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  • 1.
    Lund Ohlsson, Marie
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Danvind, Jonas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Technology and Management, Mechanical Engineering and Mathematics.
    Holmberg, L. Joakim
    Linköpings Universitet.
    Descriptive comparison of three technique analysis methods in the context of cross-country sit-skiing: energy expenditure and gross efficiency, descriptive biomechanics and musculoskeletal simulationsManuscript (preprint) (Other academic)
    Abstract [en]

    In parasports, technique analysis on how impairments and equipment affects athletic performance is important for classification. The purpose of this study was to compare three quantitative technique analysis methods: energy expenditure and gross efficiency, descriptive biomechanics, and musculoskeletal simulations for two cross-country sit-skiing sitting positions. These are: 1) knees higher than hips (KH) and 2) knees lower than hips with a frontal trunk support (KL).Five able-bodied cross-country skiers performed a sub-maximal incremental test and a 3 min maximal time-trial in each sitting position. During the tests, respiration, blood lactate concentrations, 3D full-body kinematics, pole forces and electromyography were measured.All three methods complement each other and by different parameters they all indicate superior technique in KH. Descriptive biomechanics showed differences in movement pattern, larger hip and spine flexion in KH. The method of energy expenditure and gross-efficiency capture both physiology and technique, showing lower anaerobic metabolism in KH. The musculoskeletal simulations showed how different muscle groups contributed to performance, showing higher contribution from spine and less in arms for KH. This study indicated why and how performance was enhanced in the human-equipment interaction, which is important for parasport classification and competition rules.

  • 2.
    Lund Ohlsson, Marie
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Danvind, Jonas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Technology and Management, Mechanical Engineering and Mathematics. Swedish Parasport Federation.
    Holmberg, L. Joakim
    Linköping University.
    LUMBAR SPINE REACTION FORCES IN SEATED PARA-SPORT: CROSS-COUNTRY SIT-SKIING2017In: Brisbane 2017: Abstract book, 2017Conference paper (Refereed)
    Abstract [en]

    INTRODUCTION

    For wheel-chair users shoulder injuries [1] and lower back injuries [2] are common. Lower back kyphosis of the spine, increases the anterior shear force in the lower back [3] and increases the risk of shoulder injuries [4].

     

    Cross-country sit-skiing (CCSS) is an endurance sport where the athlete is seated in a sledge mounted on a pair of skis and propel themselves by poling with a pair of sticks. This sport creates more equal loading on the muscles around the shoulder than wheel-chair rolling [5] which is positive in an injury perspective for the gleno-humeral joint [1].

     

    Athletes in CCSS with reduced trunk muscle control often sits in a sledge with their knees higher than their hips (KH) and a backrest. This position is hypothesized to be associated with spinal kyphosis and hence an increased risk of injuries. Therefore we have created a new sitting position with knees lower than hips (KL) with the trunk restrained on a frontal support.

     

    The aim of this study was to compute the L4/L5 joint reactions and compare the results between the positions KH and KL.

    METHODS

    Five female abled-bodied cross-country skiing athletes (62.6 ± 8.1kg, 1.67 ± 0.05m)  performed one exercise test session in each sitting position; The sessions included a sub-maximal incremental test, including 4-6 exercise levels of 3 min (exercise intensity nr 4, 37W, reflected race-pace) and a maximal time-trial (MAX) of 3 min on a commercial skiing ergometer (ThoraxTrainer A/S, Denmark).

     

    Full-body kinematics (Qualisys AB, Sweden) and pole forces (Biovision, Germany) were measured in 200 Hz. These data served as input to inverse dynamic simulations in The AnyBody Modelling system (AMS 6.0, Anybody Technology A/S, Denmark). For each participant and sitting position, simulations were made for exercise intensity 37W and MAX over four poling cycles using a 5th order polynomial muscle recruitment criteria. Compression forces and anterior shear forces between L4 and L5 were computed and normalized to each participant’s standing joint reactions. Data were compared pair-wise between the two sitting positions.

     

    Statistical significance (p ≤ 0.05) were marked with asterisk (*). Tendency of difference (0.05 ≤ p < 0.10) were marked (ǂ).

     

    RESULTS AND DISCUSSION

    Performance was higher in position KH (KL: 0.77±0.08 W/kg, KH: 1.00±0.14 W/kg, p < 0.01). No difference were observed in cycle length or cycle time. Kinematics results showed that KL had less spine flexion and range of motion in flexion. KH showed higher mean pole force in 37W and tendency of higher peak pole force in MAX.

     

    In standing, L4/L5 compression and anterior shear forces were 354 ± 45N and 32 ± 11N respectively. The normalized L4/L5 reaction forces (fig. 1) were larger in KH, especially during MAX intensity due to higher power. For equal power output, 37W, the mean anterior shear force was larger in KH and the mean compression force showed tendency of larger in KH (p=0.077).

     

    Figure 1: Normalized joint reaction forces, compression and anterior shear forces, between vertebrae L4/L5 for the two sitting positions KH and KL with trunk restraint. Min – minimal force, Maximal force and Mean – mean force over the four poling cycles.

     

    CONCLUSIONS

    Based on inverse-dynamics musculo-skeletal simulations of 5 abled-bodied athletes, the sitting position KL with frontal restraint reduced the compression and shear force between the L4/L5 vertebrae but impeded performance. This study shows the difficulty of comparing performance and safety in the same piece of equipment.

     

    ACKNOWLEDGEMENTS

    The authors acknowledge the Rolf & Gunilla Enström foundation and the Promobilia foundation, Sweden, for financial support, and the Ableway AB (Sweden) for construction of the sledges.

     

    REFERENCES

    1. Burnham RS, et al., Am J Sports Med, 21: 238-242, 1993.
    2. Thyberg M, et al., Disabil rehabil. 23:677-682, 2001.
    3. McGill SM, et al., Clin Biomech, 15: 777-780, 2000.
    4. Samuelsson KA, et al., J Rehabil Res Dev, 41: 65-74, 2004.
    5. Bjerkefors A, et al., Int J Sports Med, 34: 176-182, 2013.
  • 3.
    Lund Ohlsson, Marie
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Danvind, Jonas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Technology and Management, Mechanical Engineering and Mathematics.
    Holmberg, L. Joakim
    Linköpings Universitet.
    Shoulder and Lower Back Joint Reaction Forces in Seated Double Poling2018In: Journal of Applied Biomechanics, ISSN 1065-8483, E-ISSN 1543-2688, Vol. 34, no 5, p. 369-376Article in journal (Refereed)
    Abstract [en]

    Overuse injuries in the shoulders and lower back are hypothesized to be common in cross-country sit-skiing. Athletes with reduced trunk muscle control mainly sit with the knees higher than the hips (KH). To reduce spinal flexion, a position with the knees below the hips (KL) was enabled for these athletes using a frontal trunk support. The aim of the study was to compare the shoulder joint (glenohumeral joint) and L4-L5 joint reactions of the KL and KH sitting positions. Five able-bodied female athletes performed submaximal and maximal exercise tests in the sitting positions KL and KH on a ski ergometer. Measured pole forces and 3-dimensional kinematics served as input for inverse-dynamics simulations to compute the muscle forces and joint reactions in the shoulder and L4-L5 joint. This was the first musculoskeletal simulation study of seated double poling. The results showed that the KH position was favorable for higher performance and decreased values of the shoulder joint reactions for female able-bodied athletes with full trunk control. The KL position was favorable for lower L4-L5 joint reactions and might therefore reduce the risk of lower back injuries. These results indicate that it is hard to optimize both performance and safety in the same sit-ski.

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