If you had a choice, would you exercise really hard for one minute or moderately for 45 minutes?
Pressed for time, you probably picked the first option. According to a recent study, the two options -- high-intensity interval training (HIIT) and endurance/aerobic training -- yield some of the same health and fitness benefits.
How is that possible?
Is the rise of HIIT the end of endurance training?
As it turns out, it's a bit of an apples-and-oranges situation.
First off, what do we mean by "health and fitness benefits"?
Second, is the one-minute, all-out interval appropriate for everyone?
And finally, is there an ideal weekly ratio of HIIT-to-endurance training?
We asked two fitness professionals and a sports medicine doctor to help clear things up.
HIIT for beginners
To be clear, the study, by researchers at McMaster University in Ontario, looked at sedentary individuals, not athletes with sport-specific goals, and it focused on health indicators such as insulin sensitivity and cardiorespiratory fitness (the body's ability to supply oxygen-rich blood to muscles and for the muscles to use that blood for movement).
It was not about whether you should skip the prep run for your 10K race and do a minute of intervals instead. You shouldn't!
"The study focused on health intervention. How can we get (sedentary) people into a regular exercise routine?" says Pete McCall, spokesman for the American Council on Exercise.
Lack of time is often cited as a reason that so many Americans -- about 60 percent -- don't exercise regularly. So a shorter, more efficient routine could be an appealing solution.
"You can't tell me you don't have just a few minutes every week to exercise," McCall says.
The study concluded that 30 minutes of interval training (really just 10 minutes of true intervals featuring all-out sprints, plus 20 minutes of warm-up and cool-down) had the same health benefits as 150 minutes of moderate aerobic activity -- for individuals who are just starting out on a fitness regime. (This population is the most vulnerable to cardiac events, which can be brought on by high-intensity interval training. so, as always, please see a doctor for an evaluation before starting a new fitness routine.)
Building VO2 max
But for those who are already in a routine, what are the benefits of high-intensity intervals?
"With athletes, like everyone else, it improves VO2 max and lactate threshold," says Dave Hryvniak, a doctor with University of Virginia sports teams.
VO2 max is the maximum amount of oxygen the body delivers to working muscles per minute; lactate threshold is the point at which lactate (a waste product from energy conversion) builds up faster than it can be removed from the blood.
"The best athletes in the world have the highest VO2 max," he says.
But it's never an either/or when it comes to HIIT and aerobic training, Hryvniak says. It depends on the sport and the specific demands of that sport.
Runners -- even long-distance runners -- will do high-intensity intervals (working at more than 90 percent of their max heart rate) to increase power and speed, but they obviously also do long runs, he says.
The type and length of intervals is sport-specific. For example, a football player might need to do 10-second intervals (short but very intense bursts of power), and a tennis player might need to do 30- to 45-second intervals, says Ben Fidler, fitness director at Sport&Health in Washington.
Fidler, who does high-intensity intervals as part of his own routine, says it's important to remember that the body needs lots of time to recover after high-intensity intervals. "You can only do HIIT 15 to 20 minutes a few times a week," Fidler says. "It's really hard on the body."
Adds McCall: "High-stress exercise means high stress for the muscle tissue, and if you don't get the right nutrition, sleep and overall recovery, you could put yourself at risk for overtraining syndrome." This includes depression and feeling tired all the time yet unable to sleep at night.
Unlike HIIT, you can train aerobically (at a lower heart rate) every day of the week.
"Endurance days can also help you recover from the high-intensity days," Hryvniak says.
As with any training program, though, you should start easy to moderate (40 percent to 60 percent of your max heart rate) and then, as you get fitter, move into a moderate-to-challenging range (70 percent of your max heart rate).
It is also important to be sport- and goal-specific when figuring out your training routine.
If you're training for a 10-miler, you will have to put the time in. For example, if you figure the race will take you 90 minutes, you need to be on your feet for that amount of time during training.
"The body is an adaptive machine," Fidler says. "It will respond to whatever you put it through."
In other words, if you put it through 15 to 20 minutes of high-intensity intervals, that's what it becomes good at -- not 90 minutes of steady-state aerobic work.
"Your body won't know what to do after the 15 to 20 minutes of HIIT," he says. "But when you are working on steady-state cardio for a longer period of time, the body adapts to that."
The aerobic training zone is also famously known as the fat-burning zone, which means the body can use fat for fuel, Hryvniak says. So for weight loss, aerobic training can be beneficial. But so can HIIT, it turns out.
"Studies show that the post-exercise metabolic rate is higher after HIIT," Hryvniak says.
In other words, it seems that these two -- HIIT and endurance training -- go hand in hand and that the ratio really is sport- and goal-specific.
Variety of training
Our fitness experts recommend not just doing these two but also adding strength, balance, mobility and stability into your routine: yoga for mobility core, mind and balance; as well as resistance training for strength and stability.
They all say to vary your routine at least every few months if you want to continue to see improvement.
"There is no one way of doing it," McCall says. "But we do know that doing nothing at all -- no regular exercise at all -- will take years off your life."