About BMI
BMI stands for Body Mass Index, a statistical term derived from height and weight.
It is closely linked to body fat and health outcomes. Over 50 organizations,
including the US Government and the World Health Organization, have adopted
BMI guidelines. BMI is inversely related to fitness, meaning that the higher your
BMI, the less likely you are to be fit. Every time your body fat monitor reads your
weight and calculates your body fat, it also calculates your BMI. Along with your
weight and your body fat measurements, the BMI reading gives you yet one more
tool to monitor your health and fitness.
General guidelines for BMI are as follows:
BMI less than 19: underweight
BMI 19–25: healthy weight
BMI 25–30: overweight
BMI over 30: obese
About BMI Levels
In order to make your body fat and body water readings more accurate, your
monitor automatically calculates a BMI level for you, based on the personal data
you have entered, as well as measurements the scale takes. Why is that important?
People with different BMIs have differences in muscle mass and body water levels.
Do not be alarmed if you do not see rapid changes to your category level:
generally, your level will change as you lose weight and become more fit.
These changes happen gradually, though, and you may not see them reflected
for a few months of consistently following a diet and exercise regimen.
BMI/Fitness Levels
1
2
3
4
5
Less Fit More Fit
L3 is the “normal” mode and is often selected at the start of a training/weight loss
program. Most people fall into this category. Its activities are characterized by:
• low level aerobics
• limited physical activity: less than 2 times/week
• less than 20 minutes per activity
L4 is used by people who have improved overall wellness and fitness:
• moderate daily exercise: 20 minute workouts, 5 times/week
• activities: cycling, jogging, brisk walking, raking leaves, tennis, aerobics
L5 is used by highly active individuals whose workouts are based both on
endurance and strength over an extended period of time:
• daily workouts to include the activities below
• 5-10 minute warm up; several 20-30 minute workouts per week dedicated to
muscular strength (often weight lifting), muscular endurance (pushups, sit-ups,
weight training for all major muscle groups), cardio respiratory endurance
(jogging, swimming, rope-jumping, rowing, racquetball); 10-12 minutes of
stretching; 5-10 minute cooldown
Weight and Body Fat
How does it work?
While body fat can be measured in many ways, the method used in your scale
is bioelectrical impedance. This indirect method of determining body fat starts when
a safe and very low electrical current is sent through the lower half of the body.
The electrical current flows more quickly through water and muscle than it will
through bone and fat. The scale measures the speed of the current. Based on this
number, the scale estimates body fat using a multi-step, mathematical formula.
Is it accurate?
Measurements of body fat tend to fluctuate a lot more than simple weighing,
and different methods of estimating body fat yield very different results. Just as
different scales give different results, different body fat analyzers can provide very
different body fat estimates. Even with the same scale the numbers will vary because:
• Weight loss tends to produce substantial, continuous, and unpredictable changes
in body water content. Because body fat analysis is determined by water content
in the body, results can vary considerably from day to day.
• Hydration status affects body fat results. If you’ve just worked out, there is less
water for the electrical current to flow through. This may result in a higher body
fat result. In the same way, if you measure your body fat after drinking a lot of
fluid, it may appear that body fat is lower than it really is.
• Skin temperature can have an influence also. Measuring body fat in warm humid
weather when skin is moist will yield a different result than if skin is cold and dry.
• As with weight, when your goal is to change body composition it is better to track
trends over time than to use individual daily results.
• Results may not be accurate for persons under the age of 16, or persons with
an elevated body temperature, diabetes or other health conditions.
What you need to know!
• Percent body fat refers to the number of pounds of fat divided by your total body
weight and multiplied by 100.
• During weight loss, percent body fat doesn’t appear to be reduced as quickly
as expected because total weight loss and total body fat are decreasing at the
same time (for a more detailed explanation, see next section).
• Weight loss in the form of body fat and lean tissue (muscle) is common, and is normal.
• To minimize the loss of lean tissue, include regular physical activity, especially
strength training, in your weight-loss plan.
Why do I lose weight but my body fat percentage doesn’t change much?
Most body fat monitors show body fat as a percentage only. This body fat
monitor shows you not only a percentage but the actual number of body fat
pounds (in fact, this is the measurement you see after your weight is displayed).
Why is that important? When you lose weight, both the numerator (pounds of body
fat) and denominator (total body weight) go down, so when it’s calculated as a body
fat percentage, the number can be small. For example, a person may weigh 200
pounds and have 40% body fat (= 80 pounds of body fat). He/She loses 20 pounds,
but the body fat has only dropped 4% to 36%. That 4% of body fat was 16 pounds
of fat – a very significant amount! So do not be overly concerned if you do not see
the percentage change quickly as you are losing weight: monitor the absolute
number of body fat pounds lost. Remember, to minimize the loss of lean tissue,
include regular physical activity, especially strength training, in your weight-loss plan.
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