Temporal–spatial parameters
The results of the temporal parameters of ski propulsion are listed in Table 1. Athlete poling with camber angle of 24° had the smallest CT (t = 1.53 ± 0.17 s) and PT (t = 0.73 ± 0.07 s). The results revealed that the abduction angle affects the cycle distance, in detail, the cycle distance with poling camber angle of 24° (1.07 ± 0.12 m, P = 0.029) and 30° (1.11 ± 0.13 m, P < 0.001) were significantly larger than 0° (1.02 ± 0.14 m) (Fig. 2A).
Cycle distance and output power of different poling camber angles. Cycle distance (A), output power (B), effective output power (C) of the double poling cycle in 30-s experiments.
Results in Fig. 2B show that output power increased with the increase of poling camber angle at 15° (597.78 ± 150.31 J), 24° (610.94 ± 158.96 J, P = 0.011) and 30° (629.10 ± 168.78 J, P < 0.001) compared with 0° (590.65 ± 148.95 J). And result show that effective output power decreased with the increase of poling camber angle at 15° (577.41 ± 145.18 J), 24° (558.12 ± 145.22 J, P = 0.011) and 30° (544.82 ± 146.17 J, P < 0.001) compared with 0° (590.65 ± 148.95 J).
Maximum range of motion and joint moment
Joint kinematics showed that elbow and spine flexion were affected by the poling camber angle during the DP, while shoulder flexion was not (Fig. 3A–C). When athlete performed DP with poling camber angle, the elbow flexed more at the start of the poling phase (Fig. 3B), and the range of motion (ROM) of elbow and spine flexion also increased. Specifically, elbow ROM of poling camber angle at 24° and 30° were significantly higher than the other poling camber angle (0° vs 15°, P < 0.001, 0° vs 24°, P < 0.001, 0° vs 30°, P < 0.001, 15° vs 24°, P = 0.032, 15° vs 30°, P = 0.002). The ROM of spine flexion was increased with the poling camber angle (0° vs 24°, P < 0.001, 0° vs 30°, P < 0.001, 15° vs 24°, P = 0.037, 15° vs 30°, P < 0.001, 24° vs 30°, P = 0.021). ROM of pole angle was also increased when athlete performed DP with poling camber angle (0° vs 24°, P = 0.025, 0° vs 30°, P = 0.013, 15° vs 24°, P = 0.026) (Table 2).
Joint angle and joint moment of shoulder, elbow and spine during the double poling (DP) cycle in cross-country sit-skiing. (A–C) Joint angles of shoulder flexion (A), elbow flexion (B), and spine flexion (C). (D–F) Joint moment of shoulder flexion (D), elbow flexion (E), and spine flexion (F). All angles are measured in degrees and are presented for 100% double poling (DP) cycle.
Joint kinetic results revealed that the peak flexion moments of shoulder and elbow occurred at the later stage of the PP (Fig. 3D,E). The peak flexion moments of shoulder (0° vs 15°, P = 0.003, 0° vs 24°, P = 0.009, 0° vs 30°, P = 0.01), elbow (0° vs 15°, P = 0.007, 0° vs 24°, P = 0.001, 0° vs 30°, P = 0.007), and spine (0° vs 30°, P = 0.002, 15° vs 30°, P = 0.034) increased with the poling camber angle increased when athlete performed DP. The peak flexion moments were not significant changed when the poling camber angle increased from 24° to 30° for both shoulder and elbow joints (Fig. 3D–F, Table S1).
Muscle activation and muscle force
Average muscle activity (aEMG) and the muscle activity peak (EMGpeak) data were reported as mean ± SD in the Table 3. Both aEMG and EMGpeak values of shoulder joint muscles increased when poling camber angle increased. Specifically, for poling camber angle of 24° or 30°, aEMG value of the Antdelt (0° vs 24°, P = 0.033, 15° vs 24°, P = 0.025), Middelt (0° vs 24°, P = 0.021, 0° vs 30°, P = 0.044), Postdelt (0° vs 24°, P = 0.03, 0° vs 30°, P = 0.034), Bic (0° vs 30°, P = 0.016), Tric (0° vs 30°, P = 0.049) and Infra (0° vs 30°, P = 0.049) increased significantly, and EMGpeak value of Antdelt (0° vs 24°, P = 0.028), Middelt (0° vs 24°, P = 0.04, 0° vs 30°, P = 0.044), Postdelt (0° vs 30°, P = 0.023), Bic (0° vs 24°, P = 0.04, 0° vs 30°, P = 0.045) and Tric (0° vs 24°, P = 0.048, 0° vs 30°, P = 0.043) increased significantly.
SO was used to calculate the muscle forces during the DP, and the maximum muscle forces during the DP process are displayed in Fig. 4. Postdelt, Bic, and Middelt generated the greatest average forces over the six DP cycles with or without the poling camber angle. In addition, maximum muscle forces of Antdelt (0° vs 15°, P = 0.005, 0° vs 24°, P = 0.023, 0° vs 30°, P = 0.046) and Bic (0° vs 15°, P = 0.003, 0° vs 24°, P = 0.001, 0° vs 30°, P < 0.001, 15° vs 24°, P = 0.04, 15° vs 30°, P = 0.031) significantly increased with the increase of poling camber angles.
Maximum muscle force estimated during the double poling (DP) cycle. *Represents a significant difference compared to 0°; †represents a significant difference compared to 15°; #represents a significant difference compared to 24°. *,†,#p < 0.05, **,††,##p < 0.01. Anterior deltoid (Antdelt), Middle deltoid (Middelt), Posterior deltoid (Postdelt), Biceps brachii (Bic), Triceps brachii (Tric), and Infraspinatus (Infra).
Shambhu Kumar is a science communicator, making complex scientific topics accessible to all. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
