Alex Hutchinson has the interesting details in Outside. The test was only for one athlete and the guy who did the study said it statistically should be considered a dead heat.
Alex Hutchinson wrote:
[Canadian marathon record holder Malindi Elmore] brought in a pair of Saucony Endorphin Pros and a pair of Vaporfly Next%, which at the time was the newest Nike model. She ran a series of short stages on the treadmill, starting at 14 km/hr (6:54 per mile, on pace for a 3:00 marathon) and progressing up to 17.6 km/hr (~5:30 per mile, 2:24 marathon pace), while breathing through a mask to measure her oxygen consumption. On the first day, she did the entire test sequence in the Nikes then repeated it in the Sauconys; on the second day, she did it the other way around to ensure the results weren’t skewed by fatigue.
McCasey knew about the testing plan. “Of course, there are natural nerves when Saucony’s lead innovation story, the Endorphin Pro, would be stacked up against our competitors by a third party,” she admits. Although no one has released any data publicly, the Next% is rumored to be another percent or two better than the original Vaporfly 4%—a formidable benchmark for the Endorphin Pro. But the results, it turned out, were a wash.
Here’s what the data looked like at 2:24 marathon pace, which is what’s most relevant for Elmore’s race goals, averaged over both days of testing:
You can see that the values are nearly the same: 181.4 ml of oxygen per kilogram per kilometer in the Vaporflys, and 180.5 ml/kg/km in the Endorphins. A lower number is better, because it means you’re burning less energy to sustain the same pace. But in this case, the 0.5 percent difference is much smaller than the “smallest worthwhile change” (SWC), which is a statistical measure of how much running economy values tend to vary between different runners. It’s also smaller than the “typical error,” which is a statistical measure of how much running economy values tend to vary when you test the same runner under the same conditions over and over. So the Endorphins are a tiny bit better numerically, but statistically it’s a dead heat.
In my mind, I find this to be interesting but am not going to accept it as fact considering it's so limited in size and has quotes from PR people at Saucony. I think it's a joke that a larger study hasn't been done. I've talked to Geoff Burns about doing one ourselves.
We need to know how the shoes from various companies stack up and we need to see how much the response varies person to person. What if we learn that one athlete is way better in only a certain brand's shoes?