It sounds too good to be true: Lose weight, while cutting your workout time in half.
But researchers are finding there may be a way for more people to make that happen. The old idea of interval training -- workouts involving sprints followed by periods of slower activity -- may be a more effective way to lose weight than most have realized.
Sprints play a mind-body trick that can work to your advantage, she said.
"We use interval training to keep it fun and also to increase the intensity without people paying attention to intensity," Kennedy said.
A study at the Australian University of New South Wales backs the theory that sprints are more effective.
It looked at two groups of people. One regularly rode a bike at a steady pace for 40 minutes at a time. The other rode for just 20 minutes, but alternated between eight-second sprints and 12-second periods of rest.
The group that biked at a steady pace lost an average of two pounds, while the sprinters lost an average of six pounds.
Scientists said they aren't sure exactly why it works, but they theorized that the sprints may also affect hormones that regulate fat cells.
Melissa Burns, who takes the Baylor spinning class, said it's been a great way to jump start her workouts.
"You work harder, but I guess you get some recovery time after, which makes it easier -- or it feels easier to get a good workout," she said.
Trainers say you can use interval training with almost any kind of aerobic exercise, including biking, running, swimming and jumping rope.