The Effect of Blood Volume Changes After Bed Rest and Aerobic Exercise Training on the Glucose Tolerance

While there is little doubt that physical inactivity leads to reduced insulin sensitivity and in contrast hereto that physical activity improves insulin sensitivity the underlying mechanisms are still to a large extend unknown. With this study the investigators wish to test two independent hypotheses that may explain the observed changes:

The first hypothesis is that part of the explanation for the known increase in circulating levels of glucose in response to an oral glucose tolerance test (indicating reduced insulin sensitivity) following bed rest is due to a concomitantly reduced blood volume and thereby dilution space.

In addition the investigators also speculate that the reduced glucose response to an oral glucose tolerance test (indicating improved insulin sensitivity) after a training period is related to the exercise induced increase in blood volume, and hence an increased dilution space.

Based on this, the hypothesis to be tested with these two experimental approaches (bed rest and aerobic exercise training), is that at least part of the changes observed in the glucose tolerance following bed rest and aerobic exercise training are related to concomitantly occurring changes in blood volume.

The second hypothesis to be tested is that another important contributor to the changes in circulating glucose levels following an oral glucose tolerance test after bed rest and physical training are related to diminished or improved capacity for skeletal muscle glucose uptake and glycogen storage, respectively. The rationale here fore are that exercise training increases skeletal muscle glycogen content and storage capacity in healthy and type 2 diabetic patients, respectively, and that bed rest does the opposite.