Abstract
In classical cross-country skiing, diagonal stride (DIA) is the major uphill sub-technique, while double poling (DP) is used on relatively flat terrain. Although, the dependence of incline and speed on the preference of either sub-technique seems clearly established, the mechanisms behind these preferences are not clear. Therefore, the purpose of this study was to compare kinetics and energy consumption in DP and DIA at the same submaximal workload in cross-country skiing under two different incline-speed combinations. We compared kinetics and physiological responses in DP and DIA at the same submaximal workload (≈200 W) under two different incline-speed conditions, (5%—12.5 km h−1 vs. 12%—6.5 km h−1) where DP and DIA were expected to be preferred, respectively. Fifteen elite male cross-country skiers performed four separate 6.5-min roller skiing sessions on a treadmill at these two conditions using DP and DIA during which physiological variables, rate of perceived exertion (RPE) and kinetics, including power fluctuations, were recorded. At 12% incline, DIA resulted in lower physiological response (e.g., heart rate) and RPE, and higher gross efficiency than DP, whereas at 5% incline these variables favored DP (P < 0.05). The skiers' preference for sub-technique (13 preferred DIA at 12% incline; all 15 preferred DP at 5% incline) was in accordance with these results. Fluctuation in instantaneous power was lowest in the preferred sub-technique at each condition (P < 0.05). Preference for DP at 5% incline (high speed) is most likely because the speed is too high for effective ski thrust in DIA, which is reflected in high power fluctuations. The mechanism for preference of DIA at 12% incline is not indicated directly by the current data set showing only small differences in power fluctuations between DIA and DP. Apart from the low speed allowing ski thrust, we suggest that restricted ability to utilize the body's mechanical energy as well as the use of arms in DP play an important role.
Highlights
Cross-country skiing is performed in varying terrain where skiers frequently make transitions between different sub-techniques
respiratory exchange ratio (RER) and RPEub values agree with this, but in double poling (DP), these variables are larger than diagonal stride (DIA) irrespective of condition
The current study aimed to investigate the underlying mechanisms behind the preferences for either DP or DIA at two different combinations of incline and speed at similar external work rate
Summary
Cross-country skiing is performed in varying terrain where skiers frequently make transitions between different sub-techniques. One of the advantages of DIA lies in the high “duty factor,” i.e., an almost continuous propulsion action by alternating ski and pole propulsion by the left—and right body sides. This leads to low fluctuations in power and speed during each cycle. The same principle applies to the poles that are fixed on the ground during propulsion, but the link from hips to the tips of the poles has a larger range of motion, allowing for higher skiing speed at which body movement speed becomes restricted This leads to increased demands on upper body power generation at higher speed. It should be noted that during races, other factors such as fatigue and/or pacing tactics will affect the choice of sub-technique at a given incline and speed
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