ABC News has just released a news article on this, titled "Why 6 Seconds of Exercise Can Be as Worthwhile as 90 Minutes". Pretty deceptive title though...here's the summary: 6 Seconds: Scottish study showed that senior citizens doing six 6-second sprints on a stationary bike with one minute rest in between lowered their blood pressure after 6 weeks by 9 percent. *But the article didn't say how many repetitions were made. Maybe similar idea for younger people too. Michele Olson (exercise science professor and researcher at Auburn University in Alabama): “Even a little activity can increase the efficiency of your heart and lead to more energy overall, no matter what your age,” she said. 5 Minutes: Journal of the American College of Cardiology published study: 5-minute daily run can cut the risk of death in middle-aged men and women by 30 percent and the risk of dying from cardiovascular disease by 45 percent compared to couch potatoes. Clarification from Olson: “You have to push at a very high intensity to see improvements in heart function and reduce the dangerous, unhealthy visceral fat that collects around the organs” 10 Minutes: Bone health benefits begin to kick in around the 10-minute mark. Olson: “That’s about how much time you need to stress the bones and stimulate bone density to avoid osteoporosis” 30 Minutes: This is what American Heart Association recommends daily. Olson: “Thirty minutes seems to be the tipping point where you begin to see not just health benefits but fitness benefits like reduced weight and increased stamina as well,” and other advantages include cancer prevention, a lower risk of type 2 diabetes, and a healthier cholesterol profile. Olson, on exercise pace for improvements: The 30 minutes can be a moderate pace, brisk but sustainable. -So probably like a jog vs running a sprint. International Journal of Obesity study published earlier this year: pushing hard for the full half hour may lead to even greater weight loss by dulling your appetite. **Or rather by burning more calories! Same as if you add weights to your exercise. 60 Minutes: Olson: 1 hour a day at moderate pace = secret to substantial, long term weight loss; doesn't have to be all at once, can be with different exercises and activities “You can accumulate minutes throughout the day doing many different exercises and activities, including some resistance training,” she said. “And if you go at a higher intensity you can cut back to 45 minutes daily.” Harvard study: especially for middle-aged and older women who are close to their ideal weight 90 Minutes: Studies suggest: may be required for weight loss or maintenance if you are obese or have lost a lot of weight and have "stubborn metabolism" Olson: Longer exercise sessions should be performed at lower intensity to prevent injury and burn out, especially if have a lot of extra weight; break up workout into shorter, more manageable sessions, should yield same results as one marathon session (via "Why 6 Seconds of Exercise Can Be as Worthwhile as 90 Minutes")