With High Intensity Interval Training (HIIT), which consists of short bursts of intensive activity followed by short periods of recovery, fitness experts say the harder the push, the greater the reward.
HIIT can blast calories, build muscle and boost endurance with impressive efficiency in just 20 minutes a day, but the catch is finding the right level of intensity outside the comfort zone, fitness trainers say.
Sean Bartram, author of the book "High Intensity Interval Training for Women," said to find that level people should think about what it is like being chased by a rabid dog.
"It's just below that," he said. "To gain maximum benefits you have to push your body to a place that's almost uncomfortable."
The American College of Sports Medicine predicts HIIT will be a top fitness trend in 2015. Bartram said people are drawn to it for its efficiency and almost endless variety of exercises.
The bursts can be sprinting or spot jumps and the recovery can be rests or slower paced movements, he explained.
"You could alternate 30 seconds of sprinting with 30 seconds of walking, or you could engage in a series of bodyweight exercises, such as push-ups, doing each for 30 seconds with 10 seconds of rest in between," he said.
Dr. Michele Olson, a professor of exercise science at Auburn University at Montgomery, Alabama, said it's not high intensity unless the heart rate is elevated to near 90-plus percentage of its maximum.
"Many people think they are engaging in HIIT but they are really doing traditional interval training, where the heart rate is around 75 to 85 percent of max," she said.
Maximum heart rate is about 220 minus age, according to the American Heart Association.
Olson said that if done properly, HIIT can increase the effectiveness in losing abdominal fat and prompt favorable changes in cholesterol and insulin levels.
"There is research showing that you can cut your exercise time nearly in half," she said.
About 20 minutes of HIIT can reap similar benefits of doing 35 to 40 minutes of moderate, steady-state cardio, she added, noting the training level must be intense.
Hayley Zawadzki, personal training manager at New York Health and Racquet Club fitness centers, suggests that anyone starting HIIT should have a fitness analysis.
"If you have a history of high blood pressure or medications, you cannot push to the absolute max," she said.