Sunday, March 4, 2012

A little bit on MET values & VO2 Max


Ever concerned with caloric burn, I discovered that heart rate monitor calorie counts are only accurate when there is a consistent and measurable relationship between heart rate and oxygen uptake. That means exercises that are aerobic in nature and that are performed at intensities between 40% of VO2 max and the lactate threshold.  Insanity does not meet these criteria.

A MET refers to the ratio of the work metabolic rate to the resting metabolic rate. One MET is defined as 1 kcal/kg/hour and is roughly equivalent to the energy cost of sitting quietly.  A MET also is defined as oxygen uptake in ml/kg/min with one MET equal to the oxygen cost of sitting quietly, equivalent to 3.5 ml/kg/min.  It was difficult, but in my research, I found a reliable MET value for HIIT and an equation for caloric expenditure.  Traditional HIIT requires around 12.5 METs.  This value does not account for the 10 % afterburn, often referred to as Excess Post-Exercise Oxygen Consumption (EPOC).  Insanity is not traditional HIIT, but even harder, so the value could feasibly be higher.

Therefore, an accurate equation for calories burned is METs x 3.5 x (weight in kg)/200 = kcal/min burned.

VO2 Max peaks at age 18 until age 25, and from then, it declines by roughly 1% every year.  Even though cardiovascular fitness obviously influences VO2 Max, genetics heavily influence it, too.  The capacity of your circulatory system to deliver oxygenated blood to your muscles and also the specific physiology of your muscles are both genetically predetermined to a certain extent.

I tested my VO2 max here: VO2 Max Calculator, utilizing the resting heart rate, step, and 1.5 mile run tests.


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