Human body weight

Key takeaways

Human body weight belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Human body weight to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Human body weight from memory before moving on to harder problems.

Reference excerpt

Human body weight is a person's mass or weight. Strictly speaking, body weight is the measurement of mass without items located on the person. Practically though, body weight may be measured with clothes on, but without shoes or heavy accessories such as mobile phones and wallets, and using manual or digital weighing scales. Excess or reduced body weight is regarded as an indicator of determining a person's health, with body volume measurement providing an extra dimension by calculating the distribution of body weight.

Estimation in children

There are a number of methods to estimate weight in children for circumstances (such as emergencies) when actual weight cannot be measured. Most involve a parent or health care provider guessing the child's weight through weight-estimation formulas. These formulas base their findings on the child's age and tape-based systems of weight estimation. Of the many formulas that have been used for estimating body weight, some include the Advanced Pediatric Life Support formula, the Leffler formula, and Theron formula. There are also several types of tape-based systems for estimating children's weight, with the best-known being the Broselow tape. The Broselow tape is based on length with weight read from the appropriate color area. Newer systems, such as the PAWPER tape, make use of a simple two-step process to estimate weight: the length-based weight estimation is modified according to the child's body habitus to increase the accuracy of the final weight prediction. The Leffler formula is used for children 0–10 years of age. In those less than a year old, it is

m = 1 2 a m + 4 {\displaystyle m={\tfrac {1}{2}}a_{m}+4}

and for those 1–10 years old, it is

m = 2 a y + 10 {\displaystyle m=2a_{y}+10}

where m is the number of kilograms the child weighs and am and ay respectively are the number of months or years old the child is. The Theron formula is

m = e 0.175571 a y + 2.197099 {\displaystyle m=e^{0.175571a_{y}+2.197099}}

where m and ay are as above.

Fluctuation Body weight varies in small amounts throughout the day, as the amount of water in the body is not constant. It changes due to activities such as drinking, urinating, or exercise. Professional sports participants may deliberately dehydrate themselves to enter a lower weight class, a practice known as weight cutting.

Ideal body weight Ideal body weight (IBW) was initially introduced by Ben J. Devine in 1974 to allow estimation of drug clearances in obese patients; researchers have since shown that the metabolism of certain drugs relates more to IBW than total body weight. The term was based on the use of insurance data that demonstrated the relative mortality for males and females according to different height-weight combinations. The most common estimation of IBW is by the Devine formula; other models exist and have been noted to give similar results. Other methods used in estimating the ideal body weight are body mass index and the Hamwi method. The IBW is not the perfect fat measurement, as it does not show the fat or muscle percentage in one's body. For example, athletes' results may show that they are overweight when they are actually very fit and healthy. Machines like the dual-energy X-ray absorptiometry can accurately measure the percentage and weight of fat, muscle, and bone in a body.

Devine formula The Devine formula for calculating ideal body weight in adults is as follows:

Male ideal body weight = 50 kilograms (110 lb) + 0.9 kilograms (2.0 lb) × (height (cm) − 152) Female ideal body weight = 45.5 kilograms (100 lb) + 0.9 kilograms (2.0 lb) × (height (cm) − 152)

Hamwi method The Hamwi method is used to calculate the ideal body weight of the general adult:

Male ideal body weight = 48 kilograms (106 lb) + 1.1 kilograms (2.4 lb) × (height (cm) − 152) Female ideal body weight = 45.4 kilograms (100 lb) + 0.9 kilograms (2.0 lb) × (height (cm) − 152)

Usage

Sports Many disciplines in weightlifting or combat sports separate competitors into weight classes.

Medicine Ideal body weight, specifically the Devine formula, is used clinically for multiple reasons, most commonly in estimating renal function in drug dosing, and predicting pharmacokinetics in morbidly obese patients.

Average weight around the world

By region Data from 2005:

By country

Global statistics Researchers at the London School of Hygiene and Tropical Medicine published a study of average weights of adult humans in the journal BMC Public Health and at the United Nations conference Rio+20.

Worked examples

Example 1 — a first encounter with Human body weight

Start with the simplest possible case. Write down what Human body weight claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Human body weight before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Human body weight ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Human body weight

In research: Human body weight appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Human body weight in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Human body weight is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anthropometry, Auxology, Human body weight, so understanding it makes those chapters shorter.
In everyday life: Look for Human body weight outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Human body weight in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Human body weight means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Human body weight out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Human body weight in simple terms?

Human body weight is a person's mass or weight. Strictly speaking, body weight is the measurement of mass without items located on the person.

Why does Human body weight matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Human body weight?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Human body weight.