The effect of exercise intensity on speed and heart rate profiles, work rate and kinematics in skating cross-country skiing
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The exercise intensity during cross-country skiing competitions fluctuates. However, it is presently not known to what extent this occurs during ski-specific training at the different intensities. The aim of the present study was to investigate the actual speed and heart rate profiles, work rate, and gross kinematic patterns. Seven elite male junior cross-country skiers were initially tested for peak oxygen uptake during treadmill roller ski skating in the laboratory. Thereafter, on a separate day, the skiers performed two 20-m maximal velocity tests in both uphill and flat terrain. The main experiment consisted of three 5-km of skiing with the skating technique in a competition track on snow at low- (LIT), moderate- (MIT), and high-intensity training (HIT) using a heart rate monitor and an inertial measurement unit (IMU) coupled to a global navigation satellite system (GNSS). Main findings were as follows: 1) the average racing speed, the relative heart rate and work rate increased with higher exercise intensity (P <0.05), and the differences was higher between MIT vs. LIT than MIT vs. HIT (P <0.05), 2) there was a shift in the delayed heart rate response, and the effect was larger with higher intensity, thus limiting the possibility for recovery during higher intensity, 3) more than half of the total time in all intensities was spent uphill, 4) the uphill sections were responsible for the greatest performance differences during HIT (P <0.05), 5) G2-Vmax correlated strongly with speed uphill HIT (r = 0.78, P < 0.05). Cross-country skiing in terms of speed, external work, metabolic intensity, and kinematics are clearly interval based, which makes ski-specific training in varying terrain unique. Hence, the effect of exercise intensity must especially be taken into account during training in cross-country skiing.