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Interval Training: Burn More Calories in Less Time, Part 1

The primary reason why Americans say they don’t work out is a lack of time. Of course, they also report watching three hours of television each day. So just how are you supposed to be able to juggle your full-time job, part-time job, family, and fitness on top of it all?

Priorities are always a good answer, but even those dedicated to working out and staying fit don’t always have the time to fit their workout into a busy day. Fortunately, there is a time-efficient alternative, and you don’t even have to leave home to do it (unless you want to).

Interval training is a type of workout in which training intensities vary between high (usually anaerobic) and low (aerobic). The overall results include a higher calorie burn during a shorter session, an improvement in performance (speed, power, and endurance), an increase in aerobic power, higher tolerance to lactic acid, and a higher caloric burn during and after the session due to “excess post-exercise consumption” or EPOC. Such a workout will improve both aerobic and anaerobic systems depending on the intensity and duration of the designed interval and recovery periods.


When you first start exercising, your body requires more oxygen than is immediately available. You may feel “winded” until your oxygen intake matches that which is required by your exercising muscles. This period of about 10 minutes is called the “oxygen deficit state” because your body is trying to catch up to the oxygen and fuel requirements. If you continue to exercise beyond this 10 minutes, you reach a point when your breathing feels like it matches your exertion level, and you have reached your “steady state” of exercise.

After you stop exercising, you continue to breathe faster than at rest as your body recovers and repays the oxygen / fuel debt it has run up. This phase is called excess post-exercise oxygen uptake, or EPOC. You are burning more calories than at rest during this recovery phase. The greater the intensity and duration of the workout, the greater the oxygen deficit, thus the greater the EPOC to recover. In other words, you will burn more “recovery calories” after your workout.

Energy Systems of the Body

Knowing which energy system is being predominantly utilized during exercise is important in achieving specific goals. For example, if Officer Gonzales wanted to improve his speed, he should not run long distances slowly because his goals would not be realized. The intensity of exercise and the type and length of the rest intervals would have to be specific to the energy system he wanted to improve or train.

For street cops, it is important to train all the metabolic systems for a lifetime of good health and satisfying leisure time with family. But more important, they need to train for survival when an officer is the only one in between an MMA wanna-be and prison; that criminal who prides himself on his tolerance to pain may be willing to die before going back.

The energy systems of the body are all in use during physical activity, however, a person’s intensity and duration of exertion determines which one is predominantly used at any given time. The goal of all three systems is to produce and use the energy found in adenosine triphosphate, or ATP.

Each system, however, produces ATP at a different rate and in different amounts. Because of these benefits and limitations, each system is used for different levels of exertion. The three systems are the phosphagen system, glycolysis (fast and slow), and the oxidative system.

Phosphagen System

The anaerobic system used during the first 10 seconds of intense activity is the phosphagen system, which produces ATP very quickly but in small amounts—hence it is good for only those first seconds of a sprint or a fight. In order for an officer to train this system to improve his start-up acceleration or forceful strikes and takedowns, he would need to incorporate short bouts of highly intense exercise, with enough recovery to replenish the ATP (3 to 5 minutes) and creatine phosphate (8 minutes).

Aerobic metabolism will assist in replenishing these phosphagen substrates more quickly, so an active aerobic recovery is preferred over passive (walk rather than stop after short sprints). Work-to-rest ratios are generally in the range of 1:12 to 1:20 when training the phosphagen system, and exertion levels are 90-100% of maximum power. Adequate recovery in between is of utmost importance because if not, the next work interval will be performed while fatigued, and results will wane.

An example of incorporating interval-style training for this energy system might include performing the clean-and-jerk exercise repeatedly for 10 seconds, then walking or stationary cycling at an easy pace for eight minutes, and repeating this cycle for a set amount of time.

Another example might include a cycle of boxing as hard as possible for 10 seconds then jogging for 2 minutes. Start-up power can be trained with very short sprints (up to 10 seconds), then walking the rest of the track back to the starting line for the next short sprint. Plyometrics are also excellent exercises for training the phosphagen system.

Kathleen Vonk has been a certified police officer in Michigan since 1988, currently with the Ann Arbor Police. She designed and implemented the Police Wellness Instructor Course for the Michigan Commission on Law Enforcement Standards, for which she is a subject matter expert, consultant and instructor-trainer. She can be reached at

Published in Law and Order, Aug 2009

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