MARE Center, Virginia Tech, 5527 Sullivan's Mill Road, Middlebury, Virginia 20117, USA.
Effects of short-term training on insulin sensitivity and skeletal muscle glucose metabolism in Standardbred horses
Version of Record online: 10 JUN 2010
© 2006 EVJ Ltd
Equine Veterinary Journal
Special Issue: Proceedings of the 7th International Conference of Equine Exercise Physiology
Volume 38, Issue S36, pages 226–232, August 2006
How to Cite
STEWART-HUNT, L., GEOR, R. J. and McCUTCHEON, L. J. (2006), Effects of short-term training on insulin sensitivity and skeletal muscle glucose metabolism in Standardbred horses. Equine Veterinary Journal, 38: 226–232. doi: 10.1111/j.2042-3306.2006.tb05544.x
- Issue online: 10 JUN 2010
- Version of Record online: 10 JUN 2010
- exercise training;
- insulin-mediated glucose disposal;
- skeletal muscle GLUT-4;
- glycogen synthase
Reasons for performing study: Increased insulin sensitivity occurs after a period of exercise training, but the mechanisms underlying this training-associated increase in insulin action have not been investigated.
Objective: To examine the effects of short-term endurance training (7 consecutive days) and a subsequent period of inactivity (5 days) on whole body insulin sensitivity and GLUT-4 protein and the activities of glycogen synthase (GS) and hexokinase (HK) in skeletal muscle. It was hypothesised that training would increase insulin sensitivity in association with increased GLUT-4 protein and activities of GS and HK, but that these changes would be transient, returning to baseline after 5 days of inactivity.
Methods: Seven mature Standardbred horses completed training consisting of 7 consecutive days of 45 min of treadmill exercise at a speed that elicited 55% of pretraining maximal aerobic capacity (VO2peak). Insulin sensitivity was determined by rate of glucose disposal (M) during the last 60 min of a 120 min euglycaemic-hyperinsulinaemic clamp (EHC) performed before (-2 days) and at 1 and 6 days following training. VO2peak was measured before (UT) and after (TR) training and the period of inactivity (IA).
Results: Training resulted in a 9% increase in mean VO2peak (P<0.05) that was maintained following inactivity (IA). Mean M values were more than 2-fold higher (P<0.05) in TR than in UT. Mean M was also higher (P<0.05) in IA when compared to UT. GLUT-4 protien abundancewas more than 10-fold higher in TR and IA (P<0.001) than in UT. Pre-EHC GS activity and GS fractional velocity were increased (P<0.05) in TR when compared to UT and IA. Pre-EHC HK activity was increased (P<0.05) in IA when compared to UT and TR. Muscle glycogen was 66% lower (P<0.05) in TR than in UT and IA.
Conclusions: Short-term training resulted in increases in whole body insulin sensitivity, and GLUT-4 protein content and glycogen synthase activity in skeletal muscle. The enhancements in insulin sensitivity, GLUT-4 protein and glycogen synthase activity were still evident after 5 days of inactivity.
Potential relevance: Insulin resistance in equids has been associated with obesity and predisposition to laminitis. Regular physical activity may mitigate risk of these conditions via enhancement of insulin sensitivity and/or control of bodyweight.