• Isaac J. Wedig MS, CSCS

How to use Bodyweight Measures Effectively

Bodyweight measures can be a very useful tool in tracking your progress. They're convenient, cheap, and very helpful in gauging whether or not your energy balance is in an appropriate place. If you're losing weight consistently over time, its a pretty good indication that you're in a calorie deficit and achieving fat loss. Likewise, if you're performing resistance training and your bodyweight is increasing over time, its a good indication that you may be building some muscle.

However, their are also some inherent limitations to bodyweight measures when taken alone. It’s very important to understand these limitations, analyze your bodyweight data appropriately, and be sure to utilize other methods to track your progress in addition. Often times, its not simply changes in bodyweight that we are actually seeking, its changes in body composition, the relative amounts of fat mass to fat-free mass. The problem with bodyweight is that it doesn't directly measure this. It can be misleading because it may not be measuring what you think it is.

Before describing how to use bodyweight most effectively, it’s important to understand what variables can affect it. This will help you in properly interpreting your bodyweight data.

Factors that Effect Bodyweight

Bodyweight can fluctuate by up to 1-2% on a daily basis, which can equate to a daily change as high as 5lbs in some individuals. The small fluctuations that occur from day-to-day are not likely representative of body compositional changes, or in other words, they are not due to changes in fat or muscle content. Typically, these fluctuations are due to changes in hydration status, changes in the amount of stored carbohydrates, or alterations in food bulk and the amount of food that is consumed.

Listed below, there are several different variables, other than changes in body fat and muscle, that can affect bodyweight on a short-term time frame.

1) Sodium intake- consuming an abnormally large amount of sodium, beyond what your body is normally accustomed to, can cause water retention and lead to an increase in scale weight. Likewise, a sudden and drastic drop in sodium intake can decrease scale weight.

2) Carbohydrate intake- carbohydrates are stored both in the liver and to an even greater extent, within skeletal muscle. Consuming more carbohydrates than usual can lead to an increase in these stores. Also, for every gram of carbohydrate that you store, it also pulls about 3 grams of water with it. The increase in carbohydrate and water in turn increases your bodyweight. Likewise, if you reduce carbohydrate intake, increase your physical activity level, or a do a combination of both, carb stores will drop and so will bodyweight.

3) Stress- both psychological stress as well as a lack of sleep can both alter you’re eating habits as well as affect your body’s hormonal status. Both of which can lead to water retention and increased scale weight. Infection, as well as muscle damage occurring in response to training, also forms of stress, can lead to inflammation and fluid retention as well. Going from a high stress state to a lower stress state, or from poor sleep to good sleep, can cause a decrease in bodyweight.

4) Menstruation- hormonal shifts during certain phases of the menstrual cycle can cause changes in fluid retention. Men, this is not a problem for you.

5) Alcohol- alcohol is a diuretic and can cause a loss of body fluids and dehydration, thus decreasing bodyweight, as long as calories are controlled. Alcohol consumption also tends to increase hunger and promotes the consumption of excess calories, which in turn may potentially increase weight. A night of heavy drinking will most likely exert some effect on bodyweight.

6) Food Bulk and Digestion rate- eating higher volume, higher fiber foods, and more ‘food bulk’ than usual can lead to weight increases simply as a byproduct of excess food sitting within your digestive system. Changes in your digestion rate or a deviation from the regularity of your bowel movements may affect bodyweight as well. Less regular movements or constipation can increase bodyweight, while diarrhea or more frequent bowel movements can decrease weight.

7) Drug use- antidepressants, anti-inflammatories, and steroids, including birth control, and a number of other prescription drugs can alter fluid balance as well.

As you can see, bodyweight is affected by much more than just fat and muscle amounts. When it comes to your physique goals, if all your measuring with bodyweight is fluctuations in water and food bulk, then what good is it?

