Treadmill calibration

On Saturday I was supposed to run for an hour at "CCM" which is halfway between my aerobic and anaerobic thresholds (heart rate of 167 bpm or roughly Half-Marathon pace). I decided to do it on the treadmill so, as usual, I set the incline to 1%, put on a film and set off at 15 kph. By halfway my heart rate was still in the aerobic zone (150 bpm), which is where I do all my easy and long runs. It felt like I was running fast - I was kicking my legs up high and my lungs were being forced to work reasonably hard. I had seen some impossibly low heart rate register on my watch so maybe that was what was broken... I decided to up the ante to 15.5 kph for the second half but even that was only enough to get my heart rate up to 160 bpm so, finally, I ran the last 15 minutes at 16 kph, running a total of 15.4 km in a hour. By which time my heart rate climbed to 170 bpm at the end. It was a fairly hard run but it wasn't that hard! I realized that the treadmill must be running too slowly.

I discovered that there is a way to calibrate the belt speed. I was surprised to discover that all treadmills seem to use the same trick to activate the calibration mode: while holding down the "stop" and "increase speed" buttons, you insert the key and then release the two buttons. When you ramp up the motor to 85% of it's maximum power, the treadmill should reach maximum speed - in my case it was saying 17.5 kph instead of the reported maximum of 18 kph. My treadmill appears to have an automatic calibration mode which you start by pressing the "increase speed" and "decrease speed" buttons as you insert the key. In general, all the speeds were coming out slightly lower than they should have been but I expect that the automatic calibration is on the conservative side. Imagine that somebody were to injure themselves on a treadmill and then sue the manufacturer because it was running at 9.3 kph instead of the 9 kph they had programmed!

I tried using my Garmin foot pod, which is a little device with in built accelerometers that you attach to your shoe. Firstly I calibrated it to GPS signals by running outside and then I ran (supposedly) at 16 kph on the treadmill indoors. The foot pod seems so inaccurate that I wasn't able to come to any conclusion. For example, just by exaggerating the kick under my butt, I was able to appear to run much faster even though I had not changed the speed of the belt.

It seems to me that the best approach is to do the obvious. I chalked a mark on the belt, measured the length of the belt and counted how many times the mark went past in a minute. For this I used a BPM (Beats Per Minute) calculator on my iPhone - sometimes my past life as a deejay comes in handy. By my calculations, the treadmill is about 3.5% slow. Even so, the run I did last night was at an average speed of 14.9 kph - fast enough to run 10k in a tad over 40 minutes and then another half again. Not bad for a less than medium intensity run.