Running is still one of the most popular ways to get exercise and running faster gives instant gratification. Finding out how to calculate your perfect running weight can bring those personal best times down dramatically.
Many studies, including one in Medicine & Science in Sports & Exercise, show that running with even a little extra weight can cause a significant drop in performance. If you’re an intermediate or advanced runner trying to find an extra few seconds, getting to your perfect weight can cause a positive knock-on effect.
Peak body weight can improve VO2 max, helping to increase oxygen intake. Even at the most basic level, running with the right body weight will feel better than if you are either carrying too much (increasing load on your muscles and joints) or too little (fat is essential to runners, and a lack of it leads to muscle catabolism making you weaker and slower).
So, get out your calculators or spreadsheets and get ready for some maths. It’s time to find your perfect running weight.
First, you’ll need to know your body fat percentage, or BF%. There are several ways to achieve this.
The most accurate would be to find a BodPod and book a session. Failing that, a full body composition mat (sometimes available in gyms) or a series of caliper tests will get you close to a correct figure. Body fat composition scales, such as the Fitbit Aria, will produce good results but they won’t be as accurate as a full body mat or a BodPod session (which is the most accurate by far).
If you use calipers, make sure you use the Jackson/Pollock 7-point test and always have the same person conduct the tests. You can calculate the results using Linear Software‘s online calculator, and you should take an average number from three or four tests over the course of a week to get the best result.
Once you have your BF%, convert it into a decimal. For example, 18% body fat = 0.18.
Now, calculate your actual body fat in pounds.
Current weight (pounds) x decimal BF% = body fat (pounds)
For example, 162 x 0.18 = 29.16.
Now that you have your body fat weight in pounds, you can calculate your lean mass.
Current weight (pounds) – body fat (pounds) = lean mass.
For example, 162 – 29.16 = 132.84.
Target Lean Mass
Now, this is where we can’t offer a ‘one size fits all’ metric. Different body types will require different levels of body fat, but we can use a short range of targets based on whether you are male or female because this article is specifically about running, and we’re expecting you to be of intermediate or advanced level in the first place.
If you are a male runner, your target should be to reach 12% to 15% body fat. For females, this should be 18% to 22%. While both men and women can have lower body fat percentages, runners need to have fat stores available so keeping within these ranges is recommended.
With your target body fat percentage chosen, turn it into a decimal again. Then calculate as follows:
1 – target decimal BF% = target lean mass.
For example, 1 – 0.14 = 0.86
Now that we have the target lean mass, we can work out our target weight.
Lean body mass divided by target lean mass = target weight (pounds).
For example, 132.84 / 0.86 = 154.46 pounds.
In our examples, a 162 pound male with 18% body fat that wants to hit a running-friendly 14% body fat will weigh 154 pounds in a perfect world, giving that person a goal of losing eight pounds of fat. How do you lose that weight and ensure it is body fat that is being sacrificed and not muscle weight? That’s for another article…
For now, and for those runners out there that consider themselves intermediate or advanced, this guide will help you determine a better running weight to assist with those personal best times.