When is walking ‘faster’ than running?
Ultra-running, traversing any distance longer then a marathon on your own two feet. Some call it crazy, others call it a good day out! But what I don’t think anyone would dispute is the immense challenge that it presents. Time-on-feet, terrain, nutrition, navigation, injuries and ailments, the list goes on.
I’ve heard it a few times, people asking ‘did you run the whole way?’. As if walking should in some way detract from the sense of achievement that comes from the completion of each event. I’ve had a discussion with numerous other athletes around the duration of an event and how it varies from the front of the race to the back. In some 100 mile events, the guys bringing up the rear of the race can spend over twice as long out there. I’m in awe of these feats of incredible endurance and gritty determination, not critical of how they achieved it. If anyone on course is entitled to walk then its these folk.
I was watching Killian Jornet’s recent attempt at his fastest vertical kilometre (VK) and what do I see? The greatest mountain runner of all time walking/power hiking, whatever you want to call it, up the trail. If that isn’t confirmation that walking has its place in the trail and ultra running worlds then I don’t know what is.
This latter point got me thinking - at what incline does walking actually become favourable to running from an energetics point of view? I add that last caveat to the question because it’s tempting to just say ‘all of them’! But assuming Killian’s not doing it wrong (a relatively safe assumption) then there must be a point when running is no longer beneficial.
Let the science do the talking
Giovanelli et al (2016) put 15 trained mountain runners on a treadmill. They kept the vertical velocity at a constant (0.35m/s or 4min45 to climb 100m) but varied the treadmills gradient and the speed that the athletes ran. In other words, when the treadmill was at a lower gradient the athletes ran faster to equal their ascent on higher gradients. The runners performed the protocol twice, once running and once walking. They measured the metabolic cost of moving to determine when walking was more efficient than running and vice versa
They found three things:
At between 9% and 15% walking becomes more efficient than running
The athletes felt uncomfortable walking at lower gradients and it wasn’t until 20% when they reported it feeling natural
Energy expenditure for both running and walking is minimised on gradients between 20% and 35% - if you’re going to pick a VK race, pick one with gradients in this realm!
Take home
This tells me that when gradients get near 15%, start walking. If moving at the same speed, this will be more efficient allowing me to preserve energy for later in the race or training run. This is important to be aware of because our internal ‘walkometer’ generally doesn’t get it right. It will tell us to run on climbs when walking is more efficient. Of course, for any of this to be relevant we need to actually know what a gradient of 15% looks and feels like. One way to do this would to find a Strava segment with a relatively steady gradient in that region and go hike it. Or run with a protractor stashed in your pocket, it’ll be like being in year 7 all over again!
Other thoughts
1) In my recent blog post, ‘Finding my inner Killian’ I discussed the energetics of running uphill. The paper I discussed highlighted that at about 15% the factors determining uphill running velocity change. Then here, 15% is a gradient where walking becomes favourable to running. A coincidence? I don’t think so! When the stretch-shortening cycle of running is removed (as it is on steep inclines) then it is no longer as efficient giving walking the advantage.
2) On flat terrain, the distinction between walking and running is generally made by determining whether two feet touch the ground at any point. If they do, you’re walking. On steep inclines, it’s slightly different because both gait cycles will have two feet touching the ground at some point. Instead, they are differentiated by stride length and cadence, running being characterised by bouncier, shorter stride and higher cadence. This is sometimes referred to a ‘grounded running’.
3) In this case, they studied ‘competitive mountain runners’. There wasn’t any quantification of what this meant in terms of VO2 max measurements or competitive achievement. This means it’s difficult for us to extrapolate this out to a larger athletic population. It could be that the gradient at which walking becomes beneficial varies greatly amongst us depending on leg strength, aerobic capacity and VO2 max. As such, we need to take it with a pinch of salt and use our initiative to decide how to implement it. I’m going to take the general opinion that power hiking on lower gradients than I traditionally do will be beneficial to preserving energy later in a race. Perhaps a bit of trial and error to see what works best for me and I could really improve over long distances. Keep me posted if you try this out and how it goes.
References
Giovanelli. N, Ortiz, A, Henninger. K and Kram. R (2016). Energetics of vertical kilometer foot races; is steeper cheaper? Journal of Applied Physiology, 120: 370-375
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