If you had a choice, would you exercise really hard for a few minutes or moderately for 45 minutes?  Pressed for time, you would probably select the former.  According to a recent study, the two options - high-intensity interval training (HIIT) and endurance training - yield some of the same health and fitness benefits.

Now you may be wondering if the rise of HIIT signals the demise of endurance training.  Rest assured, both approaches are here to stay.  For a recent article in the Washington Post, lifelong mind-body fitness enthusiast Gabriella Boston explored the health and fitness benefits associated with HIIT and endurance training, whether or not HIIT training is appropriate for everyone, and if there is an ideal weekly ratio of HIIT-to-endurance training.

When she consulted fitness professionals and a sports medicine doctor, she was directed to a study by researchers at McMaster University in Ontario.  The study looked at sedentary individuals, not athletes with sport-specific goals, and focused on health indicators such as insulin sensitivity and cardiorespiratory fitness (the body's ability to supply oxygen-rich blood to the muscles and for the muscles to use that blood for movement). "The study focused on health intervention. How can we get [sedentary] people into a regular exercise routine?" said Pete McCall, spokesperson for the American Council on Exercise.

As Boston highlighted, lack of time is often cited as a reason that so many of us (about 60 percent) fail to get regular exercise.  Therefore, for the majority of Americans, a shorter, more efficient routine could be an attractive solution. 

The study concluded that 30 minutes of interval training, consisting of 10 minutes to warm-up, 10 minutes of high-intensity intervals, and 10 minutes of cool-down, had the same health benefits as 150 minutes of moderate endurance activity for individuals who are just starting out on a fitness regime.  It is important to note that those who are sedentary and just starting a fitness program are the most vulnerable to cardiac events, which can be brought on by high-intensity interval training.  Therefore, members of this population should definitely see their doctor for an evaluation before starting a new fitness routine.

Next, Boston explored the benefits of HIIT for those who are already engaged in a fitness routine.  "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 a measure of the maximum volume of oxygen that an athlete can use per minute while lactate threshold is the point at which lactate, a waste product resulting from the body’s conversion of nutrients to energy, builds up faster than it can be removed from the blood.  "The best athletes have the highest VO2 max," he says.

However, when it comes to HIIT vs. endurance training, it is never an either/or situation.  The ration depends on the athletic activity and it’s specific demands.  Most runners, for example, will do high-intensity interval training, working at more than 90 percent of their max heart rate, to increase power and speed, but they obviously also do long runs too, says Hryvniak.

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), while a tennis player might train with 30- to 45-second intervals, says Ben Fidler, fitness director at Sport&Health on Capitol Hill in Washington.

Fidler, who does high-intensity intervals as part of his own routine, says it is 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."

High intensity training creates significant stress on muscles and demands sufficient nutrition, sleep and recovery to heal muscles and avoid overtraining syndrome.  Overtraining syndrome is an imbalance that can be illustrated in a simple equation: Training = Workout + Recovery. The full spectrum of overtraining syndrome includes hormonal, nutritional, mental, emotional, muscular, and neurological imbalances.

Unlike HIIT, you can train aerobically for endurance, 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 at an easy to moderate level, training at 40 percent to 60 percent of your maximum heart rate, and then, as you get fitter, move into a moderate-to-challenging range at about 70 percent of your max heart rate.  If you would like to learn more about finding your target heart rate, see my article, “Finding Your Target Heart Rate.”  (insert link here).

It is also important to be sport- and goal-specific when figuring out your training routine.  If you are 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 is what it becomes good at - not 90 minutes of steady-state endurance 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/endurance training zone is also called “the fat-burning zone,” which means that the body is using fat for fuel, Hryvniak says. Therefore, it is clear that endurance training can be beneficial for weight loss.  Studies also show that HIIT is useful for weight loss, as the post-exercise metabolic rate is higher after HIIT than after endurance training.  In other words, HIIT and endurance training are complimentary and that the ideal ratio is really sport and goal specific.

Fitness experts recommend not just doing these two but also adding strength, balance, mobility and stability into your routine.  For example, add resistance training for strength and stability as well as yoga for mobility, core, mind and balance.

Boston’s fitness experts all suggest varying 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."