Two of the fundamental truths about exercise are: 1) If you want to build muscle, workout with weights. 2) If you want to burn fat and improve cardiovascular health, aerobic type exercise is the answer.

The biggest debate about cardio is how long and how intensely you need to exercise to get results. 15 minutes? 30 minutes? An hour a day? Should you be walking, jogging or sprinting? The answer depends on your ultimate goals.

The American College of Sports Medicine (ACSM) and the American Heart Association (AHA) released updated guidelines in 2007 that said; "To promote and maintain health, all healthy adults aged 18-65 yr need moderate-intensity aerobic physical activity for a minimum of 30 min on five days each week..." The key part of that statement is "moderate-intensity," which AHA says is equivalent to a "brisk walk" that "noticeably accelerates the heart rate..."

If you don't have that much time, the AHA guidelines go on to say, "vigorous-intensity aerobic activity for a minimum of 20 min on three days each week." Vigorous-intensity is described as "...jogging, and causes rapid breathing and a substantial increase in heart rate."

People who follow those recommendations tend to be more fit and live longer than their sedentary peers. But a researcher at McMaster University in Hamilton, Canada, wanted to see just how little cardio type exercise you could do and still see a benefit. So Mark Rakobowchuk and his group recruited 20 healthy untrained subjects in their mid-twenties and had them perform 6 weeks of low-volume sprint interval training (SIT) or 6 weeks of traditional high-volume endurance training (ET).

The SIT group performed four to six "all-out" sprints for 30 seconds at a time. In-between each sprint, they would rest for 4.5 minutes. The SIT group exercised like that three days a week.

Meanwhile, the ET group did 40-60 minutes of cycling at 65% of their VO2 Max five days a week.

VO2 Max is defined as: "The maximum capacity of an individual's body to transport and utilize oxygen during incremental exercise."

The study lasted for 6 weeks. When it was finished, the SIT group had exercised an average of 45 minutes total, not counting rest time. The ET group exercised an average of 1,500 minutes during the same period. The differences in time were dramatic. The results were even more incredible.

This is what the study concluded, "...popliteal artery distensibility was improved in both groups to the same degree."

What that means is the arteries of both the SIT and ET groups benefited equally. Constricted arteries are a major cause of cardiovascular disease. Learning that short bursts of very high-intensity training can help the elasticity of arteries is a big deal.

It is tough to get someone to do 30-60 minutes of cardio five days a week. Learning that there's an option that's far less time consuming may mean more people will make an effort. Yes, the exercise has to be much more intense, but for busy people, it may mean the difference between getting some heart helping cardio in or skipping the workout entirely.

In the decade since we wrote this article, researchers have found that interval training (running sprints) is also a better way for people to drop fat. In study after study, interval training was the most effective cardio exercise any group of people could do.

A word of caution here. It is possible to cross the line and get too much cardio exercise. Warning signs include physical soreness that won't go away. Your workouts may seem to get harder instead of easier over time, sleeplessness and general fatigue. Unless you're training for a marathon or extreme event, try and keep it under an hour and a half a day. More than that and you risk losing muscle as your body burns it for energy.

When you're ready, do what you can manage consistently.

Are you there yet?

SPECIAL UPDATE!

Since we wrote this column, this type of training (Interval Training) has proven to be incredibly beneficial. Click Here for our full update on Interval Training and how to build your own program.

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7/13/2008
Updated 8/7/2010
Updated 5/19/2019