Michael Buchecker

Several methodologies have been proposed to determine turn switches in alpine skiing. A recent study using inertial measurement units (IMU) was able to accurately detect turn switch points in controlled lab conditions. However, this method has yet to be validated during actual skiing in the field. The aim of this study was to further develop and validate this methodology to accurately detect turns in the field, where factors such as slope conditions, velocity, turn length, and turn style can influence the recorded data. A secondary aim was to identify runs. Different turn styles were performed (carving long, short, drifted, and snowplow turns) and the performance of the turn detection algorithm was assessed using the ratio, precision, and recall. Short carved turns showed values of 0.996 and 0.996, carving long 1.007 and 0.993, drifted 0.833 and 1.000 and snowplow 0.538 and 0.839 for ratio and precision, respectively. The results indicated that the improved system was valid and accurate for detecting runs and carved turns. However, for drifted turns, while all the turns detected were real, some real turns were missing. Further development needs to be done to include snowplow skiing.

In order to gain insight into skiing performance, it is necessary to determine the point where each turn begins. Recent developments in sensor technology have made it possible to develop simpler automatic turn detection methodologies, however they are not feasible for regular use. The aim of this study was to develop a sensor set up and an algorithm to precisely detect turns during alpine ski, which is feasible for a daily use. An IMU was attached to the posterior upper cuff of each ski boot. Turn movements were reproduced on a ski-ergometer at different turn durations and slopes. Algorithms were developed to analyze vertical, medio-lateral, anterior-posterior axes, and resultant accelerometer and gyroscope signals. Raw signals, and signals filtered with 3, 6, 9, and 12 Hz cut-offs were used to identify turn switch points. Video recordings were assessed to establish a reference turn-switch and precision (mean bias = 5.2, LoA = 51.4 ms). Precision was adjusted based on reference and the best signals were selected. The z-axis and resultant gyroscope signals, filtered at 3Hz are the most precise signals (0.056 and 0.063 s, respectively) to automatically detect turn switches during alpine skiing using this simple system.

This study evaluated the amount, and particularly, the structure of variability in postural control accompanying an unstable shoe (US) application. Mediolateral and anterior–posterior center of pressure signals plus electromyographic profiles of the tibialis anterior and gastrocnemius medialis were recorded in 29 asymptomatic men while wearing both US and flat shoes. Statistical analysis included common measures of dispersion as well as sample entropy and largest Lyapunov exponent estimates. Data were compared by two-way repeated-measures analysis of variance. Corresponding main effects of footwear revealed that, in contrast to the flat shoes condition, the US intervention consistently increased center of pressure and electromyographic net fluctuations and rendered the overall system less complex, as reflected by the lower sample entropy and higher Lyapunov exponent values observed throughout. Accordingly, employing US in stance should be functional concerning motor development; however, the greater sensi...

Purpose:: To identify biomechanical predictors that distinguish between high- and low-score athletes in biathlon shooting and to determine the relationships among these variables in field testing.Methods:: Twenty-two biathletes (8 female, 14 male) from the World Cup, the European Cup, and a federal youth squad each fired 3 clips of 5 shots in prone and standing shooting positions without physical load, followed by 2 respective series in both disciplines during a simulated 12.5-km pursuit race on roller skis. Biomechanical variables describing triggering, rifle force in the back shoulder, and body and rifle sway were calculated over the last 0.5 second before firing. For computed linear discriminant analyses, subjects were divided into high- and low-level performers based on mean scores for each condition separately. In addition, correlations among all biomechanical factors were calculated.Results:: Regarding prone shooting, shoulder force in the rest condition and vertical rifle sway in the race simulation were shown to be main discriminators. Several body- and rifle-sway variables were found to be predictors in standing rest shooting. Body sway across the shooting line discriminated the groups in the standing race situation tendentially. Thus, the main performance predictors changed due to fatigue. Correlations between triggering and rifle sway, shoulder force and rifle sway, and body sway and rifle sway were discovered.Conclusions:: Referring to the current results, athletes are recommended to focus on vertical rifle sway in prone position and on body sway across the shooting line during standing shooting when fatigued.

