Contribution and effectiveness of ski and pole forces in selected roller skiing techniques on treadmill at moderate inclines

BackgroundMost of the studies about the effects of incline on cross-country skiing are related to the metabolic efficiency. The effective skiing biomechanics has also been indicated to be among the key factors that may promote good performance. The aims of this study were to provide biomechanical characteristics and investigate the relative contribution and effectiveness of ski and pole forces in overcoming the total external resistance with double poling (DP) and Gear 3 (G3) techniques at varying moderate uphill inclines.Methods10 male cross-country skiers participated in this study. Custom-made force measurement bindings, pole force sensors, and an 8-camera Vicon system were used to colle…

Biomechanics of simulated versus natural cross-country sit skiing

The purpose of this study was to investigate the biomechanics of cross-country sit-skiing in simulated and natural skiing. Thirteen international level athletes participated in a ski ergometer test (simulated conditions) and a test on snow in a ski-tunnel (natural conditions) using their personal sit-ski. Tests in both conditions were performed at individual maximal speed. When comparing the two conditions the main results were: (1) maximal speed in simulated conditions was lower (p < 0.05) but correlated well with the natural condition (r = 0.79, p < 0.001); (2) no differences in pole force variables were found; peak force (r = 0.77, p < 0.01) and average force (r = 0.78, p < 0.01) correla…

Speed control of the V2 skating technique in elite cross-country skiers

The aim was to examine how skiers control skiing speed using V2-skating. Subjects skied with three submaximal and maximal speeds on 100 m 4° uphill. Cycle variables and force parameters form the arms and legs were analysed. Cycle rate increased up to the maximum speed. Cycle length increased from the slowest speed to the all other speeds. Pole force and delta leg force increased up to the maximum speed. Ranges of motions and angular velocities of kick flexion and extension with knee and hip joints increased till highest submaximal speed. Speed was regulated with cycle length and rate while the latter was dominant after ∼5.0 m/s. Higher speed was reached with higher forces from arms and leg…

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&rsquo;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 evalua…

Force Generation Profiles of Para-Nordic Sit-Skiers Representing Different Physical Impairments

Abstract Purpose To biomechanically profile force generation connected to the complex role of the trunk in double poling in a representative sample of Para-Nordic sit-skiers. Methods Twelve male World Cup Para-Nordic sit-skiers (sport classes: LW10–12) were skiing on flat snow terrain at submaximal speed of 4.5 m/s (~ 73% maximum speed). 2D video (50 Hz) and pole force analyses (1000 Hz) were performed synchronously, examining angle, force and cycle characteristics to analyse the role of the trunk in generating propulsion. Results LW10–11.5 skiers lost between 21% and 4% propulsive force versus LW12 athletes only due to different geometrics of the trunk and pole angle at an equal axial pole…

The effect of swinging the arms on muscle activation and production of leg force during ski skating at different skiing speeds

The study investigated the effects of arm swing during leg push-off in V2-alternate/G4 skating on neuromuscular activation and force production by the leg muscles. Nine skilled cross-country skiers performed V2-alternate skating without poles at moderate, high, and maximal speeds, both with free (SWING) and restricted arm swing (NOSWING). Maximal speed was 5% greater in SWING (P<0.01), while neuromuscular activation and produced forces did not differ between techniques. At both moderate and high speed the maximal (2% and 5%, respectively) and average (both 5%) vertical force and associated impulse (10% and 14%) were greater with SWING (all P<0.05). At high speed range of motion and angular …

Arm swing during skating at different skiing speeds affects skiing mechanics and performance

Effects of Aerodynamic Drag and Drafting on Propulsive Force and Oxygen Consumption in Double Poling Cross-country Skiing

Purpose To investigate the effects of aerodynamic drag and drafting on propulsive force (FPROP), drag area (CDA), oxygen cost (V˙O2), metabolic rate (E˙) and heart rate (HR) during roller skiing on a treadmill in a wind tunnel using the double poling technique. A secondary aim was to investigate the effects of wind versus no-wind test conditions on the same physiological parameters. Methods 10 subjects of each gender participated in the experiments. One pair of skiers of the same gender roller skied simultaneously in line with the air flow; the distance between the skiers was ~2.05 m. Each pair was tested as follows: I) with wind, leading; II) with wind, drafting; III) without wind. The tre…

