Performance-determining factors in biathlon prone shooting without physical stress.

This study investigated the most important factors determining biathlon prone shooting performance. Ten female and 16 male biathletes (age 19.9 ± 2.9 years) from the national teams of Finland and Vuokatti-Ruka Sports Academy performed 6 × 5 biathlon prone shooting shots without physical stress under laboratory conditions. Shooting performance and multiple aiming point trajectory variables were measured together with an analysis of triggering force. Based on the aiming point trajectory data principal component analysis, we identified four technical components in biathlon prone shooting: stability of hold, aiming accuracy, cleanness of triggering, and timing of triggering. Multiple regression analysis (MRA) further determined that cleanness of triggering, aiming accuracy, and timing of triggering accounted for 80% of mean shooting performance (p < 0.001). Better stability of hold, aiming accuracy and cleanness of triggering were directly associated with better shooting performance (0.62 ≤ |r| ≥0.79, all p < 0.001). Better stability of hold measures were also associated with better cleanness of triggering, and higher pre-shot trigger force levels were associated with better stability of hold and cleanness of triggering. These results indicate that with both direct and indirect effects on performance, stability of hold seems to be a general prerequisite for successful biathlon shooting. The results also highlight the importance of aiming accuracy, cleanness and timing of triggering, along with a high pre-shot trigger force level. The variables identified in this study could be used to assess biathletes' performance in the most relevant shooting technical aspects to guide the emphasis of their shooting training.

Validation of 2D Force Measurement Roller Ski and Practical Application.

Several methods could be used to measure the forces from skis or roller skis in cross-country skiing. Equipment that could measure medio-lateral forces may be of good help for investigating the relevant skating techniques. The aim of this study was to validate a pair of newly designed two-dimensional force measurement roller skis. The vertical and medio-lateral forces which were perpendicular to the body of the roller ski could be measured. Forces were resolved into the global coordinate system and compared with the force components measured by a force plate. A static and dynamic loading situation for the force measurement roller ski was performed to reveal the validity of the system. To demonstrate whether the force measurement roller ski would affect roller skiing performance on a treadmill, a maximum speed test with the V2 technique was performed by using both normal and force measurement roller skis. The force-time curves obtained by these two different force measurement systems were shown to have high similarity (coefficient of multiple correlations > 0.940). The absolute difference for the forces in the X and Z directions over one push-off cycle was 3.9−33.3 N. The extra weight (333 g) of the force measurement roller ski did not affect the performance of the skiers. Overall, the newly designed two-dimensional force measurement roller ski in this study is valid for use in future research during daily training for skate skiing techniques.

Propulsion Calculated by Force and Displacement of Center of Mass in Treadmill Cross-Country Skiing.

This study evaluated two approaches for estimating the total propulsive force on a skier's center of mass (COM) with double-poling (DP) and V2-skating (V2) skiing techniques. We also assessed the accuracy and the stability of each approach by changing the speed and the incline of the treadmill. A total of 10 cross-country skiers participated in this study. Force measurement bindings, pole force sensors, and an eight-camera Vicon system were used for data collection. The coefficient of multiple correlation (CMC) was calculated to evaluate the similarity between the force curves. Mean absolute force differences between the estimated values and the reference value were computed to evaluate the accuracy of each approach. In both DP and V2 techniques, the force-time curves of the forward component of the translational force were similar to the reference value (CMC: 0.832-0.936). The similarity between the force and time curves of the forward component of the ground reaction force (GRF) and the reference value was, however, greater (CMC: 0.879-0.955). Both approaches can estimate the trend of the force-time curve of the propulsive force properly. An approach by calculating the forward component of GRF is a more appropriate method due to a better accuracy.

Aiming strategy affects performance-related factors in biathlon standing shooting.

This study focused on investigating differences in shooting performance and performance-related factors between two different aiming strategies (HOLD, low radial velocity during the approach 0.4-0.2 seconds before triggering, and TIMING, high radial velocity) in biathlon standing shooting. A total of 23 biathletes fired 8 × 5 standing shots at rest (REST) and 2 × 5 shots during a race simulation (RACE). Shooting performance (hit point distance from the center of the target), aiming point trajectory and postural balance were measured from each shot. Shooting performance was similar both at REST (HOLD 33 ± 5 mm vs TIMING 38 ± 8 mm, P = .111) and in RACE (40 ± 11 mm vs 47 ± 12 mm, P = .194). Better shooting performance was related to smaller distance of the aiming point mean location (REST r = 0.93, P < .001, RACE r = 0.72, P = .018) and higher time spent within ⅔ of the distance of the hit area edge from the center 0.6-0.0 seconds before triggering (REST r=-0.88, P = .001, RACE r=-0.73, P = .016) in HOLD, and to lower aiming point total velocity 0.6-0.0 seconds before triggering (REST r = 0.77, P = .009, RACE r = 0.88, P = .001) and less aiming point movement 0.2-0.0 seconds before triggering (REST r = 0.82, P = .003, RACE r = 0.72, P = .012) in TIMING. Postural balance was related to shooting performance at REST in both groups and in RACE in TIMING. Biathletes using the hold strategy should focus on stabilizing the aiming point before triggering and aiming at the center, whereas biathletes using the timing strategy benefit of decreasing the total velocity during the final approach as well as minimizing the aiming point movement right before triggering.

Evaluation of 3D Markerless Motion Capture System Accuracy during Skate Skiing on a Treadmill.

In this study, we developed a deep learning-based 3D markerless motion capture system for skate skiing on a treadmill and evaluated its accuracy against marker-based motion capture during G1 and G3 skating techniques. Participants performed roller skiing trials on a skiing treadmill. Trials were recorded with two synchronized video cameras (100 Hz). We then trained a custom model using DeepLabCut, and the skiing movements were analyzed using both DeepLabCut-based markerless motion capture and marker-based motion capture systems. We statistically compared joint centers and joint vector angles between the methods. The results demonstrated a high level of agreement for joint vector angles, with mean differences ranging from -2.47° to 3.69°. For joint center positions and toe placements, mean differences ranged from 24.0 to 40.8 mm. This level of accuracy suggests that our markerless approach could be useful as a skiing coaching tool. The method presents interesting opportunities for capturing and extracting value from large amounts of data without the need for markers attached to the skier and expensive cameras.

Solution of atomic orbitals in an interpolating wavelet basis.

The Schrödinger equation of hydrogenic atoms and the Hartree-Fock equations of some many-electron atoms are solved using interpolating wavelets as basis functions. The nonstandard operator form is used to compute operators in basis sets including multiple resolution levels. We introduce an algorithm for converting matrices from nonstandard operator form to standard operator form. We also consider the different components of the Hamiltonian and Fock operators separately and derive analytic formulas for their evaluation. Extension to many-electron atoms is done within the Hartree-Fock formalism. Convergence of atomic parameters such as orbital eigenvalues with respect to the number of resolution levels is inspected numerically for hydrogenlike atoms (ions) and some light many-electron atoms (helium, lithium, beryllium, neon, sodium, magnesium, and argon).