Mid Sweden University

In snowboard freestyle, rotation is the key indicator of trick difficulty, encouraging riders to perform tricks with more rotation. In many cases, snowboarders learn and practice tricks using training tools such as trampolins and/or landingbags before they transfer this tricks on-snow. It has not yet been scientifically investigated which movement parameters are primarily responsible for the acquisistion of increasingly difficult cork tricks. Hence, the aim of this study was to investigate the influence of each theoretically defined performance parameter on the amount of rotation using deterministic models for halfpipe and kicker tricks, separated for the direction of rotation, performed on a trampoline with a bounce board. Kinematic motion tracking was used to determine biomechanical performance parameters of 157 corks performed by 15 riders, and random intercept models were used to develop deterministic models. The results show that regardless of the discipline and direction of rotation, angular velocity, take-off velocity and the moment of inertia are key performance indicators to increase the amount of rotation. The coefficient of determination showed a high goodness-of-fit and the standardized estimate was highly significant for all investigated performance parameters. These results are important for coaches and riders to teach and learn new skills.

Lateral ankle sprains are the most common injuries in indoor and court sports, with ankle inversion being a primary injury driver. Stabilising the ankle during multidirectional changes is crucial for injury prevention. Conversely, increased shoe stiffness has been hypothesised to influence the magnitude of ankle inversion and may raise the risk for ankle injuries. Therefore, the purpose of this study was to investigate the influence of shoe longitudinal bending stiffness on ankle biomechanics during indoor and court sport-specific cutting movements. Biomechanical data from 19 participants were collected using a motion capture system and force plate. A jump-cut protocol with two different cutting directions after landing was performed in indoor shoes with and without carbon plate inserts of varying stiffness. Ankle kinematics and kinetics were analysed with statistical parametric mapping and repeated measures analysis of variance. A significant increase in ankle inversion during the 180° cut and a reduction in forefoot inversion (foot torsion) for stiffer footwear conditions during both the 45° and 180° cut were observed. While dorsiflexion moments differed during the last 10% of ground contact, ankle inversion moments did not significantly diverge between shoe conditions. Furthermore, a noteworthy correlation between footwear longitudinal bending stiffness and torsional stiffness was identified. In conclusion, increased bending stiffness significantly affected ankle and foot kinematics. The ankle compensated for restricted mobility and higher demands during high-degree jump-cuts, while foot torsion played a more prominent role in low-degree cuts. The heightened ankle inversion during high-degree cuts may induce an elevated risk for lateral ankle sprains. Further longitudinal studies are necessary to comprehensively understand injury incidence and the role of shoe stiffness in injury prevention. 

In snowboard freestyle disciplines, the amount of rotation is commonly determined as the sum of rotations around all board axes and is the most important indicator of the trick difficulty across all snowboard freestyle disciplines. Based on the type of rotation, tricks can be classified as flatspins, corks and flips. It is not yet known whether the type of rotation of a trick can influence the actual amount of rotation. Therefore, the aim of this study was to determine the amount of deviation, defined as difference between measured and assumed amount of rotation as a function of trick classification, using kinematic motion analysis. The amount of deviation was positive for flatspins (median: 21 degrees; min: -4 degrees; max: 49 degrees) and negative for corks (median: -25 degrees; min: -89 degrees; max: 12 degrees) and flips (median: -28 degrees; min: -94 degrees; max: 13 degrees). Our results demonstrate that there are ways of execution where riders perform corks and flips with a shortcut and flatspins with a detour. This should be taken into account by judges, coaches and riders. Further research is needed to investigate how the shortcut can be influenced.

Several different sitting postures are used in Paralympic cross-country sit-skiing. The aim of this study was to evaluate the impact of sitting posture on physiological and mechanical variables during steady-state double-poling sit-skiing, as well as to determine how seat design can be improved for athletes without sufficient trunk control. Employing a novel, custom-designed seat, three trunk positions were tested while performing double-poling with submaximal oxygen consumption on an ergometer. Cycle kinematics, pole forces, and oxygen consumption were monitored. The athlete performed best, with longer cycle length and less pronounced metabolic responses, when kneeling with the trunk resting on a frontal support. For this case, a forward leaning trunk with knees below the hip joint was interpreted as most optimal, as it showed lower oxygen consumption and related parameters of performance during cross-country sit-skiing. Further investigations should examine whether such improvement is dependent on the level of the athlete’s handicap, as well as whether it is also seen on snow.