A new testing device for the role of the trunk in force production and in balance control in disabled sitting athletes

In cross-country sit-skiing all athletes compete in a sitting position, but some of them have the ability to control their trunk more than others. The trunk plays an essential role in two performance determinants: propulsion generation and balance maintenance. The aim of the study is to design a new testing device assessing athletes’ responses to these propulsion determinants. The new device was composed of a seat surrounded by a sensorized aluminum frame. To assess propulsion generation, two force sensors were mounted in the anterior and posterior side of the frame, while two force sensors were embedded in two ropes elongated from the top of the frame. To measure trunk control, the device …

Comparison of Exclusive Double Poling to Classic Techniques of Cross-country Skiing

Introduction: This study aimed to 1) determine basic physiological demands during a simulated on-snow cross-country skiing (XCS) race when using grip-waxed skis (all classic XCS techniques [CLASSIC]), versus glide-waxed skis for exclusive double poling (DP) and 2) analyze in which track sections DP is different from CLASSIC under controlled gliding conditions in elite junior and senior skiers. Methods: Nineteen male and female elite XC skiers performed 1) two randomized simulated XCS races over 5.3 km using DP or CLASSIC measuring section times, V˙ O2, HR, blood lactate, and RPE; and 2) V˙ O2peak tests using diagonal stride and DP on treadmill. Results: The total group showed no differences…

Forward acceleration of the centre of mass during ski skating calculated from force and motion capture data

The purpose of this paper was to present and evaluate a methodology to determine the contribution of bilateral leg and pole thrusts to forward acceleration of the centre of mass (COM) of cross-country skiers from multi-dimensional ground reaction forces and motion capture data. Nine highly skilled cross-country (XC) skiers performed leg skating and V2-alternate skating (V2A) under constant environmental conditions on snow, while ground reaction forces measured from ski bindings and poles and 3D motion with high-speed cameras were captured. COM acceleration determined from 3D motion analyses served as a reference and was compared to the results of the proposed methodology. The obtained value…

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 de…

Contribution of sport science to performance: Nordic skiing

Balance Perturbations as a Measurement Tool for Trunk Impairment in Cross-Country Sit Skiing

In cross-country sit-skiing, the trunk plays a crucial role in propulsion generation and balance maintenance. Trunk stability is evaluated by automatic responses to unpredictable perturbations; however, electromyography is challenging. The aim of this study was to identify a measure to group sit-skiers according to their ability to control the trunk. Seated in their competitive sit-ski, 10 male and 5 female Paralympic sit-skiers received 6 forward and 6 backward unpredictable perturbations in random order. k-means clustered trunk position at rest, delay to invert the trunk motion, and trunk range of motion significantly into 2 groups. In conclusion, unpredictable perturbations might quantif…

Effects of Gliding Properties of Cross-Country Skis on the Force Production during Skating Technique in Elite Cross-Country Skiers

The aim of the present study was to examine how different gliding conditions of skis affect performance, cycle characteristics and leg and pole force production during V2 skating. Ten elite skiers skied on 100 m uphill (4°) at three different constant speeds (4.0, 4.8 and 5.6 m/s) and maximum speed using two differently prepared skating skis (fast and slow ski). With the slow ski, maximum speed was 6.4 % slower than with the fast ski. With constant speeds, cycle time got shorter due to a decrease in the recovery time of the leg and pole. Peak pole force and average cycle force increased as well as lateral leg forces while there were no changes in the vertical leg forces. A strategy for how…

Evaluating objective measures of impairment to trunk strength and control for cross-country sit skiing

AbstractIn Paralympic cross-country sit skiing, athlete classification is performed by an expert panel, so it may be affected by subjectivity. An evidence-based classification is required, in which objective measures of impairment must be identified. The purposes of this study were: (i) to evaluate the reliability of 5 trunk strength measures and 18 trunk control measures developed for the purposes of classification; (ii) to rank the objective measures, according to the largest effects on performance. Using a new testing device, 14 elite sit-skiers performed two upright seated press tests and one simulated poling test to evaluate trunk strength. They were also subjected to unpredictable bal…

