What is the influence of weight on performance?

Saving weight when ski touring has always been one of the biggest debate in the sport. Should you try to save weight at any cost and maybe sacrifice some comfort and some security? When it comes to skimo racing, ultralight gear became the norm for athletes but when talking about amateurs, the differences in terms of gear are sometimes big. This article aims to look at how important is the role played by our gear’s weight. Should we aim for the lightest gear possible or not?

RUNNING ECONOMY (RE)

When talking about performance in endurance sports, there really are only three physiological components that will determine your race time. We already talked about them throughout others articles but let’s talk about them again. These three components are:

• VO2max
• Thresholds (VT 1 and VT2)
• Running economy

It is obvious that your gear won’t have any effect of your VO2max nor on your thresholds but, according to science, when talking about running or hiking, reducing your shoes weight has an impact on your running/walking economy. It goes the same way with cycling economy so one could argue that this trend also applies to ski-mountaineering.

HOW IMPORTANT RUNNING ECONOMY REALLY IS?

There has been many studies highlighting the impact of a reduced running economy on endurance performance. As an exemple, one study from Hoogkamer et al. (2016) found that even small (1 to 3%) changes in RE can lead to up to 3% change on a 3000m run time trial. And guess how they did manage to reduce running economy of their subjects? By increasing their shoes weight by 100g and 300g for both test groups. By doing so, they showed that even small increase in terms of shoe weight can lead to significant decrease in terms of RE and therefore in terms of race performance. In fact, scientists were already interested by this topic all the way back in the 80s. Myers et Steudel (1985) showed that 1kg added to the upper body can lead to an increase of 1% of oxygen demand and the same mass added to lower limbs can increase it to up to 10%.

Based on these results, one can understand that gear weight have a significant impact on performance and, in these studies, we are talking about level running so gravity does not play the same role as in uphill moving.

Talking about uphill moving, this field has been largely studied in cycling. Di Prampero et al. (1979) introduced the following equation to calculate the power necessary to cycle uphill:

W = krMs + kaAsv² + giMs

Where:

• W = power
• kr = the rolling resistance coefficient
• M = the cyclist + his gear mass
• s = speed (without taking wind into account)
• ka = air resistance coefficient
• A = frontal area
• v = speed (taking wind into account)
• g = gravitation acceleration constant
• i = slope incline

We’re not going to discuss this equation in detail here but we can still use it to extrapolate what’s going on in ski-mountaineering. When using race skins that provide excellent glide such as the Pomoca Race Pro 2.0 combined with a small contact surface, kr (which in skimo would correspond to friction forces between the skin and the snow) will decrease significantly. The other major component that we can easily modify to our advantage is, you guessed it, mass. In this equation, mass is directly multiplied by the slope incline. Therefore, the steeper the climb, the more costly your gear weight will be.

To our knowledge, no study has ever tried to calculate the true cost of gear weight in skimo, be it through energy expenditure or through power calculation. Therefore, we can only speculate and extrapolate what has been done in other activities but this still highlights the preponderant role that mass plays in uphill locomotion.

Below is a table summarizing the major weight savings when using racing gear compared to normal ski-touring gear. As discussed above, weight applied to lower limbs has much more impact on RE. The table therefore focuses on lower limb gear.

This table compares ultralight racing gear with traditional ski touring equipment.

This table illustrates clearly the massive differences between both set ups in terms of weight. Without even talking about the greater range of motion of racing shoes or the fact that having thinner and shorter skins provide much better glide and therefore less energy expenditure (i.e better RE), one can easily guess that much lighter gear means way better RE.

WHAT ABOUT CONFORT AND REFUELING?

Although weight significantly impacts performance, it's imperative to carefully consider what items to lighten. This is especially crucial for a race as long as the Patrouille des Glaciers, which takes place predominantly at night, cold and at high altitude. It's essential not to prioritize weight reduction over comfort, as it could potentially have adverse effects and jeopardize the race.

Clearly, saving weight should not come at the expense of refueling too. While water may be heavy (1L of water weighs nearly the same as a pair of skis), its influence on performance is just as important as weight itself. A minor dehydration (induced solely by thermoregulation) reduces aerobic performance with effects on muscle strength and endurance (Barr, 1999).

Similarly, the same principle applies to clothing. The body expends a lot of energy to combat the cold. If you choose the right balance between lightness and comfort/warmth, you'll save valuable energy during the night, which will be greatly appreciated on Lac des Dix.

IN SUMMARY:

Weight significantly affects endurance performance. However, it's crucial to strike the right balance between weight savings and comfort. Do not overlook your clothing, and certainly not your refueling. This could have more negative consequences than benefits. In terms of ski-mountaineering gear, however, everything seems to indicate that the lighter is the better in terms of performance.

To learn more about influence of gear weight on endurance performance:

• Balducci, P., Clémençon, M., Morel, B., Quiniou, G., Saboul, D., & Hautier, C. A. (2016). Comparison of level and graded treadmill tests to evaluate endurance mountain runners. Journal of sports science & medicine, 15(2), 239.
• Barr, S. I. (1999). Effects of dehydration on exercise performance. Canadian Journal of Applied Physiology, 24(2), 164-172.
• DiPrampero PE, Cortili P, Mognoni P, Saibene F (1979). Equation of motion of a cyclist. Journal of Applied Physiology 47, 201-206
• Hoogkamer W, Kipp S, Spiering BA, Kram R. Altered Running Economy Directly Translates to Altered Distance-Running Performance. Med Sci Sports Exerc. 2016
• Fuller, J.T., Bellenger, C.R., Thewlis, D. et al. The Effect of Footwear on Running Performance and Running Economy in Distance Runners.
• Myers, M. J., & Steudel, K. (1985). Effect of limb mass and its distribution on the energetic cost of running. Journal of Experimental biology, 116(1), 363-373.
• Rodrigo-Carranza V, González-Mohíno F, Santos-Concejero J, González-Ravé JM. Influence of Shoe Mass on Performance and Running Economy in Trained Runners. Front Physiol. 2020