[polotics]

Lots of missing variables in the equation: how much do you carry, how much of your body weight is useful muscle versus the rest, etc... I suspect the announced most-efficient run speed is for the most efficient (light) runner.

[AmericanChopper]

I wouldn’t be surprised if it was quite generalizable. The lost efficiency has to be from the increased vertical travel required from running (followed by the additional stabilization required), I wouldn’t be surprised if the most efficient ratio of vertical to forward travel was very similar for a wide range of weights.

I’d be more interested in how they collected the data. A skilled and fit runner will run a lot more efficiently than a less skilled and less fit runner, and you’d also expect a skilled/fit runner to run faster than a less skilled/fit runner. So depending on how they collected the data, that could be a big confounder.