Sunday, November 18, 2018

GPS Inaccuracy is a Non-Problem

There are those who say running is not a skill. Sure, unlike soccer or archery, it may not need massive amounts of skill but the ability to pace by the internal "calibrator" in your head is absolulely a learned skill. That takes long hours of practice and generous amounts of emotional intelligence. Some people have more of EI than others. Perhaps women are better long distance pacers for this reason? The debate continues.

The other day, I ran a relatively decent 10K with a simple tried-and-true method I always employ : hit kilometer landmarks at specific times. The race, an annual staple in the Abu Dhabi calender, is not AIIMS certified, but is run on a course that is reliable enough for most of us 8am-5pm working animals. The course is also an easy out and back with stretches of long road and one roundabout so the effect of loops and not running tangets around those loops is absolutely minimal. 

The trusted V800 GPS on my wrist always goes as a supplement, never a primary mode of pacing. Not surprisingly, the device would beep the kilometer split on-point in the beginning  stretches of the race (corresponding to the position of kilometer signage) but as the race progressed, anywhere between 10-20 metres before the marked landmark.

It's important to put this into perspective. At my running speed, the watch beeped 3-5 seconds before the actual km marker.  Over the course of 42:08 minutes, I ran 10.17km according to the watch but the race distance was reported to be 10km.  In other words, assuming that the course was marked out correctly, the receiver on my wrist relying on a system of 24 global positioning satellites in orbit would under-report distance by 1-2%. 

Is that really something to make a big hoopla about?

Don't Fuss, We're Finely Tuned Machines

An experienced 10K road runner running would be consistently pacing within 1-5% of previous timings from race to race. They really are fined tuned machines.  They already an ingrained sense of pace from long hours of training and racing. The GPS doesn't come to much benefit except to help assess whether they are roughly where they need to be. 

A beginner road marathoner on the other hand might be more reliant on the GPS. They feel they need the training wheel to help guide them along, perhaps more out of a sense of anxiousness that anything can go wrong on such a long distance if they were off from where they need to be. 

I argue that even these second class of individuals don't really need to depend primarily on GPS pace. With lots of hours of correct training, the human brain learns the forces and patterns of a marathon pace most comfortable and sustainable for a period of 2-4 hours. The primary reason for the trepidation in these runners is lack of adequate training. It's not GPS thats the problem.

Get a Hold of Precision, not Inaccuracy

In a review of a ridiculous measurement of the same segment of road measuring 10km around 1000 times by GPS, the German mathematician Helmut Winter (who was also responsible for creating the timing systems in Kipchoge's world record Berlin marathon) wrote on his blog : "The most important result of the analyses was a standard deviation of the distribution of about 2 m for a total distance of 10,000 m, ie a relative dispersion of the data of about 0.2 per thousand. The deviation from the mean of the measured distance was less than 10 cm in the regime."

Even during training, I argue that a minor device deviation is a non-factor if you knew that it was precisely off everytime. 

For example, if the watch says you run 7:57 min/mile but you covered really only about 3.75 miles in 30 minutes, you know that you really ran 8:00 min/mile so the watch over-estimated pace by about 3s/mile everytime. Over the course of a 3:30:00 marathon, the actual difference between what you actually ran and what the watch says you ran is a mere 150-200m.

On race day, even with tired bodies and weather fluctuations, such a runner can turn to the biological calibrator as primary guide and use a supplemental strategy of running every mile 3s/mile faster than what the watch should actually say in order to accomodate for the margin of error.

Physiology is Not That Fussy

What about those who think if you don't hit training paces point blank, the sky will come crashing down?

Physiological reality is that there is an upper bound and lower bound to most training zones. A 20s/mile tolerance band to a threshold zone would be considerably more than the 3s/mile deviation in your GPS. Moreover, it is far better to incorporate multipace training to get your feet wet and learn different aspects of the water being tested.


We forget that the point of training is to roughly hit the bullseye everytime and get on with life. Multipace training was how the Olympic stars of previous years broke world records! Instead, some hobby runners today want military grade accuracy, perhaps to land a missile in a specific spot of an ocean somewhere with a $500 watch. They can't sleep if device reported distance was off by 2%.

My argument is that trained humans are fined tuned machines to begin with. Distance road runners (which comprise probably 80-90% of the running population) can gain a ingrained sense of sustainable pace from long hours of training.

GPS inaccuracy is really a non-problem. What is a problem is that it is turned into a problem by those looking to dip into your pocket while marketing their own product. And one has to be wary about such hidden agendas. 

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