Promising Heart Rate Metrics for Airia 1.5 in First Pilot Study
Long before Airia was founded I was approached by our inventor, Svante Bergren, to test some odd-looking prototype running shoes. They were based on an Asics Gel-Igs. I was also given the same Asics Gel-Igs without modifications as a reference. I had gotten out of my running habit, and was in between two good places in my life.
I brought the shoes to the Las Vegas Hockey Fair. I guess I figured I would need exercise with all the beers and steaks I would probably consume. The first morning I went down to do a test run with the Reference shoe. It all went well for the first 15 minutes, but then it started to hurt. I had set the speed to above my fitness level on the treadmill. I broke through the pain, but still ended the run 5 minutes earlier than planned. The following evening went as I suspected, with beers and steaks.
The next morning I was afraid to enter the gym. Not only was I supposed to run at a speed more than my limit, but I also had small hangover. Too much food in my stomach and some ugly prototype running shoes which barely held together was not a good combination. That was when I was sold on the technology in Airia running shoes. I managed to complete the planned exercise, and it felt like I could go on forever. Back in Sweden I left the Hockey company to work with Airia full time.
I did a lot of those fixed-speed tests in the beginning of the development of the Airia One running shoe. I often did the same time and speed in different shoes and compared the end heart rate. Eventually we felt the heart rate test was not the best predictor for race finish times. Since then we have mainly used full speed 5k test runs [link to white paper] on an indoor track to compare shoes. We forgot about the treadmill heart rate tests.
Recently we brainstormed ways for anyone to try comparative shoe tests from a performance perspective. The main thing we wanted to accomplish was to demonstrate the difference you can get from our shoes. But the more we thought of it, the more it made sense to help bring forth some kind of shoe test that anybody can do, for any shoe. In the end, our old heart rate test came up as a good candidate. Since I was the only test subject, the question arose: Would it hold for more participants?
Design of pilot study
• 2 shoe models tested, Test shoe (Airia 1.5) vs Reference shoe of comparable weight.
• 4 Runs, 2 in each pair of shoes.
• Test run on treadmill.
• Fixed-speed set to test subject’s 10K race pace (or an end of test HR of 80% of MAX HR)
• Test time 25 or 30 minutes, same for all 4 runs but different for different test subjects.
• Heart rate monitor to collect data.
• At least one day rest time between test runs.
The shoes we decided to test were Airia 1.5 vs a reference shoe of comparable weight. It would have been better if every test runner would have used the same reference shoe. Still the test tells a story of the test shoe compared to these other shoe models. Each runner then made four test runs, two times with the test shoe and two times with the reference shoe. The order in which the test shoes were used was randomized.
We did the test on a treadmill to get constant speed. The treadmill was not calibrated but we used the same treadmill for all four tests. That is a good way to get consistent data even though the speed won’t be exactly what you enter on the treadmill panel. Most gym-quality treadmills are pretty good at giving the right speed. If you use a home treadmill it may be more difficult to get consistent speed.
We used both Garmin and Polar Heart rate monitors. Polar may have an edge in reliability compared to Garmin, but we don’t favor any over the other. You can probably use any heart rate monitor. You just can’t measure heart rate at the end of the run by hand. The heart rate will lower too fast.
In this, our initial pilot, we only had 5 test runners. This was too few to draw any strong conclusions. But even so, the results are interesting enough. We can clearly see a difference between the reference shoes and the test shoe.
To compare the data, we first took the average HR per each 2 minute period for both runs in one shoe. This compensates a bit for reading error on the heart rate monitor and events that can happen during the run. It also gives us one curve for one shoe and one runner. We can then plot a graph using this data to compare the two shoes on an individual basis. In all five cases it was a clear and noticeable difference between the test shoe and the reference shoe. Four runners had better results with the test shoe and one runner had a better result with the reference shoe.
We then aggregated the data for all runners in one graph. There was one small problem since some of the runners had done 25 minute test runs and others 30 minute. We stretched the 25 minute runs to 30 minutes and filled in data between the missing points. This means that if all test runs had been 30 minutes we would have probably had a bit bigger overall difference between the shoes. Since everything points to that, the difference gets bigger the longer the run. For this pilot we feel this is sufficient.
The aggregated data shows a clear difference between the test shoe and the reference shoes. In the end, there is about a 5 beat per minute difference. This indicates that for this test group, the test shoe was more energy efficient than the reference shoes.
Next step and final thoughts
The goal of this pilot study was to determine if the test could show differences between shoes. In our earlier studies we had made this type of comparison only on a group level. This recent test has the ability to compare the results of many runners each doing just two runs, as shown above. Perhaps more important is that the test can be done on an individual basis, since it is easy to do by yourself and it doesn’t take a huge effort. You can do the test several times in just one week and get enough data to compare your individual energy efficiency in different shoe models. We know that is important since we have witnessed huge individual differences in how much benefit one can have from different shoes.
We are aware that these findings are worth exploring further. We will do a bigger study featuring at least 100 runners. At best we could start a trend in which we can inspire runners to compare different shoes and share the data from which everybody could benefit.
Click here to see the Airia Heart Rate Test Data collected.
Running Shoe Comparative Heart Rate Pilot Study