The body mass index (BMI), or Quetelet index, is a statistical measure which compares a person's weight and height. Though it does not actually measure the percentage of body fat, it is used to estimate a healthy body weight based on a person's height. Due to its ease of measurement and calculation, it is the most widely used diagnostic tool to identify weight problems within a population, usually whether individuals are underweight, overweight or obese. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing "social physics". Body mass index is defined as the individual's body weight divided by the square of his or her height. The formula universally used in medicine produce a unit of measure of kg/m2. BMI can also be determined using a BMI chart, which displays BMI as a function of weight (horizontal axis) and height (vertical axis) using contour lines for different values of BMI or colours for different BMI categories.

Some argue that the error in the BMI is significant and so pervasive that it is not generally useful in evaluation of health. Based on body mass index calculator research, University of Chicago political science professor Eric Oliver says BMI is a convenient but inaccurate measure of weight, forced onto the populace, and should be revised, so should the BMI calculator.

The medical establishment has generally acknowledged some shortcomings of BMI. Because the BMI is dependent only upon weight and height, it makes simplistic assumptions about distribution of muscle and bone mass, and thus may overestimate adiposity on those with more lean body mass (e.g. athletes) while underestimating adiposity on those with less lean body mass (e.g. the elderly).

A 2005 study in America showed that overweight people had a similar relative risk of mortality to normal weight people as defined by BMI. In an analysis of 40 studies involving 250,000 people, patients with coronary artery disease with normal BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the "overweight" range (BMI 25–29.9). In the intermediate range of BMI (25–29.9), BMI failed to discriminate between bodyfat percentage and lean mass. The study concluded that "the accuracy of BMI in diagnosing obesity is limited, particularly for individuals in the intermediate BMI ranges, in men and in the elderly... These results may help to explain the unexpected better survival in overweight/mild obese patients.

Body composition for athletes is often better calculated using measures of body fat ( body fat calculator ), as determined by such techniques as skinfold measurements or underwater weighing and the limitations of manual measurement have also led to new, alternative methods to measure obesity, such as the body volume index. However, recent studies of American football linemen who undergo intensive weight training to increase their muscle mass show that they frequently suffer many of the same problems as people ordinarily considered obese, notably sleep apnea, some say that's not the best workout. A further limitation relates to loss of height through aging. In this situation, BMI will increase without any corresponding increase in weight.

Sit at a desk for long periods of time can cause muscular tension. You can prevent the buildup of stress in your muscles by taking a few minutes to stretch. Try these easy exercises when you need to re-energize, or throughout the day to keep your muscles relaxed:

Head Tilt. Put your right hand on your left shoulder. Tilt your ear right toward your right shoulder, but don't turn your head. Hold five seconds. Switch sides.
 

Neck Roll. Roll your head to the right, down to the front, then left. Do this slowly and smoothly, both directions.
 

Shoulder Circles. Make circles with your shouldersup, back, and down. Switch directions. Do at least five.

Side Stretch. Stretch your arms to the side, then clasp your hands overhead. Keep your head straight forward, but lean your upper body to the right side. You should feel this down your left side. Hold five seconds. Switch sides.
Back Release. Sit at the edge of your chair as tall as you can (be careful if it has wheels). Open your legs apart so your arms drop between them. Straighten your legs, so your heels are on the floor, but not your toes. Knees are relaxed and never locked. Bring chin to chest, and then roll down toward your feet, one vertebra at a time. You should feel this first in your neck, then upper back, middle back, and lower back. This should be done slowly, relaxing into each part of the back. Roll up just as slowly. This

Tips for being active
Give time every day for moderate aerobic physical activity like walking, swimming or biking. You should always stay within your physician's recommendations and your own comfort zone.

  DO...

Wear comfortable clothes and sneakers.
Start slowly. Gradually build up to at least 150 minutes of moderately vigorous physical activity per week (or whatever your doctor recommends). That's 30 minutes of activity, five or more times per week  If you can’t manage 30 minutes at a time, try two 15-minute sessions or three 10-minute sessions to meet your goal.
Exercise at the same time of day so it becomes a habit. For example, you might walk Monday through Friday before lunch or dinner.
If you aren’t on fluid restrictions, drink a cup of water before, during and after activity.
Ask family or friends to join you. You'll be more likely to keep exercising with company.
Track your activity on a printable log or online.
If you miss a day, plan a make-up day or add 10–15 minutes to your next session.
Vary your activity to keep your interest up. Walk one day, swim the next time, then go for a bike ride.
Join an exercise group, health club or community fitness facility. Many churches and senior centers offer exercise programs, too. (Get your doctor's permission first.)
Look for opportunities to be more active during the day. Park farther from your destination, walk the mall before shopping, choose a flight of stairs over an escalator, or take 10–15 minute walking breaks while watching TV or working.
Add strength and stretching moves to your routine, if your doctor allows them.
DON'T...

Get discouraged if you stop for awhile. Get started again gradually and work up to your old pace.
Perform isometric exercises that require holding your breath, bearing down or sudden bursts of energy. If you're taking part in a class or structured rehab program, ask the leader or therapist what isometric exercises are.
Get involved in competitive or contact sports such as football or soccer.
Engage in any activity that causes chest pain, shortness of breath, dizziness or lightheadedness. If you have any of these symptoms, stop what you're doing right away and call your healthcare provider.
Exercise right after meals, when it's very hot or humid, or when you just don't feel up to it.