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  • Public defence: 2018-03-02 11:00 Q221, Östersund
    Lund Ohlsson, Marie
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Double Poling Incross-Country Skiing: Biomechanical and Physiological Analysis of Sitting and Standing Positions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Double poling (DP) is a sub-technique in cross-country skiing that has increased in interest over the last decades, e.g. athletes in cross-country skiing have increased their utilisation of double poling during competitions. In cross-country sit-skiing athletes with impairments in legs and/or trunk sit in a sledge and utilise DP to propel themselves. Technique (i.e. movement pattern) is one key factor determining performance but also a factor that may affect the risk of overuse injuries in sports.

    Therefore, the overall aim of the thesis was to improve the understanding of the human movement technique in cross-country skiing DP, in both standing (paper I-II) and sitting positions (paper III-IV, Thesis A-B) using biomechanical and physiological measurements and inverse dynamics simulations. All studies were carried out on a double poling ergometer in laboratory. Three experimental studies were performed with able-bodied participants (papers I-II, IV-VI), one study with one participant with growth defect in the legs (paper III), and one study (Thesis B) with one participant with complete spinal cord injury at thoracic vertebra 4.

    In paper I the first full-body simulation of DP was performed and results were comparable to results found in literature when the kinematics and external kinetics were similar. Paper II showed how increased leg utilisation increased performance (forward impulse) but reduced skiing efficiency (output work divided by metabolic muscle work). These results indicate that both high performance (power output) and efficiency may not be achieved in the same technique.

    In sitting DP many different sitting positions are utilised. Athletes with full muscle control in hip and trunk mainly sit with their knees lower than their hips (KLnoS). Athletes with paralysis in lower trunk and legs need trunk stability from the sit-ski. Most often, this is achieved by adopting a knees higher than hips (KH) position together with a support for the lower back. However, this position might induce large flexion in the spine, which is hypothesised to affect injury risk in the shoulders and lower back. This thesis has enabled the knees low sitting position for athletes with paralysis in the lower trunk and legs by supporting the anterior trunk with the sledge (KL).


    In sitting DP in athletes with full hip and trunk muscle control, high performance was achieved through proximal-distal sequencing from the hips through the trunk to the arms, and large muscle work in spine and legs (IV, V, Thesis A). In order of performance, KLnoS utilised muscles in the hips-spine-arms, compared with utilisation of spine-arms in KH, and mainly arms in KL. Higher amount of activated muscle mass resulted in lower relative anaerobic metabolism during submaximal exercise (IV).

    The lower back joint reactions were higher for the sitting position with larger spinal flexion, KH compared to KL (VI). These results suggest that there is an increased risk of injury in the lower back for the sitting position KH. Athletes with paraplegia generally have a high risk of injuries in the shoulders. The results of this thesis showed higher shoulder joint reactions in the sitting position with larger shoulder-arm muscle work, in KL compared to KH.

    For the case study with one participant with thoracic spinal cord injury (Thesis B) highest performance was achieved in the KH sitting position where spinal flexion occurred at the beginning of the poling phase. When comparing the fixed trunk positions KL and KHS, higher performance was achieved in KHS. It was speculated that the difference between KL and KHS was due to the impairment of the vasoconstriction in paralysed muscles. The effect of gravity on venous pooling is probably larger when the legs are lower down as in KL. This effect was not present for individuals without paralysis (III), where KL was more economical than KHS.

    Parasport classification needs evidence of how impairment affects sporting performance (Tweedy et al., 2014, Tweedy and Vanlandewijck, 2011). Classification might benefit from simulations as performed in this thesis. The musculoskeletal simulations of seated DP in paper V and the KLnoS position presented in the thesis have showed the relative contribution of different muscle groups on performance. These results are novel and might contribute to improvement of the classification system.

  • Public defence: 2018-04-06 10:15 F 234, Östersund
    Löfstrand, Pär
    Mid Sweden University, Faculty of Human Sciences, Department of Psychology.
    Communicating, Negotiating and Stereotyping: The roles of context, situation and gender in small group decision-making2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Making decisions together in groups takes an important role in society. Everywhere and in many different contexts people meet to make more or less formal decisions. As stereotypes constitute simplified group based perceptions of other people, decision-making groups risk making biased judgments and commit discriminating decisions. Stereotyping often follow the two universal dimensions competence and warmth (Cuddy, Fiske & Glick, 2008). How people´s judgments are affected by stereotypes has mainly been studied on individual level and less is known about how stereotypes and prejudice is communicated and negotiated in group decision-making situations. One approach to study this is to investigate how different contexts may lead to different communication patterns, different experiences, and different decisions.  In this thesis context was varied in two different ways in two experiments. In the first experiment the goal set for the decision-making was varied. A competitive goal was contrasted to a cooperative goal in a group decision task using a sports scenario where the participants had to select members to a relay team. In the second experiment different information was used as a context variable. This was done by varying the information of gender and parenthood status of the applicants in a fictive recruitment scenario. In addition, in both experiments the gender composition in the groups was varied, forming yet another variable that might play a role for how the decision-making was carried out. These three factors were assumed to influence the form of the communication, the content of the communication in terms of stereotyping, and how the decision-making process was experienced. A mixed-method approach was chosen where quantitative and qualitative data were used in conjunction with each other, which was assumed to give a richer picture of the results.

    In paper I the form of the communication, as analyzed with interaction process analysis (IPA), did not differ much between the two goals. On the other hand, the content showed more systematic patterns. A competitive goal seemed to lead to both inclusion and exclusion with use of both positive and negative stereotypes. A cooperative goal seemed to lead to inclusion mechanisms and only use of positive stereotypes. In paper II where the aim was to investigate what was experienced as constituting a successful decision-making process it was found that equality of influence was of importance. Furthermore, qualitative analyses of the conversation patterns, by use of the conversational argument coding scheme (CACS), seemed to validate this. The successful groups had a more complex communication pattern than the less successful groups. In paper III, where the information for the decision task was varied in terms of gender and parenthood status of the applicants, it was found that parenthood information triggered a lot of discussion. The participants did not differentiate between mothers and fathers, but they applied attributes of competence and warmth differently to the targets. Furthermore, gender and gender composition seemed to matter as male and female groups applied the attributes differently. Paper IV used data from both experiments in order to investigate how the context variables and gender composition influenced how the decision situation was experienced. The results indicate that the context variables and gender composition interacted with own gender. Men seemed more content in male groups with male targets and a male parent condition while women seemed more content in mixed groups and a female parent condition.

    Context seems to play an important role, as it provides the participants in the group discussions with different information, leading to different patterns of stereotyping in the discussions. Also how the decision was experienced seems to be related to the context. Furthermore, group composition seems to function in this way too. The results are discussed in relation to practical implications and suggestions for future research.