Another way to check your weight is to calculate your Body Mass Index or BMI. Your BMI is a ratio or comparison of your height and weight expressed in a number. To find out your BMI you need to divide your weight (measured in kg) by your height (measured in metres) squared.

The accepted definitions of weight categories by BMI are: · Underweight – less than 20 · Healthy weight – between 20 – 25 · Overweight – between 25 – 30 · Obese - greater than 30 These BMI values only apply to adults aged 18 years and over and are based on studies of Caucasian populations. Therefore, they are not applicable to children and adolescents and they may not be appropriate for people of other cultural backgrounds.

The BMI does not take into account ratio of body fat to muscle. Very fit, muscular people may register with a higher BMI but not need to lose weight.

A more reliable system to estimate how overweight you are and which takes into account your muscle mass is amount of body fat as a percentage of total body weight. You can estimate your body fat and obtain a report on your healthy weight at website listed in authro's resource box.

Training Weight training uses principle of adaptation. By lifting a heavy weight, your body needs to expend some calories by burning blood-sugar and also uses up some nutrients. But that's trivial. More importantly, main effect of weight training is that in days afterward, muscle will slightly increase in size and strength. Why does this happen? Adaptation. Because message you're giving your worker muscle cells is that their job is to lift a massive weight, and your survival may depend on it. Your muscle worker thinks: "I could just barely do that today, so tomorrow I'll need to be a bit bigger, just in case it happens again." The muscle is adapting to stimulus of a heavy load by making it a little easier for you to lift that load in future.

Survive! To your body, everything is a matter of survival, and most important element that your cells try to maintain is your energy. If you don't have energy to chase down your food, you will starve, and if you don't have energy to run away from a predator, you will be their food. If you burn though energy too quickly, there won't be enough left over to live on. That's why your body loves to keep fat: it's good for survival if food runs out.

The key to understanding adaptation is to think of yourself living in African savanna, and what your activities would mean if they were applied only to your survival. When you run, your cells think, "We must be running to catch food, or to escape death!" That's all that cells know: survival.

To bodybuilder, question becomes, "Will lifting a heavy weight make me stronger?" The answer is No! The immediate effect is that it will make you weaker. If you lift 100 lbs 10 times, does that mean that you can then lift 120 lbs right away? No, you're weaker and tired from your previous work. But your body will think that it needs to lift 100 lbs 10 times in order to survive, so it will adapt to make that a little easier for you next time. Taking a week off and allowing time for your muscle to grow a little bit will mean that you are stronger. So, next week you lift 120 lbs, and your body needs to adapt AGAIN, thinking that you now need to lift 120 lbs to survive. This makes you stronger week by week. "Will lifting a light weight 50 times make me stronger?" No! Your muscle will be exhausted, but you're asking for it to be able to last longer, not grow stronger. How will your body last longer? By adapting your energy stores (fat) to release more slowly and gradually. This is great for your endurance, but BAD NEWS if you want to look "ripped" with little body fat.

But adaptation does not only apply in this case. Your body adapts to everything. Everything you do and eat. So, you have to ask yourself, "Am I sending my cells right message in things I do and food I eat?"

Look for sequel to this article, Adaptation II, for tons of examples and practical advice based on principle of Adaptation.