Fitness Fun Facts

I was born in 1983 and will be 26 years old very soon! I weigh 145 lb. I am 5'7".

This information is very basic and very static (except for the ten pound weight gain since I started med school.) It is a part of who I am -- it's on my driver's license after all. It is a part of the Vital Signs, measurements that doctors utilize to determine your health!

Using myself as an example, I will go through a few calculations quickly that you might find interesting.

Body Mass Index (BMI):
Everyone and his mother knows what BMI is. It basically categorizes people as ok (BMI 18.5-25), overweight (>25), underweight(<18.5), obese (>30) or morbidly obese (>35).
You calculate it by taking your weight(in kg) and divide your height(in m) to the second power. Or use can use an online calculator or chart. Be warned though, that it just measures weight - it makes no distinction between fat and muscle (a confounding factor that tells us Arnold Schwartznegger is obese.)

Example: I am 5'7"->170cm->1.7m and 145lb -> 65.8kg.
Wt(kg) / Ht(m)^2 = BMI
65.8kg/1.70^2 = 22.77
My BMI is in between 18.5-25, so I am of normal weight for my height.

Ideal body weight (IBW):
This is something that differs for men and women.
in men, the IBW is 106 lb, plus 6 lb for every inch above 5'.
in women, the IBW is 100lb, plus 5 bl for every inch above 5'. Tough break!

Example: I am 5'7", therefore 7" above 5'.
106(lb) + 6(lb)*(7) = 148 lb

I notice that this does not correlate with other results I've found online... but this is the most straight-forward formula I've found (in an NMS Family Medicine text)

Image via Wikipedia

Heart Rate target with exercise
Now for some of the fun stuff!
Your maximum heart rate is 220-age in beats/second. For moderate exercise, it should be 70% of that, or 0.7(220-age.)

Example: my age is 26.
0.7(220-26) = 135.8

You can find your pulse on your wrist (radial pulse) by making a fist and curling your hand to find the pit formed by your flexor tendons. Place your index and middle finger in that pit at the base of your thumb after relaxing your hand. To find your pulse in your neck (carotid pulse), poke the back corner of your jaw and slip your two fingers underneath the mandibular angle up against your neck. (The guy in the wikipedia picture has his fingers slightly malaligned for a perfect pulse... if he slid them down further he'd get it right on the pads of his fingers..) Count the beats for a minute (or alternatively, for 15 seconds and multiply by 4.)

Caloric expenditure for walking one mile:
How many calories (technically it is kilocal) do you burn walking one mile?
Take two thirds of your weight(in lb)! Simple... but scary too.

Example: I weigh 145#.
2/3(145) = 96.67 kcal

That means if I eat one of those little 100cal snack packs, I need to walk a mile to burn it off! If I drink an extra can of coke, I need to walk a mile and a half! No wonder I've gained weight. It also can be put into the context of cutting out one cookie every day. Over the course of a year, you would prevent an average of a ten pound weight gain assuming everything else was equal. (per personal communication with a physician who co-authored the DASH diet.)

Energy requirements for a typical day:
The kilocalories we need is about 10*IBW per day.

Example: my IBW(see above is 148).
10*148 = 1480
Assuming the average American male is ~5'9"...
10* (106+6*9) = 1600

That must be where the generic 1600 kcal ADA diet recommendation comes from.

Weight loss:
Mathematically, this requires a caloric deficit. That means more calories out (burned) than calories in (eaten.) There's a lot of different diet plans floating out there online on how to lose weight. I'm not going to go into that in this post. A very aggressive weight loss plan to lose a pound per week would be a 3500 cal/wk or 500 cal/day deficit.

That's walking five miles a day! A word of caution though... the goal is to lose fat, not water and muscle! Any faster and you risk dehydration, lactic acidosis buildup and muscle breakdown from starvation.

A more reasonable goal is perhaps simply walking a mile or two three to five days out of the week. A pound of weight loss every month may be seen with this. Coupled with diet changes... you'd be set to start living healthier and wiser! I know I'll try to keep these things in mind for myself as I strive to rebuild some of my lost muscle in lieu of brain power over the past three years of med school. ;)