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Get Fit with Math

Have a handle on basic algebra? Crunch some numbers to uncover some cool things about your caloric needs, body weight and workout intensity.

Don’t worry—we’re not going to rehash what you learned—or at least attempted to learn—in college calculus. But understanding some basic mathematical formulas will give you a clearer picture of how fit you are and help you set goals for where you’d like to be. Grab a calculator and get to work—no cheating.

Body Mass Index
Although it was once looked upon as the be-all and end-all of body weight calculations, there are arguments that BMI doesn’t take into account distribution of mass and therefore isn’t an accurate depiction of a person’s fitness. Still, BMI is the most widely used formula that organizations, like your health or life insurance provider, use to determine physical fitness.

BMI = (weight in pounds) / (height in inches)2 x 703

Does your BMI deem you normal, overweight or obese? Find out here.

Basal Metabolic Rate
Your BMR estimates the number of calories you would burn if you did nothing but sleep for 24 hours. It’s a great place to start when you’re calculating the number of calories you need to lose, maintain or gain weight. For men, the formula is:

BMR = 13.397(weight in kilograms) + 4.799(height in centimeters) - 5.677(age in years) + 88.362

Now, learn how to use your BMR to get your weight to where you want it to be. 

Target Heart Rate
Knowing your target heart rate is key to making effective use of your gym time. If you’re working out at too low of an intensity, you won’t see results. If you’re going too hard, you run the risk of injuring yourself—or growing to hate a particular workout.

There are a few steps to calculating your target heart rate. First, find your resting heart rate (RHR). As soon as you wake up, take your pulse for one minute while you’re still in bed. Do this for three days and take the average:

(Day 1) + (Day 2) + (Day 3) / 3 = RHR

Next, extimate your maximum heart rate (MHR) with this formula:

MHR = 220 - (your age)

Now, plug in the workout intensity you’re aiming for, which should be somewhere between 60% and 80%, depending on your goals. This formula will give you your target heart rate in beats per minute (BPM).

Target Heart Rate= [(MHR – RHR) × %Intensity] + RHR

To put this formula into action, strap on a heart rate monitor while you work out.

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