Stephen J. Carter, a cardiovascular physiologist at the Indiana University Bloomington School of Public Health, said that shorter, more intense workouts are better than longer, less intense workouts at lowering the risk of cardiovascular disease and reducing overall mortality rates.

One of Mr. Howell’s favorite full-body, no-equipment, time-efficient workouts is simple and can be scaled to any fitness level or ability.

The workout is: Five body weight squats, five push-ups and a 30-second plank — repeated six times, resting for no more than 30 seconds between rounds. If you can’t do a push-up on the floor, do it against a countertop or a stable bench. You can modify the plank by putting your knees on the floor or doing a standing plank by placing your forearms on the wall.