Olli Ohtonen

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 skiers adapt on slower conditions was found. Skiers increased pole and lateral leg forces with slower speeds and with faster speeds, skiers increased the skiing frequency.

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 velocity of knee flexion were 24% greater with SWING (both P<0.05), while average EMG of m. biceps femoris was 31% lower (all P<0.05) in SWING. In a similar manner, the average EMG of m. vastus medialis and m. biceps femoris were lower (17% and 32%, P<0.05) during the following knee extension. Thus, swinging the arms while performing V2-alternate can enhance both maximal speed and skiing economy at moderate and, in particularly, high speeds.

Biomechanical analysis of different starting strategies utilized during cross-country skiing starts

Abstract The present study was designed to analyse and compare the kinetics and kinematics associated with three different starting strategies during classic cross-country ski racing. Inside a ski tunnel, 12 elite male skiers performed three sets of three 38 m starts. Each set included one start using: double poling only (DP), diagonal stride only (DIA) and freely chosen (FREE) (i.e. where subjects used the strategy or combination of strategies they felt was fastest) in random order. The first 18 m was performed on a series of force plates that measured horizontal and vertical forces followed by 20 m of a standard snow track. Additionally, cycle characteristics and joint angles were measured. DIA and FREE were faster over 38 m than DP (P < .01). Net horizontal impulse (taking into account both positive and negative impulses) 5–10 m after the start was lower during DP than during DIA and FREE (both P < .05). All subjects skied faster when using only DIA for the entire 38 m. Furthermore, the sum duration and frequency of propulsive contacts over the first 18 m was less in DP than DIA and FREE (P < .01). In conclusion, differences between the starting strategies examined was especially pronounced during the initial cycles. Transition from DIA to DP during the start also slowed the skiers, but optimal timing for such a transition was not elucidated.

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 legs while legs were emphasized with faster speeds. Higher forces were partly generated with greater vertical movement of the body, which might have elicited stretch-shortening cycle type of movement leading to greater force output.

A SIMPLE MULTIBODY DYNAMIC MODEL OF CROSS-COUNTRY SKI-SKATING

The purpose of this paper is to present the development of a simple multibody dynamic model matching the observed movements of the center of mass of a skier performing the skating technique in cross-country skiing. The formulation of the equation of motion was made using the Euler–Lagrange equations applied to a multibody tree-type system in three dimensions. The description of the lower limb of the skier and the ski was completed by employing three bodies, one representing the ski, and two representing the natural movements of the leg of the skier. This simple model is able to show an approximation of the movement of the center of mass of the skier and its velocity behavior allowing to study the effect of the key parameters used to build the model.Copyright

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

Arm swing has been shown to lead to greater maximal speed and movement economy in cross‐country skiing. The current study aimed to investigate how arm swing alters skiing mechanics and contributes to performance and acceleration of the athletes centre of mass (COM). While skiing on snow, seven highly skilled cross‐country skiers simulated V2‐alternate skating without using ski poles and with double or single arm swing and without arm swing. During leg push‐off the linear momentum of the body increased due to arm swing. Simultaneously, linear momentum of the arm(s) decreased in arm swing trials, indicating a transfer of momentum from arms to the rest of the body and being more prevalent with double arm swing compared to single arm swing (all P < 0.05). Greater maximal skiing speeds were reached with single and double arm swing, while the forward lean angle, the force leading to acceleration of COM in skiing direction, and the force effectiveness increased (all P < 0.05). The effects of less mass moving in single arm swing could be compensated by carrying out the arm swing faster, almost aligned in skiing direction and with a “long arm” pattern, indicating how arm swing can be conducted efficiently.

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‐m 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<.01). The lower skiing speed was related to an 8.0% decrease in cycle rate (P<.01), whereas cycle length was slightly decreased (tendency). In temporal patterns, relative kick time was increased (10.9%, P<.01) while relative poling time was slightly decreased (tendency). Vertical ski force production decreased by 8.3% while pole force production decreased by 26.0% (both, P<.01). Muscle activation was generally decreased in upper (39.2%) and lower body (30.7%) (both, P<.01). Together these findings show different responses to fatigue in the upper and lower body. In ski forces, fatigue was observed via longer force production times while force production levels decreased only slightly. Pole forces showed equal force production times in the fatigued state while force production level decreased threefold compared to the ski forces.