Exercise has had a Goldilocks problem, with experts debating just how much exercise is too little, too much or just the right amount to improve health and longevity. Two new, impressively large-scale studies provide some clarity. In the broader of the two studies, researchers ... found that, unsurprisingly, the people who did not exercise at all were at the highest risk of early death. But those who exercised a little, not meeting the recommendations but doing something, lowered their risk of premature death by 20 percent. The sweet spot for exercise benefits, however, came among those who tripled the recommended level of exercise, working out moderately, mostly by walking, for 450 minutes per week, or a little more than an hour per day. Those people were 39 percent less likely to die prematurely than people who never exercised. At that point, the benefits plateaued, the researchers found, but they never significantly declined. The other new study of exercise and mortality reached a somewhat similar conclusion, [and found that] if someone engaged in even occasional vigorous exercise, he or she gained a small but not unimportant additional reduction in mortality.