Effect of growth and training on muscle adaptation in Thoroughbred horses.
OBJECTIVE
To determine the effect of growth and training on metabolic properties in muscle fibers of the gluteus medius muscle in adolescent Thoroughbred horses.


METHODS
Twenty 2-year-old Thoroughbreds.


METHODS
Horses were randomly assigned to 2 groups. Horses in the training group were trained for 16 weeks, and control horses were kept on pasture without training. Samples were obtained by use of a needle-biopsy technique from the middle gluteus muscle of each horse before and after the training period. Composition and oxidative enzyme (succinic dehydrogenase [SDHI) activity of each fiber type were determined by use of quantitative histochemical staining procedures. Whole-muscle activity of SDH and glycolytic enzyme (phosphofructokinase) as well as myosin heavy-chain isoforms were analyzed biochemically and electrophoretically, respectively.


RESULTS
The SDH activity of type-I and -IIA fibers increased during growth, whereas whole-muscle activity was unchanged. Percentage of type-IIX/B muscle fibers decreased during training, whereas that of myosin heavy-chain IIa increased. The SDH activity of each fiber type as well as whole-muscle SDH activity increased during training. An especially noticeable increase in SDH activity was found in type-IIX/B fibers.


CONCLUSIONS
Changes in muscle fibers of adolescent Thoroughbreds are caused by training and not by growth. The most noticeable change was for the SDH activity of type-IIX/B fibers. These changes in the gluteus medius muscle of adolescent Thoroughbreds were considered to be appropriate adaptations to running middle distances at high speeds.
Yamano
Seiko
S
Department of Biological Sciences, Faculty of Agriculture, Yamaguchi University, Japan.
Eto
Daisuke
D
Sugiura
Takao
T
Kai
Makoto
M
Hiraga
Atsushi
A
Tokuriki
Mikihiko
M
Miyata
Hirofumi
H
D000222:Adaptation, Physiological; D000818:Animals; D006736:Horses / Q000502:physiology*; D007527:Isoenzymes / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000502:physiology; D018482:Muscle, Skeletal / Q000201:enzymology / Q000254:growth & development* / Q000502:physiology*; D025221:Phosphofructokinases / Q000378:metabolism; D010805:Physical Conditioning, Animal / Q000502:physiology*; D013385:Succinate Dehydrogenase / Q000378:metabolism
D007527:Isoenzymes; D013385:Succinate Dehydrogenase; D025221:Phosphofructokinases