Fig 1.
a) Skiing trajectory of a random run, b) profile of the trajectory and c) gate distance definitions.
Blue line presents the skiing trajectory. The start, the finish and the gates are denoted as red dots.
Fig 2.
a) A skier during the measurements.
b) The custom-built Real-Time Kinematics Global Navigation Satellite System (RTK GNSS) including helmet.
Fig 3.
Skier positions along a ski turn including the trajectories of his centre of mass (COM) and of the midpoint between the ankle joints (MAJ).
In the skier’s positions within the ski turn (positions from 2 to 4) also the tangential , normal
and binormal
unit vectors of the MAJ trajectory are annotated.
Fig 4.
Two-point skier model including the trajectories of the centre of mass (COM) and of the midpoint of the ankle joints (MAJ).
and
represent the velocity vectors of the COM and of the MAJ, while
presents the velocity vector of the COM relative to the MAJ.
is the gravity,
the air drag and
the ground reaction force vector.
is the skier activity force transmitted by between the MAJ and the COM.
Fig 5.
Average specific mechanical powers of the gravity (, green), air drag (
blue), inertial force (
, red) and of the ground reaction force (
, black) at the skier’s COM within a ski turn.The curves represent the mean for five subjects and the shaded area its standard deviation (± SD). The duration of the ski turn is given in percentage of the ski turn cycle. The vertical black line represents the gate position. At the top of the figure relevant stick figures of the skier are shown.
Fig 6.
Average specific power resulting from the skier’s activity (, red), including the specific mechanical power resulting from the ground reaction force at the skier’s MAJ (
, blue) and at the COM (
black) within a ski turn.
The curves represent the mean for five subjects, and the shaded area its standard deviation (± SD). The duration of the ski turn is given in percentage of the ski turn cycle. The vertical black line represents the gate position. At the top of the figure relevant stick figures of the skier are shown.
Fig 7.
Average specific mechanical power resulting from the skier activity in the tangential (, black), normal (
, blue) and binormal (
, green) directions of the MAJ trajectory within a ski turn.
The curves represent the mean for five subjects, and the shaded area its standard deviation (± SD). The duration of the ski turn is given in percentage of the ski turn cycle. The vertical black line represents the gate position. At the top of the figure relevant stick figures of the skier are shown.
Fig 8.
Specific mechanical work (SMW) of the two-point skier model performed over a ski turn.
a) Total SMW. b) SMW performed in the skiing direction. Abbreviations: — SMW resulting from the skier activity,
— SMW of the air drag;
— SMW of the ground reaction force (GRF);
— SMW of the gravity force;
— SMW of the inertial force. t index refers for the work performed in the tangential direction of the trajectory of the midpoint between the ankle joints (MAJ), i.e., in the skiing direction. Plus (“+”) and minus (“-“) signs refer to positive and negative mechanical work.