How Often Should You Work Out? Here's What New Research Says

You've got the number of days down. Now, how long do you need to buckle down for each day? Cruz recommends that "workouts last anywhere from 30 to 90 minutes." The range depends on the intensity of the workout. A rule of thumb: the more intense the workout, the shorter it should be.

For longer workouts, Cruz suggests splitting them up into 30 to 45 minutes of weight training, then finishing off with 20 to 30 minutes of cardio. If you're a bit squeezed for time, Cruz's go-to workout is a 30-minute circuit or high-intensity interval (HIIT) workout.