This thesis investigated (1) effects of short term training (STT) and detraining on insulin sensitivity (SI), expression of GLUT-4 and activities of glycogen synthase (GS) and hexokinase (HK) in equine skeletal muscle and (2) effect of dietary non-structural carbohydrate (NSC) content and physical conditioning on these measurements. STT resulted in increased whole body SI, GLUT-4 protein content and GS activity in skeletal muscle. Enhancements in SI, GLUT-4 protein and GS activity were still evident after detraining. Adaptation to a high NSC diet was associated with development of a compensated insulin resistance that was partially mitigated by physical conditioning. Increased GLUT-4 protein expression and GS and HK activity may have contributed to this improvement in SI. Results demonstrated physical conditioning may attenuate changes in SI resulting from a high NSC diet by improved glucose transport and increased GS and HK activity, and that STT improvements in SI, GLUT-4 protein content and GS activity are still evident following 5 days inactivity.