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What Is a Good BMI for Running a 5K?

author image Julia Whidden
Julia Whidden is a registered, licensed dietitian in the state of Ohio. She obtained her B.S. in nutrition and dietetics at Seton Hill University in Pennsylvania, while also acting as captain of the university's NCAA track-and-field team. Whidden now works for the J.M. Smucker Company as a nutrition analyst.
What Is a Good BMI for Running a 5K?
Improve your race time by losing weight slowly.

Running five kilometers can be a challenging and rewarding experience at the same time. Whether you run competitively or just for fun, extra body weight may be holding you back from achieving your goal time. Body Mass Index, or BMI, can give you a starting place to achieve your optimal weight. But finding your best performance weight may require other methods of assessing body composition.

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Defining BMI

BMI is a calculated number determined by dividing your weight in kilograms by your height in meters squared. The Centers for Disease Control and Prevention states that it is a fairly accurate indicator of body fat for the general population. BMI measurement less than 18.5 is underweight; 18.5 to 24.9 is normal weight; 25.0 to 29.9 is overweight; and 30.0 or more is obese. Many highly trained athletes have a higher percentage of lean body mass than nonathletes, and BMI may not be an accurate way of assessing their body composition. Because muscle is more dense than fat, a high BMI for an athlete is not uncommon.

Mass versus Weight

Matt Fitzgerald, author of the book "Racing Weight: How to Get Lean for Peak Performance" explains that body fat percentage is a more accurate measure of optimal racing weight, because it takes lean muscle mass into consideration, rather than just body weight. Because your lean muscle contributes to force production, it enhances performance rather than slowing you down. Fitzgerald recommends obtaining a body fat percentage within the 80th percentile for your age and gender. Consult a trained fitness professional to get an accurate assessment of your body fat percentage.

Tweak to Peak

In addition to targeting a specific body fat percentage, Fitzgerald recommends experimenting with your weight to achieve optimal performance. Pay attention to how you feel before, during and after running. Too low body weight may hinder rather than enhance your performance. Losing weight quickly may result in loss of lean muscle mass that is critical for optimal performance. Fitzgerald notes that achieving optimal weight is a process of training and eating right that takes place over an extended period of time.

How to Safely Lose Weight

If you are a competitive athlete, losing weight during the off-season will be most beneficial. However, when you are in season, be sure to lose weight safely and slowly. Making sure your body has enough nutrients is essential to a better running time. Without the right amounts of carbohydrates, proteins, fats, vitamins and minerals, your body will not be able to keep up with your training. Try cutting back on big portions. Include more fruits, vegetables and whole grains. The fiber from the fruits, vegetables and whole grains will help you feel full longer.

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