Insulin sensitivity and muscle characteristics in calves at different levels of physical activity

This study was undertaken to investigate insulin sensitivity and muscle characteristics in calves at different levels of physical activity. Ten male calves of the Swedish Holstein breed were allocated to either an exercise or a non-exercise group. The exercise group performed light work on a treadmill, 5-15 min at 10-12 occasions during 4-5 weeks. The treadmill speed varied from 0.6 to 1.5 m/s. At the beginning and end of the experimental period, the hyperinsulinemic euglycemic clamp technique was used to assess insulin sensitivity and gluteus medius muscle biopsies specimens were obtained for histochemical and biochemical analyses. There were no significant differences in insulin sensitivity, muscle fibre types, enzyme activities or glycogen content between the groups before or after the experimental period. The areas of type I, IIA, IIB fibres and mean muscle fibre area increased significantly in both groups during the experimental period. Muscle fibre characteristics and insulin sensitivity varied among the calves. Insulin sensitivity correlated positively to the percentage of type I fibres at the start of the experiment, and negatively to the mean muscle fibre area at the end of the experimental period. The results indicate that insulin sensitivity in young calves is associated with the change seen in muscle fibre areas with growth, but not by a short period of light physical activity.