How Much Does Weight Actually Matter In Running?

How Body Weight Affects Running

The video argues that body weight affects running performance, but the number on the scale is only one factor.

It opens with the common estimate that losing a pound might make a runner about one second faster per mile. This estimate is linked to a 1978 study, which found that each extra pound could slow a runner’s pace by about 1.4 seconds per mile. However, the presenter cautions that getting lighter does not automatically make someone faster.

Where Weight Is Carried Matters

A 2007 study is cited for the finding that supporting body weight can use up to 74% of the energy involved in running. The location of that weight also matters: weight in the legs can be more costly than the same amount in the trunk because it takes more energy to swing and stabilize weight farther from the body’s center of mass.

The presenter says this is why reducing the weight of shoes and other gear can be especially useful.

Fitness Can Matter More Than Weight

The video challenges the idea that lighter runners always perform better. A study of ultra-runners reportedly found that heavier runners could match or sometimes outperform lighter competitors, often because their greater overall fitness offset the disadvantage of carrying more weight.

The presenter also shares an example from his professional triathlon career: a 95 kg training partner could run a 5K in 15 minutes and 30 seconds. His advice is to focus on improving performance rather than devoting all your effort to weight loss.

Avoid Under-Fueling

The presenter warns that training hard while eating too little can cause relative energy deficiency in sport (RED-S). Inadequate energy intake can weaken the immune system, harm recovery, and reduce performance.

He recommends judging progress by whether you are running faster or farther, and attempting weight loss when training demands are lighter.

Strength Training and Running Economy

The video presents strength as another route to faster running. It compares the body to a phone: weight is like the phone’s size, while muscle power is like its processor.

According to the presenter, scientific reviews have found that strength training can improve running economy by 2–4% without requiring weight loss or gain. He recommends adding strength work or hill sprints.

Presenter and Sources

Presenter: Nicklas Rossner

Sources mentioned:

• A 1978 study on body weight and running pace
• 2007 research on the energy cost of supporting body weight
• A study of ultra-runners
• Scientific reviews on strength training and running economy