 Standardbreds, measuring plasma, blood and red cell volumes at weeks 8 and 32 of a controlled training programme; six horses underwent intensified overload training whilst six continued standard conditioning. Contrary to expectations, overload training produced no significant changes in absolute blood or red cell volumes—these parameters actually decreased significantly over time in both groups—though maximal post-exercise haematocrit was notably lower in the overrained group by week 32 (0.57 versus 0.59 L/L). This finding challenges the long-held assumption that red cell hypervolaemia drives the performance decline seen in overtraining, suggesting instead that loss of racing capacity stems from alternative physiological mechanisms. For equine professionals managing training loads, this indicates that blood volume measurements alone cannot reliably diagnose overtraining, and that identifying overtraining syndrome requires assessment of additional parameters such as heart rate recovery, lactate kinetics, behaviour and hormonal markers rather than relying on haematocrit values.
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Practical Takeaways
- •Overtraining in racehorses cannot be diagnosed by detecting red blood cell hypervolaemia, as this does not occur with overload training protocols
- •Practitioners should not rely on blood volume measurements as a diagnostic tool for identifying overtraining syndrome in Standardbred racehorses
- •The mechanism of decreased exercise performance in overtrained horses involves factors other than blood volume changes, suggesting need for alternative diagnostic approaches
Key Findings
- •No significant effects of overload training on plasma, blood, or total red cell volumes between weeks 8 and 32 of the study
- •Blood volumes significantly decreased with time in both OLT and control groups
- •Maximal haematocrit after exercise was significantly lower in the overtraining group at week 32 (0.57±0.003 L/L) compared to week 8 (0.59±0.004 L/L)
- •Red cell hypervolaemia is not a mechanism for the decrease in exercise capacity associated with overtraining in Standardbred horses