A good quality measure has to have validity. In other words, it has to measure what you’re actually trying to measure. For physique goals, the primary thing that you’re interested in measuring is body composition, the relative amounts of body fat and muscle mass, not hydration status. Bodyweight alone is not a very valid measure when it comes to assessing body composition or physique goals. It can be very misleading, frustrating, and defeating at times. However, when used and interpereted appropriately, it still has merit and can be very useful in guiding you in the right direction.

How to use Bodyweight Measures Effectively

If you wish to use bodyweight as a measure of progress, which I do recommend, you must be sure to do these three things; 1) take consistent measures, 2) compare weekly averages, and 3) use it in conjunction with other measures.

1) Take consistent measures

Consistency of your weigh-ins is very important. This means taking your weight at the same time of day, in the same clothes, and in the same fed/hydration state each time you weigh-in. The best way to ensure consistent weigh-ins is to record your bodyweight every morning upon waking, after using the bathroom, before consuming any food or beverage, and preferably in the nude. Try to use a digital weight scale as they are more accurate and consistent than a spring mechanism.

2) Compare weekly averages

You aren’t interested in measuring and comparing day-to-day changes in bodyweight that come from fluctuations in hydration status, carbohydrate intake, or food bulk. By taking weekly averages, you can smooth out the small variations that occur on a daily basis, highlighting only average changes that occur on a week-to-week basis, which are more likely to be representative of changes in body tissue (fat and muscle) rather than other factors.

Try to collect good consistent bodyweights as many days of the week as you can. The more days that you collect, the better that your averages will represent the week. In order to use bodyweight as a decent proxy of energy balance and tissue change, compare your averages from week-to-week. If your average bodyweight trends appear to match up to your desired goal, then you’re on the right track. If fat loss is your goal, weekly averages should be declining. If muscle gain is your goal, then weekly averages should be increasing. If this isn’t the case, your training and nutrition may need some tweaking and your energy balance probably isn’t where it should be.

3) Use in conjunction with other measures

When measuring your progress on a diet and exercise program, it’s important not to put all your eggs in one basket. Generally, the more measures that you use, the better. It’s a bad idea to relying exclusively upon one measure to guide your journey, especially when it comes to physique goals.

With a physique goal, we’re not just interested in weight, we want to measure relative changes in body fat and muscle. The idea is to reduce fat and increase muscle. Therefore, in addition to bodyweight, we need to utilize methods that can help to specifically detect changes in fat and muscle amounts.

These may include physique pictures, body circumference measures, skinfolds, body composition tests, and gym performance. Although all of these measures carry their own inherent limitations, when taken collectively together, they provide a much more comprehensive report of your progress.

These alternative measures can help to detect changes in body composition that might have otherwise gone unnoticed by monitoring bodyweight alone. For example, say that your bodyweight remained unchanged yet your waist circumference and belly fat skinfold measures deceased. You clearly had losses in body fat around your midsection but they were masked by increases in bodyweight that might have come from extra water retention. Had you measured bodyweight alone, you would have missed your progress, gotten frustrated, and possibly abandoned ship on your diet.

For most individuals I recommend using bodyweight in combination with physique pictures, body circumferences, and perhaps even skinfolds. These are the most convenient, inexpensive, and practical measures to use. As a note on skinfolds, the best way to utilize them is to compare relative skinfold thicknesses from specific sites over time, rather than using them to calculate and compare relative body fat percentages. If the skinfold amount is decreasing at a particular site over time, then it’s safe to say your losing fat at that spot. Having them done by a trained and experienced professional is a good idea as well.

An additional measure, which can be great for tracking changes in muscle mass, is gym performance. If you are able to perform more repetitions with a given weight, across multiple sets, that’s a decent indication that muscle growth has occurred. This is even more accurate with single-joint, isolated exercises such as bicep curls, leg extensions, and chest flyes, particularly when using machines.

If performance has dropped over time, it may indicate muscle losses. Again, as with the other measures, there are limitations and certain assumptions with correlating muscle mass to performance, however, it serves as one more tool and some additional data to consider. The more you measure, the more you can manipulate. If you don’t track your progress at all, then you’re left in the dark and have no way to tell if you’re on course towards your goal.


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