For fitness walking, you're going fast enough if you can speak a few words but don't have enough breath to carry on a conversation. Now kick it up a notch. Intersperse short bursts of power within your workout when it's hard to even speak at all.
This high-intensity interval training (H.I.I.T.), used by track and field athletes to improve times, is now being touted for exercise routines as a way to boost metabolism and blaze through calories.
If you're a walker, it might go like this: After a warm up of about five minutes, start alternating your exertion level between one-minute bursts of speed and two minutes of recovery.
"You get more bang for your buck," said Jackie McMahon, a fitness coordinator at the Bradenton YMCA.
"If you want to get fit more quickly, this is a good way to do it," she said.
According to the American Council on Exercise, most endurance workouts like walking, running or stair climbing are performed at moderate intensity of 5 to 6 on a scale of 0 to 10. The high-intensity intervals should take the exertion level to 7 or higher.
To compare, aerobics classes usually are pegged to about a 5 to 6 exertion level -- the high-intensity interval will push way beyond that, but only for a short burst of time.
"Interval training is very popular right now. It burns a lot of calories and increases the heart rate," said McMahon. "It almost gets into the anaerobic stage."
Anaerobic exercise, which pushes past the amount of oxygen available to the body, improves endurance and builds lean muscle.
The more lean muscle, the higher the calorie-burn when the body is at rest.
Interval training can be added to walking and running workouts and it's also being incorporated into exercise classes.
Many stationary bicycles and treadmills have built-in interval training programs.
Being a super-athlete isn't required. The amount of exertion will be individual -- a three-mile-per-hour pace could feel like high-level exertion to someone who is less fit while a seasoned runner might have to break into an all-out sprint.
That means adjust intensity as needed. In a class where everyone is doing two minutes of high-speed jumping jacks, it's OK to march in place.
"Interval training can be for anyone," said Jeff Lightburne, fitness and wellness coordinator at the G.T. Bray park recreation center.
"For instance, when you first start walking, you can throw in 30 seconds of fast walking, then take a minute to catch your breath. When you're more conditioned, you can do 30-second sprints, then 30 seconds to a minute when you don't run."
"This is also a way to break up exercise boredom," he said.
There is no single way to structure the sequences. Speed intervals might be 30 seconds to five minutes, bursts of six to eight seconds, or longer. Recovery periods should be equal to or longer than the speed intervals.
The most common mistake is making the recovery intervals too short, according to the American Council on Exercise.
One benefit for people in a hurry is that high-interval workouts can be completed much more quickly.
A good workout of four to five rounds of alternating between exercising intensely and taking the intensity down, along with a warm-up and cool-down, might take about 22 minutes.
The American Council on Exercise recommends that high-intensity interval training be limited to one to two times a week to reduce risk of injury, and used periodically for up to six weeks to enhance training rather than year-round.
Susan Hemmingway, Herald health correspondent, can be reached at firstname.lastname@example.org.