Tuesday, 29 May 2012

A quantification of the reduction in effort when running in lighter shoes - another test

Difference in running speed, at equal physiological effort, in lighter and heavier shoes

In a previous blog I reported a comparison of 'physiological effort' of running at the same speed in two different running shoes. I compared the ProGrid Ride (740g total weight for the pair) with the Hyperspeed (425g total weight for the pair) both UK size 9. I conducted the test on a flat tarmac track (2km at 4:50 mins per km) alternating between shoes. The result was that when using the Hyperspeeds I had roughly 1.8% fewer heart beats per km than when using the ProGrid Rides. I then went on to suggest that this might extrapolate to a 1.8% faster speed for the same heart rate.

I posted a link to the results on RunningAHEAD and JRMichler suggested a better test. He said; " The next logical experiment would be to run 1.8% faster with the lighter shoes and compare average heart rates. "

It is indeed a good idea. The last test was fixed speed, on this one I set out to run at a speed that I predicted would produce equal heart rates with both shoes. I started with the ProGrids and ran a warm-up 2km along the route (here is the run). I then set-off at 4:30 min per km pace for the first test run which I abandoned just over halfway when I turned at the wrong pole......I walked back.
The next two runs in the ProGrids were done (1 & 2) in 9:03min and 9:02min for the 2km - roughly 2s slower than I had planned. I then attempted to run ~2% faster in the Hyperspeeds. The first run was in 08:51min and the second in 08:49min (2.14% faster than in the ProGrids).

In Figure 1 I have plotted the speed (in km per hour) and the heart rates for each run.

Figure 1. Speed and heart rate data for six runs (in sequence) on a 2km flat tarmac path in two different running shoes. The first run was done at an average of 137 beats per minute (as reported by Garmin Training Center) whilst the next four runs were all done at 138 beats per minute. On the final run my heart rate was 1 beat per minute higher. I have set the y-axis ranges to allow the difference in heights of the individual bars to be judged. I am not attempting to imply either a large or a small effect - it is ~2%.
I shall restrict my analysis to the middle four runs for a couple of reasons. First, the middle Hyperspeed runs are bracketed ProGrid runs making for a symmetrical arrangement. Second, all of those runs resulted in the same heart rate (138 beats per min). The average speed for the middle two ProGrids was 13.30 km per hour and for the Hyperspeeds it was 13.58 km per hour. Thus, I ran in the Hyperspeeds 2.14% faster than in the ProGrids but (to integer accuracy) the heart rate was identical. Thus, it would appear the lower heart beats per km using the Hyperspeeds in my previous test does translate to a faster speed (~2%) at the same heart rate.

For interest I have included in Figure 2 an analysis of heart beats per km for the same data set.
Figure 2. Heart beats per km for the same runs as shown in Figure 1. This form of analysis normalizes for speed and heart rate producing a value of heart beats per km that is fairly insensitive (although not completely) to speed. It shows that the Hyperspeeds require fewer heart beats to be taken per km run. The y-axis minimum is the value that I predict I would need to run a world record marathon.

This is consistent with the idea that losing 150g from each foot results in either a lower physiological effort for the same speed, or higher speeds for the same heart rate (the choice is yours!).

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