What is the average arm length

Mathematicians say the arm span to height ratio is one to one: your arm span goes once into your height. The femur bone is the only bone in your thigh. To measure its length, sit down and span a new piece of yarn over your thigh from the hip joint to the edge of your knee and cut the yarn there. Make an estimate. How many times would this piece of yarn go into the piece that is as long as you are tall?

Can you find a way to test your estimate? There are several ways to compare the length of the two pieces of yarn: You might cut several pieces of the length of your shorter string, lay them end to end next to your longer piece, and count how many you need. Another way is to fold the longer string into equal parts so the length of the folded string equals the length of the shorter string. The number of folds needed is exactly the number of times your shorter string goes into your longer string.

Did you see that the length of your femur bone goes about four times into your height? You can also say that if you divide your height in four equal pieces, you have the length of your femur bone, or the length of your femur bone is one fourth of your height. Mathematicians call this a one to four ratio. How many times would the length of your head fit into your height?

Maybe four, six or eight times? To test six times, fold the yarn with length equaling your height into six equal pieces.

Have your helper place a book flat on your head and hang the folded string from the side of the book. If the other end of the string is about level with your chin, your height would be about six times the length of your head, or your head to body ratio would be one to six. Which number of folds fits best for you? There are many more bodily ratios you can explore: the circumference of your head compared with your height, or the length ratios of your forearm and foot or thumb and hand.

Extra: You have explored some ratios in your body and might wonder if these hold for other people as well. Do you think they hold for most people of your age?

What about adults or babies? Do you think these ratios hold for them or would some be different? Make a hypothesis, find some volunteers, measure and compare. Was your hypothesis correct? Extra : This activity uses pieces of yarn to compare lengths.

You can also measure your height, arm span, femur bone, etcetera with measuring tape, round the values and write the ratios as fractions. Can you find a way to simplify these fractions? Extra : Draw some stick figures on a sheet of paper. Can you apply some of the bodily ratios you explored like the arm span to height or the head to body ratio to the figures?

Which ones look most realistic to you? Extra : Ratios are all around us. Can you find other places where ratios play an important role?

To get you started, think about a recipe and the ratio of the quantity of one ingredient to another. For avid bikers, can you find the ratios that correspond to the different gears on a bike? Build a Cooler. Holes That Do Not Leak! Lift a Large Load Using Liquids.

Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options. Continue reading with a Scientific American subscription. Subscribe Now You may cancel at any time. With that said, from what you described, you have incredible genetics. Therefore, if you decided to do a bodybuilding-style training routine as a beginner, your first goal should be around 14 inches.

FYI the average male arm size is about So if you add 2 inches to that so around 16 in they should be considered big. How impressive are 13 inch forearms? The research is clear. If you have 13 inch forearms, then your size is well above average, which is right around 9.

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