An effective start enhances an athlete's chances of success in ski cross competitions. Accordingly, this study was designed to investigate the biomechanics of start techniques used by elite athletes and assess the influence of different start environments. Seven elite ski cross athletes performed starts indoors on a custom-built ramp; six of these also performed starts on an outdoor slope. Horizontal and vertical forces were measured by force transducers located in the handles of the start gate and a 12-camera motion capture system allowed monitoring of the sagittal knee, hip, shoulder, and elbow kinematics. The starting movement involved Pre, Pull, and Push phases. Significant differences between body sides were observed for peak vertical and resultant forces, resultant impulse, and peak angular velocity of the shoulder joint. Significantly lower peak vertical forces (44N), higher resultant impulse (0.114Ns/kg), and knee joint range of motion (12 degrees) were observed indoors. Although movement in the ski cross start is generally symmetrical, asymmetric patterns of force were observed among the athletes. Two different movement strategies, i.e. pronounced hip extension or more accentuated elbow flexion, were utilised in the Pull phase. The patterns of force and movement during the indoor and outdoor starts were similar.

The mixed bowling action is associated with injuries in the lumbar spine and has been shown to have no performance benefits over other bowling actions. The purpose of this study was to assess the mixed bowling action with reference to a more comprehensive classification system to facilitate the development of more targeted bowling action remediation programs. A total of 70 fast bowlers were tested using a three-dimensional motion analysis system (240 Hz). Kinematic data of the shoulders and pelvis were analysed with respect to a modified set of angle threshold criteria to classify bowling actions. It was found that the mixed action bowlers (49% of the sample) could be sub-divided into seven distinct mixed action types. The most common of these types were the mixed front-on bowlers with respect to shoulder counter-rotation (19%) and the mixed front-on bowlers with respect to both pelvis-shoulder separation angle and shoulder counter-rotation (14%). It is envisaged that a more comprehensive classification of bowling actions may assist researchers in the future to define mixed action types with a tighter domain of variables that are more indicative of lumbar injury risk. © 2014 Taylor & Francis.

This study aimed to compare kinematic data collected during ski-cross starts outdoors on snow in daylight (high albedo) to similar data collected indoors with infiltrating sunlight but without light reflections from the snow (low albedo) using a video-based motion capture system with the active filtering function enabled. A 12-camera 3D motion capture system (Qualisys AB, Sweden) was used to measure test objects and eight skiers performing a ski-cross start on a slope outdoors and on a wooden start ramp indoors. The average residuals and standard deviations of the length of the calibration wand calculated indoors and outdoors by the calibration software were compared using descriptive statistics. Static and moving fixed length measures and thigh length measures were compared using Bland-Altman plots. Calibration residuals were slightly increased outdoors (1.77 mm) compared to indoors (1.54 mm), while wand length varied by 3.63 and 1.51 mm, respectively. Fixed static lengths differed by -8.65 ± 4.94 mm (shorter indoors), whereas fixed moving lengths differed by 0.85 ± 1.05 mm (longer indoors). A randomly chosen marker pair on one segment (Thigh) showed a mean difference of 1.19 ± 22.05 mm (longer indoors). It is concluded that 3D motion capture outdoors on snow in daylight is feasible, provides kinematic data comparable to indoors, and could be used to research biomechanics in snow sports.

The golf swing is a complex, multi-planar, three-dimensional (3D) motion sequence performed at very high speeds. These properties make biomechanical analysis of the golf swing difficult. Hence, the aim of this study was to develop a computer model of the golf swing capable of calculating a diverse range of 3D kinematics and kinetics values based on motion analysis data collected in the laboratory. Five golfers performed six swings in the field of view of eight Falcon High Speed Resolution cameras (240 Hz), which captured the movements of 56 markers placed on the golfers and their clubs, resulting in marker trajectories that were processed into linear xyz-coordinates using the Eva Motion Analysis system. To perform the kinematics and kinetics calculations, a 20-segment rigid body model of the human body was designed in the Mechanical Systems Pack, connecting the segments by a selection of linear and spherical constraints, resulting in a system of segments with 58 degrees of freedom, with the constraint equations of motion calculated by the Newton-Lagrangian iteration method. The model allowed for the derivation of segmental sequencing, separation angles, segmental planes of motion, segmental velocity contributions, joint torques and muscle powers. The preliminary data suggest that such an integrated kinematics and kinetics analysis is necessary to understand the mechanical complexity of golf swing. Even with the small sample size analysed in this study, some interesting trends were found, such as certain violations of the classical proximal-to-distal sequencing scheme, differing swing plane and club head trajectories in the backswing and downswing phases, minimal hip angular velocity contribution to the ball at impact, concentric and eccentric muscle powers in the downswing phase, and increased lumbar loading factors from the mid-downswing phase to ball impact. © 2014 Taylor & Francis.