Sunday, 25 October 2015

Half marathon, XC, and other races

After the race, Heather and I enjoying the valley view
On Thanksgiving Sunday I awoke at 5:15 am, ready, more or less, to finish the last of three races in the first annual RNS Performance series*. Race number 1, the Lung Run 5k was won in May with a time of 15:08 just ahead of Cal DeWolfe. Race number 2 was the Natal Day 6 miler, which I lost to Matt McNeil.

Neither Cal nor Matt were registered for the Performance series, so I knew going into the last race it was pretty likely I would win outright. Still, I had no plans to run slack. But neither was I sure it'd be a solid race. Strange thing about running is that the language used to describe your body, legs, mind, etc are in their infancy. Doesn't help either that the feelings you have before doing well seem eerily similar to ones before a lousy run. It can sometimes come down to voodoo and the like.

My goal for the race series had always been to run it under two hours. In other words 5k + 10k + 21.1k = 36.1 km of running, so to complete that in two hours means averaging 18 km/h. My cumulative time until Sunday morning was 47:22, well within reach, balanced by knowing too that a sub 73 minute half is never 'trivial'.

Sunday, 4 October 2015

Racewalking: The hidden flight path

Anyone who has watched racewalking intuitively knows it's different from running, hence it has as much credibility as classic technique in XC skiing, or the butterfly stroke event in swimming. And anyone who's tried race-walking knows it's very hard to do well, painful (especially the shins) and frustrating (especially if you get DQd moments before finishing). For most of its contemporary existence it has been a maligned sport.

What are the technical differences between walking and running? According the official rules,
  • Racewalking is a progression of steps so taken that the walker makes contact with the ground so that no visible (to the human eye) loss of contact occurs.  
  • The advancing leg must be straightened (i.e., not bent at the knee) from the moment of first contact with the ground until in the vertical position.
We know there is a flight phase with each running step. Walking, by contrast, both your feet should never both leave the ground. Rule #2 is less intuitive but in fact a better way to differentiate running versus walking. Interestingly this rule only came into effect in 1995.

There are another technical differences. For instance in a runner's mid-stance phase, i.e. when the foot swivels under the hip, the body's centre of mass (COM) is at its lowest. For walkers, because of the straight knee, their mid-stance COM is at its highest point. I only mention this because because I find that both running and walking, when you really think about them, are weird, complex movements.

Returning to rule #2, it is easy enough to visualize (and enforce) to make it a fair visual criteria in a judged sport. However there is a fundamental problem with Rule #1 that I will now explain. There is already plenty of research that observes a flight phase in race walking. For instance in a recent (2014) literature overview, Pavel et al note
From an overall view, race walking athletes seem to adhere to the ‘straightened knee’ rule, but at race speed they do not observe the ‘no-flight time’ rule. 
Admittedly flights times spoken of are small; Pavel estimates between they range 0.01 and 0.05 seconds. But those small flight times add up. Moving at 4 m/s, a single 1/100th second of "flight time" can earn a bonus distance of 4 cm (after all, distance = speed x time). So in a 50 km walk race, given a stride frequency of 3 steps/s (180 steps/min), one takes over 37,000 steps. That tiny flight time and 4 cm per stride adds up to a total distance gain of 1.5 km! Importantly the human eye cannot visually process a flight time of 10 milliseconds yet a race walker is less likely to win without this clear flight-time advantage. Indeed, in one study flight times were found positively correlated with speed.

Video of a race-waller leaving the ground (at 0:13):

Unlike some judged sports where small "cheat" advantage stay small (such as making a single illegal V-shape move with your skis in classic racing), because of the cumulative effects of undetectable millisecond flight times, we now know a completely honest race walker is at a permanent disadvantage over one who can eke out a bit of air time for each stride.