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Effects of intensified training and subsequent reduced training on glucose metabolism rate and peripheral insulin sensitivity in Standardbreds

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  • 1 Department of Equine Sciences, Medicine Section, Faculty of Veterinary Medicine, Utrecht University, Utrecht, 3584 CM Utrecht, The Netherlands.
  • | 2 Department of Human Physiology and Sports Medicine, Free University of Brussels, 1050 Brussels, Belgium.
  • | 3 Department of Movement Sciences, Faculty of Health Sciences, University of Maastricht, 6211 Maastricht, The Netherlands.
  • | 4 Department of Equine Sciences, Medicine Section, Faculty of Veterinary Medicine, Utrecht University, Utrecht, 3584 CM Utrecht, The Netherlands.
  • | 5 Department of Equine Sciences, Medicine Section, Faculty of Veterinary Medicine, Utrecht University, Utrecht, 3584 CM Utrecht, The Netherlands.

Abstract

Objective—To determine the influence of intensified training and subsequent reduced training on glucose metabolism rate and peripheral insulin sensitivity in horses and identify potential markers indicative of early overtraining.

Animals—12 Standardbred geldings.

Procedures—Horses underwent 4 phases of treadmill-based training. In phase 1, horses were habituated to the treadmill. In phase 2, endurance training was alternated with high-intensity exercise training. In phase 3, horses were divided into control and intensified training groups. In the intensified training group, training intensity, duration, and frequency were further increased via a protocol to induce overtraining; in the control group, these factors remained unaltered. In phase 4, training intensity was reduced. Standardized exercise tests were performed after each phase and hyperinsulinemic euglycemic clamp (HEC) tests were performed after phases 2, 3, and 4.

Results—10 of 12 horses completed the study. Dissociation between mean glucose metabolism rate and mean glucose metabolism rate-to-plasma insulin concentration ratio (M:I) was evident in the intensified training group during steady state of HEC testing after phases 3 and 4. After phase 4, mean glucose metabolism rate was significantly decreased (from 31.1 ± 6.8 μmol/kg/min to 18.1 ± 3.4 μmol/kg/min), as was M:I (from 1.05 ± 0.31 to 0.62 ± 0.17) during steady state in the intensified training group, compared with phase 3 values for the same horses.

Conclusions and Clinical Relevance—Dissociation between the glucose metabolism rate and M:I in horses that underwent intensified training may reflect non-insulin–dependent increases in glucose metabolism.

Contributor Notes

Presented in abstract form at the Conference on Equine Sports Medicine and Science, Utrecht, The Netherlands, July 2008.

The authors thank Karel Tims, Emma Blok, Cornélie Westermann, Peggy Laan, Petty Vos, Kim Hardeveld, Marjorie Pollak, Sophie Wolfert, Ilvy van den Broek, Annemiek Maaskant, Marleen Jager, Sabine Brummel, and Esmee Smiet for assistance with the hyperinsulinemic euglycemic clamp; Andries Klaarenbeek and Henk van Voorst for training of the horses; and Lyde Bijlsma-Heyting for determination of insulin concentrations.

Address correspondence to Dr. de Graaf-Roelfsema (e.roelfsema@uu.nl).