This case study examines the impact of boot longitudinal flexural stiffness on the total external mechanical work of a skier`s centre of mass per distance travelled in the forward direction (W'EX (J/m)) and on running economy during skate roller-skiing under submaximal steady-state conditions. Moreover, it analyses time derivatives of total WEX, of WEX performed by the roller-skis and poles, respectively, and of the directly useful mechanical work (the sum of the work to overcome centre of mass` gravity and rolling resistance) within a typical roller-skiing cycle. Multiple roller-skiing trials (G3 technique) were performed by one subject on an inclined treadmill with boots of soft, intermediate, and stiff flexural stiffness. The orientation and magnitude of the roller-ski and pole ground reaction forces, body kinematics, VO2, and lactic acid concentration were monitored. The stiff boots had 13.4% (p < 0.01) lower W'EX compared to the intermediate boots, and 20.7% (p < 0.001) lower W'EX compared to the soft boots. Regarding running economy, the soft boots had 2.2% (p < 0.05) higher VO2 compared to the intermediate boots, but the same VO2 compared to the stiff boots. In conclusion, the soft boots had significantly higher W'EX and running economy, while stiff boots had significantly lower W'EX and intermediate boots significantly lower running economy. Moreover, W'EX appears to be a better indicator of the boot flexural stiffness impact on energy efficiency than running economy.
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