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.

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) correlated well; (3) recovery time and time to peak did not differ and time to impact correlated with each other (r=0.88, p<0.01); (4) no differences were found in peak electromyography (EMG) and average EMG for Triceps, Pectoralis, and Erector Spinae; Rectus Abdominis did not differ in peak. EMG peak and average EMG of all muscles were correlated between the two conditions (r=0.65-0.94; p<0.05-0.01). Although some differences were observed, this study demonstrated that technical skill proficiency in natural and simulated cross-country skiing is comparable from a force production and muscle activation perspective.

Alpine Skiing With total knee ArthroPlasty (ASWAP): effects on strength and cardiorespiratory fitness.

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.

Alpine Skiing With total knee ArthroPlasty (ASWAP): effects on gait asymmetries.

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.

Alpine Skiing With total knee ArthroPlasty (ASWAP): symmetric loading during skiing.

The aim of this pilot study was to determine the pressure distribution, symmetry of load between operated (OP) and non-operated (NOP) leg, and pain level during alpine skiing in participants with unilateral total knee arthroplasty (TKA). The responses of the dependent variables were analyzed following a 10-week guided skiing intervention of 2-3 days of skiing per week. Ground reaction force (GRF) was recorded bilaterally and was determined for 13 participants with TKA (65 ± 4 years) at pre- and post-test. Additionally, pain perception was determined using a numeric rating scale in the OP leg at both test sessions and after each skiing day. No statistical differences were observed between OP and NOP legs for peak and average GRF as well as the asymmetry indices at pre-test. Pain perception was low and was not increased as a consequence of the skiing intervention. In conclusion, alpine skiing did not lead to increased or decreased loading of the OP leg compared with the NOP leg. Therefore, alpine skiing may be allowed for patients with skiing experience and a good clinical outcome.

Effects of age on lower extremity joint kinematics and kinetics during level walking with Masai barefoot technology shoes.

BACKGROUND: The age-associated loss of physical function engenders gait patterns which jeopardise the knee and hip to osteoarthritis. Masai Barefoot Technology (MBT) shoes have been shown to provide a facility to address specific needs for load modification in terms of musculoskeletal disease prevention in people with restricted proprioceptive or strength abilities. Therefore, a readjustment of lower extremity joint loading profiles in the elderly was hypothesised when using this type of footwear. AIM: The aim of this study was to evaluate the effects of MBT shoes on gait kinematics and kinetics in both an elderly and young cohort during walking. DESIGN: This was a cross-sectional study. SETTING: A 3-dimensional motion analysis laboratory. POPULATION: Eleven healthy elderly men and 11 healthy young men. METHODS: A conventional sport shoe served as control situation to MBT. Subjects were advised to walk eight trials per shoe at a criterion speed of 1.5 ± 0.1 m·s(-1) in block-randomised order. Peak joint angles, moments and powers at the ankle, knee and hip were calculated through an inverse dynamic model. Data were compared by a two-way repeated measure ANOVA (α=0.05). RESULTS: MBT reduced external ankle joint moments and powers independent of age. At the hip, MBT footwear led to decreases in external hip flexion moments and concentric hip power output during early and late stance. Herein, no age-by-condition effects were present. Moreover, MBT reduced external knee flexion moments and concentric knee extensor powers at loading response, with the greater changes observed in the elderly. Additionally, a main effect of condition showing a general decrease in the MBT situation, but no interaction effect was noted for first peak external knee adduction moments. CONCLUSION: These results suggest that MBT shoes diminish joint loads among age groups, whereas compared to young adults, the elderly, in particular, benefited from MBT footwear with regard to relief stress on the knee joint region. CLINICAL REHABILITATION IMPACT: Based on these findings, the use of MBT shoes may attenuate the risk of developing knee and hip osteoarthritis in the elderly and may play an important role regarding pain avoidance and/or disability.

Effect of instability training equipment on lower limb kinematics and muscle activity.

