The influence of boot longitudinal flexural stiffness on external mechanical work and running economy during skate roller-skiing: A case study

Abstract

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 ( $\overline{W}$ _EX (J/m)) and on running economy during skate roller-skiing under submaximal steady-state conditions. Moreover, it analyses time derivatives of total W _EX , of W _EX 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 $\overline{W}$ _EX compared to the intermediate boots, and 20.7% (p < 0.001) lower $\overline{W}$ _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 $\overline{W}$ _EX and running economy, while stiff boots had significantly lower $\overline{W}$ _EX and intermediate boots significantly lower running economy. Moreover, $\overline{W}$ _EX appears to be a better indicator of the boot flexural stiffness impact on energy efficiency than running economy.