Any skier knows that what we do is a full-body sport. After a race or a training session, your legs will be tired – but so will your arms, and maybe your back and your core, or many more specific and sometimes illogical muscle groups that got a workout.
But being a full-body sport doesn’t mean that all of these muscles are contributing equally. In fact, there are some cheaters: your arms. Earlier this year, a team from the University of Salzburg in Austria and Mid-Sweden University in Östersund, Sweden, set out to further investigate something suggested by previous research: that the arms just aren’t as efficient at extracting oxygen during exercise. Their results in double-poling strongly supported this existing pattern of research.
All of this is despite the fact that trained endurance athletes are known to be better at extracting oxygen from the blood to their muscles, which contributes to efficiency. The ability to send more blood coursing around the body with fresh oxygen helps, but the ability of muscles to extract that oxygen is also important. If there isn’t oxygen available, then muscles can’t use it – and in aerobic exercise, they need to use it. Oxygen is an essential input in the process that breaks down glucose into ATP, little energy-blocks for muscles to run on.
So what does it mean for skiers, who rely on both arms and legs to propel themselves themselves through the snow? Perhaps, a change in technique. After exploring some mechanisms for what was limiting oxygen extraction by the arms, the researchers found that the same characteristics of double-poling that were found in the fastest skiers also allowed arm muscles the best chance to overcome their limitations and gobble up more oxygen from the bloodstream.
Why Are Arms So Inefficient?
For some reason, the arms just aren’t as good at extracting oxygen as the legs are. It’s not a ski-specific problem, having been demonstrated in studies that assessed arm-specific and leg-specific exercises separately and as part of other full-body activities. And it’s a matter of debate whether or how much training even helps – some studies have found that upper body training increases oxygen extraction significantly, but others have found that it doesn’t make much of a difference.
For skiing, oxygen extraction by arm muscles depends to some extent on the technique. Take, for instance, a 2010 paper by the same authors: Glenn Björklund, Thomas Stöggl, and Hans-Christer Holmberg. They studied oxygen extraction in the arms and legs during diagonal striding, using nine elite-level male skiers and a rollerski treadmill. The team found that at both threshold and maximal effort, arms had lower oxygen extraction and higher lactate levels – but that after reducing the effort, lactate was cleared from arm muscles faster.
In diagonal striding – which we often consider to be a leg-heavy technique – the arms still generate over half the body’s propulsion. But the force generated by the legs is actually higher. As intensity and workload increases, the force from the arms stays mostly the same, while most of the gains in speed and power come from ramping up the force generated by the legs as we stomp our hardwax into the snow and drive our hips forward.
So in striding, it’s maybe not surprising that the arms don’t play as efficient a role. Even though they are important, the legs are what make a difference in speed. But what about double-poling? The 2013 study by these authors, published in the Scandinavian Journal of Medicine and Science in Sports, actually focused on this, and found some surprising results.
Even though the upper body generates practically all of a skier’s propulsion in double-poling, oxygen extraction is still lower than in the legs in this technique, and didn’t seem to change with exercise efficiency. Furthermore, oxygen extraction in the arms was, on average, lower during double-poling than in some previous studies on striding. And this was even using highly trained skiers.
Double-poling should be your arms’ time to shine, and it draws into question how important upper-body strength really is or how much long sessions of double-pole training might help.
How To Maximize Your Arms
Stöggl et al.’s most recent paper poses a possible mechanism for this drop in oxygen extraction by the arms in double poling.
First, they thought about the overall differences in oxygen extraction between arms and legs. Back in 2005, Holmberg and another team had come up with a few possibilities for causes. For instance, in the legs, there are more capillaries (small blood vessels) per size of muscle fiber. There also may be unevenness in the way that blood is distributed to different muscle groups or even to different parts of the same muscle.
More specifically to skiing, the group hypothesized that because the forces generated by the legs in striding (and skating) are greater and the time producing this power is shorter – think of a powerful push from your legs compared to the long swing of a poling cycle – the legs might have more fast-twitch muscles, which are known to be less efficient at producing ATP. As such, they need more oxygen and have adapted to extract more of it from the blood.
Next, they thought about the differences between striding and double-poling: specifically, why is oxygen extraction lower in double-poling? The force when the pole hits the snow is much higher in double-poling than in striding, and generates a lot more forward power. So the arms, which are built with more slow-twitch muscles, become less efficient. The authors proposed a mechanical hindrance to oxygen extraction: the speed of the cycles themselves limit oxygen distribution to the muscles.
This was supported by their data on oxygen extraction during recovery. If a skier was double-poling at maximal effort and then slowed down, the legs reduced their oxygen extraction and cleared the lactate that had accumulated. The arms did not. Apparently, just propelling the skier along, even at an easier pace, is enough to inhibit oxygen extraction by the arms.
This, along with the fact that more training did not necessarily mean better oxygen extraction, isn’t exactly great news for hardworking racers. But in the final portion of their study, the researchers did find something interesting. The key to maximizing oxygen extraction by the arms seemed to be allowing more recovery time during the poling swing cycle. In addition, skiers who deployed their peak force later in this cycle allowed their muscles more time to develop this application of force, and then to recover.
“Skiers who exerted large and well-timed pole forces together with even less muscle activity, while generating sufficient propulsion to allow longer recovery times with even less muscle activity, could extract more O2,” the authors wrote.
They also noticed that skiers who used their legs more in double-poling – keeping the body high and extending and flexing the hips, knees, and ankles – were able to extract more oxygen from both the upper and lower body.
What is more, this is exactly the style of double-poling that several previous projects assessing the mechanics and power generation of elite skiers found was used by the fastest athletes. In other words, the best technique maximizes oxygen extraction, although of course they couldn’t make the causal link that having higher oxygen extraction by the arms was the limiting aspect in speed or caused the improvements.
In short? Just training your upper body for strength or endurance may not really overcome some of the physiological constraints on getting those muscles to work well. But spending some long hours double-poling, as long as the focus is placed on good, efficient, and powerful technique, may enable physiological improvements, too.
Links to the Research Papers
Bjorklund, G., Stoggl, T., and Holmberg, H.C., 2010. Biomechanically influenced differences in O2 extraction in diagonal skiing: arm versus leg. Medicine and Science in Sports and Exercise 42:1899-1908.
Calbet, J.A.L., Holmberg, H.-C., Rosdahl, H., van Hall, G., Jensen-Urstad, M., and Saltin, B., 2005. Why do arms extract less oxygen than legs during exercise? American Journal of Physiology – Regulatory, Integrative, and Comparative Physiology 289:R1448-R1458.
Stoggl, T., Bjorklund, G., and Holmberg, H.-C., 2013. Biomechanical determinants of oxygen extraction during cross country skiing. Scandinavian Journal of Medicine and Science in Sports 23:e9-e20.