6. Explaining METS, Calories and Watts
When you exercise, your body burns fat and releases energy or power. METs
(Metabolic
Equivalents), Exercise Calories, and Watts are terms that measure the amount
of energy or power that is released.
What are METs (Metabolic Equivalents)?
METs, or metabolic equivalents, measure the rate of energy expended by estimating the
amount of oxygen used by the body. One MET is equal to the amount of oxygen used by
the body at rest. Everyone at rest expends energy at the same rate and uses the same
amount of oxygen for each kilogram (or pound) of body weight, regardless of age or
fitness level. One MET uses about 3.5 milliliters of oxygen per kilogram of bodyweight
per minute (3.5 ml/kg/min).
During physical exercise, MET levels increase because the body consumes more oxygen.
As oxygen is consumed, the body produces heat. Individuals utilize oxygen and expend
energy at different rates depending on their fitness levels. Each increase in oxygen of 3.5
ml/kg/min increases the energy expenditure by 1 MET. The individual able to process
more oxygen is more fit, and so can expend more energy and sustain a higher MET level.
The American College of Sports Medicine has published formulas to estimate the oxygen
cost of exercising at various work loads (watts) on treadmills, lower body cycles, upper
body cycles, and steppers, as well as while walking and running outdoors. MET levels can
be determined by simply dividing oxygen consumption in ml/kg/min by 3.5. The MET
level at which one exercises is
directly proportional to the amount of oxygen being
consumed, the amount of power (watts)
accomplished, and the amount of calories
burned while exercising.
MET charts have been developed by researchers to estimate the MET levels of domestic and
recreational activities. Each type of physical activity and intensity level is assigned a MET
value.
• Light-intensity activities are assigned values of from 1.1 to 2.9 METs
• Moderate physical activities are assigned values from 3 to 6 METs
• Vigorous activities are assigned values over 6 METs
These estimations are generalizations as to how many times individuals needs to
elevate their
metabolic rate (METs) to accomplish such activities.
METS And Cardiopulmonary Rehabilitation
METs are often used in prescribing exercise for patients involved in cardiopulmonary
rehabilitation. Cardiovascular medical experts and physiologists can correlate METs to VO2
max, a measure of maximal oxygen consumption and conditioning. A cardiac stress test
typically reports the max
imum MET level achieved by the patient and/or the MET level
achieved at the point the test
turned positive (often demonstrating ischemic changes in
the heart muscle and/or inappropriate arrhythmias). Cardiologists often ask therapists to
keep a patient below a certain MET level based
on this information from the cardiac
stress test. The Cardiologist will report, for example,
"ischemic changes at 10
METs/Heart Rate 128. Exercise at or below 9 METs."
On each type of cardiovascular exercise machine, a user must exercise at a different work
load (watts) to attain a consistent metabolic rate and a corresponding appropriate heart rate.
Cranking an upper body cycle at 100 watts will, for example, have a very different effect on
one’s metabolic rate and heart rate when compared to pedaling a lower body cycle at 100
watts. It is up to the clinician to set the appropriate workloads on each ergometer to achieve
the appropriate MET level.
EXPLAINING METS, CALORIES, & WATTS — 16 —
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