Es compared with slower individuals. Furthermore, the importance of the so-called “front side mechanics” for elite sprint performance is frequently emphasized by researchers and coaches. Recently, it was demonstrated that using a body-weight supporting kite during full-effort sprints in highly trained sprinters leads to a reduction in ground contact time. The aim of this study was to investigate possible negative effects of this body-weight supporting device on sprint running kinematics, which was not clarified in previous studies. Eleven well-trained Austrian sprinters performed flying 20-m sprints under 2 conditions: (a) free sprint (FS); and (b) body-weight supported sprint (BWS). Sprint cycle characteristics were recorded during the high-speed phase by a 16 camera 3D-system (Vicon), an optical acquisition system (Optojump-next), and a high-speed camera. Paired sample t-tests and Cohen's d effect size were used to determine differences between sprinting conditions. Compared with FS, BWS caused a decrease in ground contact time by 5.6% and an increase in air time by 5.5% (both p < 0.001), whereas stride length and rate remained unchanged. Furthermore, a reduced hip joint extension at and after take-off, an increased maximal hip joint flexion (i.e., high knee position), and a smaller horizontal distance of the touchdown to the center of gravity could be observed (all p < 0.01). These results indicate no negative effects on front side mechanics during BWS and that sprinting with a body-weight supporting kite seems to be a highly specific method to reduce ground contact time in well-trained sprinters....

This study investigated the effect of a 12‐week recreational skiing intervention on lower limb muscle strength and cardiorespiratory fitness in participants with unilateral total knee arthroplasty (TKA). Twenty‐seven older adults (70 ± 5 years) were assigned to the intervention (n = 13) or control group (n = 14) after surgery (2.5 ± 1 years). Leg muscle strength was measured using an IsoMed 2000 dynamometer and cardiorespiratory fitness was determined by cycle ergometry before and after the intervention as well as after an 8‐week retention period. The skiing intervention led to increased muscle strength in the operated leg during unilateral single joint isometric extension (maximal force: 11%; P < 0.05; rate of torque development: 24%; P < 0.05) and during the unilateral multi‐joint isokinetic single leg strength test (8%; P < 0.05). This resulted in a decreased asymmetry index in the isokinetic test (13% to 5%; P < 0.05). These adaptations remained unchanged toward the retention test. No effect was observed for cardiorespiratory fitness. The results demonstrate that muscle contraction forces required during recreational skiing in individuals with TKA seem adequate and effective to increase quadriceps and hamstrings muscle strength in the initially weaker operated leg and to reduce an augmented post‐operative asymmetry index.

The aim of the study was to examine the effect of a 12‐week recreational skiing intervention on functional gait performance in people with unilateral total knee arthroplasty (TKA). Twenty‐three older adults (71 ± 5 years) were assigned to the intervention (IG) or control group (CG). Test time and ground reaction forces (GRF) were recorded at pre‐ and post‐intervention and in the retention phase during functional gait tests. Ground contact was recorded bilaterally and divided into the weight acceptance and push‐off phases. In IG, a faster stair descent time (16%) was observed at post‐test with no further change at the retention test. The asymmetry indices for all analyzed variables were decreased in stair descent and during weight acceptance in stair ascent and level walking without further changes between post‐ and retention test. The reduced asymmetries occurred mainly because of increased loading of the operated leg. Most variables were unchanged in CG. Similar to the force data, the asymmetry index for temporal stride characteristics was reduced in all stair descent variables. These results demonstrate that alpine skiing as a leisure‐time activity has a beneficial effect on gait performance and leads to a more balanced load distribution between the legs during daily activities.

The aim of the current study was to examine postural balance, rifle stability and shooting performance in biathletes, analysing the basic precision shooting skills without physical load in different performance groups. Therefore, kinematic and kinetic data from the World Cup (WC; n = 8), the European Cup (EC; n = 13) and a federal youth athletes' squad ( n = 15) were recorded on an indoor shooting range. The participants had to shoot ten 5-shot-clips without physical load. Postural balance and rifle stability were measured by VICON (Oxford, UK) and PEDAR (Munich, Germany) systems over the last 0.6 s before firing. WC and EC groups showed lower body and rifle sway (mainly in cross-shooting direction) compared to youth athletes (p < 0.05). Postural balance and gun stability predominantly in cross-shooting direction were negatively correlated to shooting performance ( r = −0.33 to −0.59; p < 0.05). The present data indicate the relevance of low body and rifle sway primarily in cross-shooting direction for a successful basic biathlon standing shooting at rest. Special biathlon specific balance and rifle stability training forms used in basic shooting trainings can be recommended.