Technical determinants of biathlon standing shooting performance before and after race simulation

The aim of this study was to identify performance- determining factors in biathlon standing shooting in rest and after intense exercise. Eight Finnish national- and nine junior- team biathletes participated in the study. Participants fired 40 resting shots (REST) and 2 × 5 competition simulation shots (LOAD) after 5 minutes of roller skiing at 95% of peak heart rate. Hit percentage, aiming point trajectory and postural balance were measured from each shot. Cleanness of triggering (ATV, movement of the aiming point 0- 0.2 second before the shot) and vertical stability of hold (DevY) were the most important components affecting shooting performance both in REST (DevY, R = −0.61, P < .01; ATV,…

Changes in biomechanics of skiing at maximal velocity caused by simulated 20 km skiing race using V2 skating technique

This study investigated how the fatigue caused by a 20 km simulated skating cross-country skiing race on snow affects the final spurt performance from a biomechanical perspective. Subjects performed a 100 meter maximal skiing trial before and at the end of the simulated race. Cycle characteristics, ground reaction forces from skis and poles, and muscle activity from eight muscles were recorded during each trial. Results showed that subjects were in a fatigued state after the simulated race manifested by 11.6% lower skiing speed (P < 0.01). The lower skiing speed was related to an 8.0% decrease in cycle rate (P < 0.01) whereas cycle length was slightly decreased (tendency). In temporal patte…

Measurement of Head Motion during Double-Poling Technique in Cross-Country Ski Classical Race using Kinematic GNSS

The Development and Precision of a Custom-Made Skitester

In the sport of cross-country skiing, equipment has a direct influence on results. Ski teams do extensive testing of different ski base grinds and products on a yearly basis. To achieve reliable results, the quality of methods used for testing skis needs to be taken in to account in addition to factors including the physical characteristics of testing personnel and changes in weather conditions. The aim of this study was to introduce a custom-made skitester, that was developed for testing skis on real snow, in laboratory conditions, and to evaluate its precision. The current skitester is capable of glide testing both classic and skate skis as well as kick simulation for the testing of grip …

Validation of portable 2D force binding systems for cross-country skiing

The aim of the present study was to design, construct and scientifically validate a two-dimensional force measurement binding system for cross-country skiing. The system consists of two force measurement bindings. One binding was designed for analysing classic skiing (vertical and anterior–posterior [along the ski] force components) and the other one for skate (freestyle) skiing (vertical and medio-lateral [transverse to the ski] force components). Validation was accomplished using a three-step process: (1) accuracy tests for the sensors in two temperatures, (2) sport-specific imitation jump test on standard force plates in a laboratory and (3) comparing the system against force measurement…

Sensors / Cross-country skiing analysis and ski technique detection by high-precision kinematic global navigation satellite system

Cross-country skiing (XCS) embraces a broad variety of techniques applied like a gear system according to external conditions, slope topography, and skier-related factors. The continuous detection of applied skiing techniques and cycle characteristics by application of unobtrusive sensor technology can provide useful information to enhance the quality of training and competition. (1) Background: We evaluated the possibility of using a high-precision kinematic global navigation satellite system (GNSS) to detect cross-country skiing classical style technique. (2) Methods: A world-class male XC skier was analyzed during a classical style 5.3-km time trial recorded with a high-precision kinemat…

Simulated skiing as a measurement tool for performance in cross-country sit-skiing

The International Paralympic Committee mandates the development of an evidence-based classification system, which requires a measure of performance. Performance in cross-country sit-skiing is mainly dependent on force generated during the poling phase and is enhanced by trunk flexion–extension movements. Since all sit-skiers have neuromuscular impairment, but different ability to control the trunk, this study aimed to verify if simulated action of poling on an adapted ergometer, together with a cluster analysis, could be used for grouping participants with different impairments according to their performance. On the ergometer, eight male and five female participants performed seven poling c…