Body weight and running performance

How does body weight affect performance?

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

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.

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.

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.

Speed gain from weight (fat) loss
Fat loss 5k 10k HM M
2lb 12.4 secs 25 secs 52 secs 1:45
5lb 31 secs 1:02 2:11 4:22
10lb 1:02 2:04 4:22 8:44
20lb 2:04 4:08 8:44 17:28

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.

Improve your body composition and get a personalised running plan with our sportnaturally plans.

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