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Intervals vs Cardio

By David DiFabio

Research has show that interval workouts can potentially burn more calories than a steady-state cardio because of the increased intensity with each interval. If designed with proper work to rest ratios in mind, an interval workout will allow for greater total work (calorie expenditure). Potentially, the built-in rest periods will allow you to push harder and enhance the metabolic systems that will help you buffer lactate. Furthermore, oxygen consumption can remain elevated for a longer period of time after an interval workout. This is commonly known as the "after-burn" where the body is replenishing the fuel and enzymes, which were depleted during the workout. Again, this translates into greater caloric expenditure. How can you use this knowledge to your advantage? The easiest and most convenient way is to select the random or hill profile the next time you get on your favorite piece of cardio equipment instead of just going at a constant speed or incline. However, if the work/rest ratios aren't designed specifically for you, it could result in lower power output.

However it is best to customize your intervals by using heart rate ranges. If you don't already have a heart rate monitor, it is worth the $50 investment for a basic model. HR monitors can be bought at just about any sporting good store. If you don't have a monitor you can always use the old fashion manual method which requires you to count your pulse in your wrist or neck.

Now, you must estimate your age-predicted maximum. You may be familiar with formulas such as 220-age (males) or 226 – age (females). Throw those out. They are outdated. Both males and females should use this one: 208 – 70% of your age. So let's say you're 30 years old. That would look like this:

208 – (.70)30 = 208 – 21 = 187. Therefore, based on this formula it is predicted that 187 beats per minute (bpm) is the maximum heart rate a 30 year old would be able to attain. Now you need to calculate your hear rate reserve (HRR). To do this, simply subtract your resting pulse (as counted in the morning upon awakening) from your age-predicted maximum HR. Let's assume our 30 year old has a resting pulse of 50 bpm. His HRR would be 137 bpm.

Before I proceed, I need to tell you a little about resting pulse. The American average is between 75 and 85 bpm. Anything over 100 bpm or below 40 bpm at rest could be cause for concern (there are exceptions to every rule) and you should consult your physician. The better shape you're in, the lower your resting HR will be. Some elite endurance athletes have resting heart rates as low as 40 bpm. You should expect your HR to be elevated during exercise, cool down, warm-up, and recovery periods. HR can be affected by stress and drugs/medication.

Your working and recovery heart rate ratios for your interval workouts will be determined based on percentages of your HHR. If you're new to exercise you will use conservative percentages. If you already workout out 3 times/week at a moderate intensity you can use moderate percentages. If you workout 5 or 6 times/week at a moderate to high intensity, you can be more aggressive.

Now back to our example. Our 30 year-old has a resting pulse of 50 bpm. Based on the info above, we know that's pretty low thus he's probably in very good shape. Let's say he currently works out at a moderate to high intensity 5 days/week. So he can use an aggressive HR prescription. Typically, prescriptions for a cardiovascular workout consist of a HRR percentage range of 50% (sedentary/elderly participants) to 90% (elite athletes). Based on the info we have for this 30 year-old let's use a range of 75% to 85%.

So we'll take 137 (HHR for our 30 year old) and multiply it times .75 and .85 to helps us determine a HRR range of 102 to 116. To get a "working" interval range that we can use we have add our 30 year-old's resting pulse (50 bpm) back into the range. (102 + 50 & 116+50) = 152 bpm to166 bpm. That is a very important step to remember. So for this 30 year-old, his heart rate should reach a level between 152 and 166. Once his HR reaches that level due to a 30 to 90 second sprint/run, he should slow down (walk/jog) until his hear rate comes back down to 50% or 60% of HHR (101 to 111 bpm in our case). Our 30 year old should repeat this (work to rest) intervals for 20 to 30 minutes, 3 to 5 days/week. As he becomes more fit, the work to rest ratios will automatically take care of itself as long as HR is tracked. As he becomes more fit, it will take a greater intensity to achieve the desired working HR. Furthermore, his recovery period will "speed up". This means his HR will come back down to recovery levels (50 to 60% of HHR) a lot sooner during his walk/jog period. Thus, as he becomes more fit his rest periods will automatically shorten. After 4 weeks of training, resting pulse and HHR reserve should be calculated to compensate for an improved fitness level. These new values should be used to calculate new work to rest intervals.

One final thought. Do you hate running? Are you not able to run? Would you rather use a cross-trainer, arc-trainer, or even a bike? No problem. This interval method can be used on any piece of cardio equipment. Select the manual program, this will allow you to manipulate resistance, grade, RPMs, and/or strides per minute as you go along.

Compared to steady-state cardio, intervals have the potential to burn more calories in the same amount of time or the same amount of calories in less time. Try it out and see the results for yourself.

About the Author:

Dave DiFabio MA, CSCS, USAW, is the Founder of Team Speed Fitness. He is also a Strength and Conditioning Specialist and Professor at Rutgers University. Dave is also available for online personal training.

Dave has 12 years of training experience and holds a Masters and Bachelors in Exercise Physiology. He is certified by the National Strength & Conditioning Association and by USA Weightlifting. Dave’s clientele includes collegiate and high school athletes, adults and children, and those with special needs or medical concerns. Dave is a regular contributor to Men's Fitness Magazine and has coauthored two research studies dealing with antioxidant supplementation and overtraining. The results of the above studies were presented at the American College of Sports Medicine's 52nd and 53rd Annual Meetings. Dave can be reached via his website TeamSpeedFitness.com. Be sure to view the free “Food for Fitness” videos to learn how to make intelligent, healthy choices at the supermarket.