Sep 18, 2007

Q&A: "Training Zones" and Calorie Burn

Q: How do I know the heart rate zones and calorie counters on aerobic machines are accurate?

Simple…they aren’t. The numbers that you see on a typical cardiovascular machine related to “Training Zones” for heart rate and “Caloric Expenditure” should be viewed as guides. They are helpful in gaining some understanding (especially for beginning exercisers) as to where to start, how much effort is necessary for improvement, and what the resultant product of the exercise session is. However, in the long run it will most likely be detrimental (or frustrating, at its least) for an exerciser to plan or base his/her workouts on these numbers.

Let’s back up for a moment and review Exercise Physiology 101. Heart Rate is used as a guide to measure exercise intensity as it closely mimics oxygen consumption (which is held as the gold-standard but impractical to measure outside of the laboratory). There are currently several equations that are utilized to estimate where an individual’s optimal heart rate zone is for maximum training effect. Generally, the equation used on many cardio machines on the market is the Target Heart Range formula (220-Age x 50% and 90%). Again, while this is a good start, it often under or over estimates the correct range by as much as 15 beats/minutes (bpm). There are many variables which can effect the final decision as to what is the appropriate range, such as age, gender, exercise history, goals, medications, health concerns, etc. Ultimately the above formula is a good range for cardiovascular improvements, but utilizing tools such as the Rate of Perceived Exertion or Talk Test are helpful in adapting the range more specifically to your current fitness level. For example, at the lower end of your training zone you should be able to carry on a conversation having only to catch your breath every few sentences while at the upper end having difficulty holding a conversation at all.

Caloric Expenditure—determined by mL of Oxygen consumed per kilogram of bodyweight per minute (mL/kg/min)—is a bit more involved procedure. Again, outside the laboratory this is difficult to determine and is affected by all of the factors listed above. In addition to this there are the components of weight, body fat percentage and adaptation to activity. Cardiovascular machines cannot account for all of these factors. Ultimately they will provide the user with some sort of estimate. But if it is important for you to determine a more accurate number (i.e. for goal achievement), you may want to consult a trusted Personal Trainer/Exercise Physiologist who can aid in that process.

Written for SB Fitness Magazine Vol.3 Is.3 (Click here to visit site)

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