People should exercise at a moderate intensity for at least 150 minutes per week, according to recommendations from the American College of Sports Medicine and the U.S. Surgeon General.  Many People have difficulty reaching this modest goal.  A Canadian study from McMaster University found that exercising intensely for 30 minutes per week reduced blood sugar and increased the concentration of mitochondria (the energy centers of the cells).  Previous studies by Canadian scientists showed that training at maximum intensity has dramatic effects on fitness and metabolic capacity.  (Journal Applied Physiology, 111: 1554-1560, 2011)