Exercise interval training: an improved stimulus for improving the physiology of pre-diabetes

Current reports estimate that type II diabetes (T2D) affects 5-8% of adults. Also recognized is a transitional group of patients whose fasting blood glucose is abnormal; yet, not considered high enough to be diagnosed as diabetes. Defined as "pre-diabetes" these individuals have impaired fasting glucose (IFG; fasting glucose 100-125 mg/dL), impaired glucose tolerance (IGT; 2 h glucose 140-199 mg/dL) or both. Two unifying features associated with IFG and IGT are their strong links to obesity and physical inactivity, which lead independently and collectively toward the erosion of various cellular processes affecting glucose control. In contrast, regular exercise positively influences IFG/IGT and obesity, thus representing an important therapy for preventing diabetes via the enhancement of several mechanisms of action. These include improved glucose metabolism, muscle respiratory capacity, mitochondrial respiratory chain activity and beta-oxidation. Contemporary exercise guidelines provided by various organizations recommend that exercise be performed at intensities ranging from 40% to 85% of maximal aerobic capacity. Unfortunately, little is known regarding the optimal intensity to best facilitate the physiological benefits associated with exercise. An evolving body of research shows that interval training produces greater changes in exercise capacity than traditional aerobic training. Interval training involves bouts of high exercise intensity (15s to 4 min; >90% VO(2max)) followed by a recovery period (40-50% VO(2max)) of equal or longer duration than the associated work interval. Though the net effect of interval training is aerobic, periodic excursions involving anaerobic energy pathways theoretically "push" the mitochondria to greater improvements in exercise capacity, mitochondrial biogenesis, enzymatic markers associated with glycolysis, aerobic metabolism and beta (beta)-oxidation. Though traditionally viewed as a training modality for athletes, a recent report has demonstrated that interval training is more effective than traditional aerobic exercise training in patients up to approximately 75 y of age and with low functional capacities (VO(2max) 13 ml/kg/min) by producing superior improvements in VO(2max), sub-maximal exercise tolerance, levels of peroxisome proliferator activator protein-gamma co-activator1alpha (PGC-1alpha), and quality of life indices more so than traditional aerobic exercise training. Erosion in these same markers is present in populations with pre-diabetes and T2D. The principal hypothesis of this paper is that interval training will provide a more powerful stimulus for improving insulin sensitivity than traditional low-to-moderate intensity aerobic conditioning. This theory further proposes that these affects will be due to greater changes in specific metabolic pathways associated with glycolysis, aerobic metabolism, beta-oxidation, and mitochondrial biogenesis.