Altitude-dependent Effects of Concentric and Eccentric Exercise on Glucose Metabolism in Pre-diabetic Men

Concentric (CE) and eccentric (EE) exercises may differently affect glucose metabolism which may be additionally modified when exercises are performed in hypoxia, e.g. at moderate (1500 - 2500 m) or high (2500 - 3500 m) altitudes. However, data on the effects of glucose metabolism due to CE and EE in hypoxia are scarce but would be of utmost importance considering the increasing number of persons suffering from impaired glucose tolerance or diabetes and the unique opportunities provided by the mountainous regions of the Alps to perform CE (e.g. uphill hiking) and EE (downhill hiking, downhill skiing) at altitude between 1500 - 3500 m. Metabolic responses to exercise may be largely mediated by interleukin 6 (IL-6), which is predominantly derived from the contracting limbs and may support the maintenance of metabolic homeostasis during exercise. In addition, IL-6 is elevated with acute and chronic altitude exposure at least partly mediated via adrenergic stimulation. Thus, the type of exercise as well as hypoxia may contribute to IL-6 elevations and differences in serum IL-6 concentrations might help to explain distinctions between responses of glucose metabolism to CE and EE at low and moderate to high altitude.

32 male subjects suffering from pre-diabetes will be randomly assigned to a downhill (EE) or uphill (CE) walking group performing 9 sessions at low altitude (860 - 1360 m) and 9 sessions at moderate to high altitude (2000 - 2500 m). Between normoxic and hypoxic condition will be a break of approximately 12 month. Measurements of glucose metabolism, IL-6 plasma concentration will be performed pre, mid (day 5) and post intervention. Moreover anthropometric, strength and exercise capacity characteristics will be performed pre and post intervention.

We hypothesize that EE in hypoxia is more effective in the modulation of glycemic control in pre-diabetic men than CE in hypoxia as well as EE and CE in normoxia. It is suggested that effects on glucose metabolism are associated with changes in plasma IL-6 concentrations. EE in hypoxia is expected to result in a more persistent rise of plasma IL-6 concentration than CE in hypoxia and in normoxia and to a more pronounced rise in plasma IL-6 than EE in normoxia.