Gear – Foot Weight

The ISMF had an interesting statistic in their Skimo World Championships Preview document released earlier this season. They claim 1 gram lost from feet is like losing 7 from the pack in terms of energy cost. I can’t find any data to support this but do have some thoughts as I try to cut my foot weight.

A recent study by researchers in Colorado examined the energy cost of barefoot vs. shod running. They calculated a 1% increase in VO2 per 100g weight per foot. With an approx. 540g decrease in weight per foot I should expect my VO2 to be 5.4% lower at a given speed. Thats not huge but definitely a significant improvement. Cadence will also have an effect on this; as cadence increase, the cost to move the weight will go up as shown by the scientists at the Army’s environmental and exercise research lab – USARIEM.

Dynafit’s top of the line skimo race boot is the Dy.N.A. Evo. With a carbon fiber cuff and a Grilamid shell the Evo is exceptionally light. In weight, think of it more in terms with a nordic ski boot rather than an alpine boot.  A rather unscientific analysis of some race and interval data does a good job of illustrating just how light it is.

The figure below has HR on the x-axis and vertical speed on the y-axis. Blue circles are climbs with the TLT5 boots and red squares are climbs with the Evo boots (both using Dynafit PDG skis). Each has a trendline to show the average. (TLT data are from the races in Jackson Wy earlier this season and a more recent interval workout. Evo data are from Vertfest climbs and an interval workout)

While other factors definitely affect this relationship (skins, snow conditions, fitness, other racers, track angle, etc…), there is clearly a trend. For any given HR, I am climbing significantly faster wearing the Evos. At a vertical speed of 16m/min for example, with the TLTs my HR would be around 180. With the Evos at the same speed, HR is around 145.

Now that I am running more efficiently, not working as hard on climbs, the logical next step is to climb faster maintaining the same high heart rate with an even higher speed. I have found this difficult however. Technical skinning does require skill and leg strength and while I am working less hard, I find it hard to increase my speed without slipping. I also find it hard to maintain the necessary cadence at increased speeds. I am hoping that slightly easier angled skin tracks will make the next few races more to my suiting than the steep mogul climbs from the last few races.

An interesting research project would be to examine the effects of foot weight at different cadence and track angles found in skimo racing.

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