Another popular fitness belief bites the dust: According to several recent studies, when it comes to exercise, more isn't necessarily better. In fact, shorter workouts may be the key to better health and fitness. So why is shorter better? It has to do with how likely you are to stay with a fitness regimen and how hard you actually work while exercising.

A Brown University study, for example, concluded that people who were just beginning a fitness program were more likely to stick with a shorter workout regimen, while another analysis by the University of New Hampshire at Durham found exercisers who chose two shorter treadmill sessions over one long session worked harder. And the payoff from that harder workout was a better boost in their aerobic capacity and endurance.

Similarly, researchers at the University of Missouri found that 10 minutes of brisk walking or jogging was more effective than 30 continuous minutes. The shorter workouts more effectively helped to clear the arteries of triglycerides. Triglycerides can elevate the risk of a heart attack.

Yet more evidence supporting the benefits of a short workout comes from a Harvard School of Public Health study. It found that two 15 minute cardio workouts were as effective in reducing heart disease as a single 30 minute workout.