The Thoroughbred racehorse is capable of maintaining speeds of approximately 17 m/s for distances of over a mile. This represents an average speed and the Thoroughbred can reach speeds in excess of 20 m/s over short distances. The present series of studies was undertaken to
investigate further the metabolic response to high-intensity exercise in
the Thoroughbred racehorse.
Unlike man, high-intensity exercise in the horse results in an increase in packed cell volume. This in turn causes acute changes in the colligative properties of blood and plasma. The changes in these properties
were investigated and the effect on calculation and distribution of
metabolites in blood and muscle was determined. The horse has a high capacity for lactate production compared to man
and existing methodology for the assessment of muscle buffering capacity in
biopsy samples was further developed and investigated. The horse was found
to have a significantly higher muscle buffering capacity compared with man
and it was calculated that this could be explained wholly on the basis of
the higher muscle carnosine content in the horse. The metabolic response to high-intensity exercise was investigated
using several exercise models, including single and multiple field gallops
and treadmill exercise. A consistent finding was that high-intensity exercise in the Thoroughbred racehorse was nearly always accompanied by a reduction in muscle ATP content. The nature of the ATP decrease was further investigated using a treadmill exercise model. Muscle ATP decrease was
found to occur at a particular exercise intensity rather than show a
gradual decrease with increasing intensity. The intensity at which muscle
ATP content began to decline significantly varied between individual
horses, but in each case appeared to coincide with muscle lactate contents
of approximately 70 mmol/kg dry muscle. The significance of the decline in
ATP is discussed
