Fig 1.
Representation of the three main skating sub-techniques (G2, G3 and G4), and their corresponding temporal events: Pole and ski initial contact (PON and SON), final contact (POFF and SOFF); and inner-cycle phases: Pole and ski contact time (P_CT and S_CT) and swing time (P_SW and S_SW), as well as cycle time (S_CY).
The dark colour of legs and poles illustrate the contact with the ground.
Fig 2.
Experimental setup, showing the treadmill, the inertial measurement units (IMUs) attached to the wrist and to the skis (white arrows), the reflective markers, and a camera in the background.
Detailed axis definition for the IMUs is also provided.
Fig 3.
Pole (A) and ski (B) event detection both from the reference system and from inertial measurement units (IMU) for the G3 sub-technique. ● and ■ indicates initial and final contact for the reference system, ▼ and ▲ indicates initial and final contact for the IMU system.
Fig 4.
Decision-tree for sub-technique (G2, G3 and G4) determination.
NaN means undetermined category, PON is the pole initial contact, POFF is the pole final contact, SON is the ski initial contact and SOFF is the ski final contact.
Table 1.
Number of events detected by the infrared camera reference system (REF), and the percentage of events (%) detected by the inertial measurement units (IMU), as well as the number of cycles sub-technique correctly assessed.
Table 2.
Time differences between the temporal events determined using a reference system (multiple infrared cameras) and using inertial measurement units (IMUs), as well as for the inner-cycle parameters.
Fig 5.
A: Pole initial contact (PON), B: Pole final contact (POFF), C: Ski initial contact (SON), D: Ski final contact (SOFF) inter-trials bias for Gear 2 (G2), Gear 3 (G3) and Gear 4 (G4) sub-techniques. * indicates significant pairwise differences based on an alpha level of < 5%.
Fig 6.
A: Pole contact time (P_CT), B: Pole swing time (P_SW), C: Ski contact time (S_CT), D: Ski swing time (S_SW) inter-trials precision for Gear 2 (G2), Gear 3 (G3) and Gear 4 (G4) sub-techniques. * indicates significant pairwise differences based on an alpha level of < 5%.