Muscle adaptation of Thoroughbred racehorses trained on a flat or sloped track

Hirofumi Miyata From the Department of Biological Sciences, Faculty of Agriculture (Miyata), Department of Exercise and Health Science, Faculty of Education (Sugiura), and Department of Veterinary Physiology, Faculty of Agriculture (Tokuriki), Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8515, Japan; and the Equine Research Institute, Japan Racing Association, Tokami 321-4, Utsunomiya, Tochigi 320-0856, Japan (Kai, Hiraga).

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Takao Sugiura From the Department of Biological Sciences, Faculty of Agriculture (Miyata), Department of Exercise and Health Science, Faculty of Education (Sugiura), and Department of Veterinary Physiology, Faculty of Agriculture (Tokuriki), Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8515, Japan; and the Equine Research Institute, Japan Racing Association, Tokami 321-4, Utsunomiya, Tochigi 320-0856, Japan (Kai, Hiraga).

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Makoto Kai From the Department of Biological Sciences, Faculty of Agriculture (Miyata), Department of Exercise and Health Science, Faculty of Education (Sugiura), and Department of Veterinary Physiology, Faculty of Agriculture (Tokuriki), Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8515, Japan; and the Equine Research Institute, Japan Racing Association, Tokami 321-4, Utsunomiya, Tochigi 320-0856, Japan (Kai, Hiraga).

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Atsushi Hiraga From the Department of Biological Sciences, Faculty of Agriculture (Miyata), Department of Exercise and Health Science, Faculty of Education (Sugiura), and Department of Veterinary Physiology, Faculty of Agriculture (Tokuriki), Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8515, Japan; and the Equine Research Institute, Japan Racing Association, Tokami 321-4, Utsunomiya, Tochigi 320-0856, Japan (Kai, Hiraga).

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Mikihiko Tokuriki From the Department of Biological Sciences, Faculty of Agriculture (Miyata), Department of Exercise and Health Science, Faculty of Education (Sugiura), and Department of Veterinary Physiology, Faculty of Agriculture (Tokuriki), Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8515, Japan; and the Equine Research Institute, Japan Racing Association, Tokami 321-4, Utsunomiya, Tochigi 320-0856, Japan (Kai, Hiraga).

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Abstract

Objective

To determine histochemical and biochemical properties of muscle during adaptation to training on a flat or sloped track.

Animals

22 Thoroughbreds.

Procedure

Samples were obtained from the middle gluteus muscle before and after training programs were conducted, using a needle-biopsy technique. Training programs consisted of horses running 1,600 m on a flat or sloped track for 16 weeks. Amplitude of middle gluteus muscle activity per burst was calculated. Muscle fiber composition and area were examined on serial cross sections processed by standard histochemical staining procedures (ATPase stain after prior incubation with an acid or base, followed by succinate dehydrogenase [SDH] stain). Furthermore, SDH and phosphofructokinase activities were determined biochemically, and composition of myosin heavy chain (MHC) isoforms was analyzed electrophoretically.

Results

Training resulted in substantial adaptations. Relative contribution of muscle fiber with high SDH activity (type-I and -IIa fibers) to total cross-sectional area, SDH activity, and composition of MHC-IIa isoforms were increased. Gel electrophoresis revealed a large amount of MHC-IIx isoform and a small amount of MHC-IIb isoform in the muscle. Although root mean square of muscle activity for training on a sloped track was 7.6% higher than the value obtained while training on a flat track, muscle histochemical and biochemical properties did not differ significantly between groups training on flat and sloped tracks.

Conclusions

Training adaptations for contractile and metabolic properties of the middle gluteus muscle were evident for the 2 types of training. However, training adaptations did not differ significantly between groups trained on flat or sloped tracks. (Am J Vet Res 1999;60:1536–1539)

Abstract

Objective

To determine histochemical and biochemical properties of muscle during adaptation to training on a flat or sloped track.

Animals

22 Thoroughbreds.

Procedure

Samples were obtained from the middle gluteus muscle before and after training programs were conducted, using a needle-biopsy technique. Training programs consisted of horses running 1,600 m on a flat or sloped track for 16 weeks. Amplitude of middle gluteus muscle activity per burst was calculated. Muscle fiber composition and area were examined on serial cross sections processed by standard histochemical staining procedures (ATPase stain after prior incubation with an acid or base, followed by succinate dehydrogenase [SDH] stain). Furthermore, SDH and phosphofructokinase activities were determined biochemically, and composition of myosin heavy chain (MHC) isoforms was analyzed electrophoretically.

Results

Training resulted in substantial adaptations. Relative contribution of muscle fiber with high SDH activity (type-I and -IIa fibers) to total cross-sectional area, SDH activity, and composition of MHC-IIa isoforms were increased. Gel electrophoresis revealed a large amount of MHC-IIx isoform and a small amount of MHC-IIb isoform in the muscle. Although root mean square of muscle activity for training on a sloped track was 7.6% higher than the value obtained while training on a flat track, muscle histochemical and biochemical properties did not differ significantly between groups training on flat and sloped tracks.

Conclusions

Training adaptations for contractile and metabolic properties of the middle gluteus muscle were evident for the 2 types of training. However, training adaptations did not differ significantly between groups trained on flat or sloped tracks. (Am J Vet Res 1999;60:1536–1539)

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