To improve the effectiveness of training or therapy, it is important to know the benefits for each type of instability training equipment. The aim of this study was to show differences in lower limb kinematics and muscle activation during single leg standing on a slackline (SL) compared to a multi-functional rocker board (MD) and an air cushion (AC). In 14 subjects, mean angular velocity of the hip, knee and ankle, as well as the muscle activity (iEMG) from six lower limb muscles were recorded during 12 s of single leg standing task. Ankle in-/eversion and knee ab-/adduction angular velocity were highest for SL followed by MD and AC (all p < 0.05), as well as in the hip flex-/extension angular velocity with higher values for SL compared with AC (p < 0.01). Regarding iEMG, the rectus femoris muscle showed higher values for SL compared with MD (p < 0.05) and AC (p < 0.01). iEMG of biceps femoris muscle demonstrated higher values for MD compared to AC (p < 0.05), but with no difference to SL. Balancing on a SL is a more challenging exercise for the postural control system compared to MD and AC, and affects the knee and hip joint motion in particular.

Analysis of a simulated sprint competition in classical cross country skiing.

The objectives of this project were first to analyze the physiological response of a classical cross country (XC) skiing sprint competition, second, to examine the relationships of kinematic and physiological variables with sprint performance and third, to test the hypothesis that maximal speed in double poling (DP) and diagonal stride (DIAG) predicts sprint performance. Twelve elite skiers performed a treadmill-based simulation of a sprint competition that included two maximal speed tests (DP, DIAG), a test and three sprint heats over a 3.5-h period. VO(2), lactate, heart rate (HR) and kinematic variables were measured. Maximal DP and DIAG speed, the level of repeatedly produced lactate values and skiing technical aspects positively correlated with sprint performance. Fastest skiers produced longer cycle lengths in all techniques at equal poling frequency. VO(2) variables showed no correlation to sprint performance. VO(2), tidal volume (VT), and lactate decreased over the heats. XC-sprint performance in classical style depends on speed abilities, technique use, fatigue resistance, and anaerobic capacity. The relationship of maximal speed with sprint performance suggests (a) integrating maximal speed tests in XC sprint diagnostics and (b) emphasizing training models for XC skiing-specific speed abilities to improve performance in XC skiing sprint.

Comparisons of the ski turn techniques of experienced and intermediate skiers.

We compared selected kinematic variables for four different ski turn techniques performed by five experienced and five intermediate male skiers. The four ski turn techniques were the upstem turn, the downstem turn, the parallel turn and the parallel step turn. Each turn was divided into the initiation phase and the first and second steering phases. Most of the statistically significant differences (P < 0.05) between the two groups were found for the initiation phases of the four turns. Both the hip axis-hand axis angle and the edging angle of the uphill ski were significantly different between the two groups for the upstem turn at the beginning of the initiation phase. For the downstem turn, significant differences between the groups were found at the start of the initiation phase for the hip axis-hand axis angle, the shoulder axis-fall line angle, and the edging angle of the uphill ski. The standard deviation of the distance between the tips of the two skis over the second steering phase also differed significantly between the two groups. For the parallel step turn, significant differences were found at the start of the initiation phase for the edging angle of the downhill ski and the downhill ski to movement direction angle. Significant differences were also found for the edging angle of the downhill ski in the middle of the second steering phase and the shoulder axis to movement direction angle at the end of this phase. For the initiation phase of the parallel turn, significant differences were found for the timing of setting the ski pole, the uphill knee angle at the start of this phase and the range of the knee angle of the uphill leg from the start to the end of this phase. For this turn, significant differences between the two groups were also found for the edging angle of the downhill ski in the middle of the second steering phase and the shoulder axis to movement direction angle at the end of this phase. One of the reasons it was possible to identify a few significant differences only for the turns analysed, was the variability within the intermediate group: for most of the variables analysed, the standard deviation was much higher for the intermediate than for the experienced group.