Body weight and running performance

How does body weight affect performance?

Well, it’s a bit of a flawed question!

Approx read time: 2 mins
running-fat percentage-exercise-marathon training

Body composition and running

It depends whether the weight comes from fat or muscle. Carrying extra fat is like strapping a dead and useless load to yourself, your body has to work harder to lug that load around your run or race. It’s simple physics that a light machine with a strong engine travels faster. The engine being your muscles.

Your fat percentage will have a bearing on your running 

Yes we can all cite people who are overweight and come storming past us in races but look at the front pack, they’re whippets. Look at the back of the pack and the opposite is often the case. I see the proof a lot in my clients; they lose fat and they get faster, even if that wasn’t the main driver and even if their training stays the same. Albeit losing fat will help them to train faster too.

Fat percentage is key, weight itself doesn’t tell you about body composition. Compare Usain Bolt’s body against Mo Farah’s. Usain will be lots heavier due to his muscle poundage, which gives him power; Mo will be very light, in order to aid endurance, but they will share a similar fat percentage.

Running speed gain from weight (fat) loss

Amby Burfoot, winner of the Boston Marathon and leading running author, came up with the table below which illustrates the speed gain from losing pounds of fat.

Fat loss5k10kHMM
2lb12.4 secs25 secs52 secs1:45
5lb31 secs1:022:114:22

(5k = 5 kilometers – 3.1 miles, 10k = 10 kilometers – 6.2 miles, HM = Half Marathon – 13 miles, M = Marathon – 26 miles)

If you’re trying to lose fat as a runner it’s important that you do it correctly so you don’t compromise your nutrition. The less food you eat, the more important it is to pay attention to nutrients, though of course that is always important! Take it slowly; fast weight loss = muscle loss, steady weight loss = fat loss.

Improve your body composition and get a personalised Sports Nutrition.

Personalised Sports Nutrition

Get your nutrition fully dialled in with our Personalised Sports Nutrition plan for improved performance, sport-appropriate body composition, robustness and fantastic health.

Table of Contents

FREE consultation
Schedule a free 15 minute consultation with Sally, Nuush’s founder and lead nutrition advisor, to talk through your nutrition, health or performance.
Nutrition Plans
Join one of our Mediterranean diet plans and experience the health benefits of a balanced and nutritious lifestyle.

Share this post

Thank you for reading this article. Please note that while we share a lot of awesome information and research you should be aware our articles are strictly for informational purposes and do not constitute medical advice intended to diagnose, cure, treat or prevent any disease.

Cover photo by epicstockmedia, from