We took the standard human model (75kg), and made smaller and smaller models down to 100 grams. We also made the models bigger, up to 2,000kg, and challenged them to run as fast as they could.
Several fascinating things happened when we did this.
First, the 2,000kg model couldn’t move. Nor could the 1,000kg model. In fact, the largest model that could move was 900kg, suggesting an upper limit to the human form. Beyond this size we need to change shape in order to move.
We also found that the fastest model was not the biggest nor smallest. Instead, it was around 47kg, a similar weight to an average cheetah.
...Interestingly, many of our fastest long distance runners such as Eliud Kipchoge weigh around 50kg.
https://theconversation.com/not-too-big ... eed-241668