abstract: Humans moving in the environment must frequently change walking speed and direction to negotiate obstacles and maintain balance. Maneuverability and stability requirements account for a significant part of daily life. While constant-average-velocity (CAV) human locomotion in walking and running has been studied extensively unsteady locomotion has received far less attention. Although some studies have described the biomechanics and neurophysiology of maneuvers, the underlying mechanisms that humans employ to control unsteady running are still not clear. My dissertation research investigated some of the biomechanical and behavioral strategies used for stable unsteady locomotion. First, I studied the behavioral level control of human sagittal plane running. I tested whether humans could control running using strategies consistent with simple and independent control laws that have been successfully used to control monopod robots. I found that humans use strategies that are consistent with the distributed feedback control strategies used by bouncing robots. Humans changed leg force rather than stance duration to control center of mass (COM) height. Humans adjusted foot placement relative to a "neutral point" to change running speed increment between consecutive flight phases, i.e. a "pogo-stick" rather than a "unicycle" strategy was adopted to change running speed. Body pitch angle was correlated by hip moments if a proportional-derivative relationship with time lags corresponding to pre-programmed reaction (87 ± 19 ms) was assumed. To better understand the mechanisms of performing successful maneuvers, I studied the functions of joints in the lower extremities to control COM speed and height. I found that during stance, the hip functioned as a power generator to change speed. The ankle switched between roles as a damper and torsional spring to contributing both to speed and elevation changes. The knee facilitated both speed and elevation control by absorbing mechanical energy, although its contribution was less than hip or ankle. Finally, I studied human turning in the horizontal plane. I used a morphological perturbation (increased body rotational inertia) to elicit compensational strategies used to control sidestep cutting turns. Humans use changes to initial body angular speed and body pre-rotation to prevent changes in braking forces. / Dissertation/Thesis / Ph.D. Kinesiology 2012

Title: The influence of the strengthening of the lower extremities performance in 100 m breaststroke. Goals: The thesis aims to determine the effect of specific and non-specific exercises on the performance of the lower extremities in the 100 m breaststroke. Methods: To assess and verify the beginning, during and end of our investigation we have used these methods. Anthropometric indicators - age, height, weight, BMI (body mass index), foot length and length of lower extremities. Determining the maximal performance and number of strokes in the 100 m breaststroke. The level of explosive force of lower limbs by performing a vertical jump. And power endurance level of the lower extremities with the flexibility of the hip and knee joints by making deep squats to maximum. Results: The results of the work provide information on the impact of the strengthening of the lower extremities performance in the 100 m breaststroke. Based on the results was observed significance of these measurements using the Wilcoxon matched pairs test. For probands in the final measurements marked improvement. Key Words: breaststroke technique, strength, lower extremity, specific and non- specific exercises

Title: Developing the explosive strength of the lower extremities of the players of the extra league team in volleyball. Subject: Measuring the jump height of twelve players of the extra league team. Objectives: Measure to see if it is possible, by systematically training the explosive strength of the lower extremities, to increase the jump height for volleyball players after a period of three months. Results: To compare the results of each single measurement with the first measurement performed prior to systematic training of the explosive strength of the lower extremities Key words: Development, explosive strenght, lower extremities, player, volleyball, team.

The computational musculoskeletal models that are used to study muscle moment-generating capacities of persons with movement disorders and planning treatment options must be accurate, and take into account the inter-individual variability of musculoskeletal geometry. In Paper I the methods of creating the subject-specific musculoskeletal model of the lower extremities from magnetic resonance images (MRIs) were developed. The subject-specific model was used to analyze hip, knee and ankle muscle moment arms (MALs) and muscle-tendon lengths (MTLs) during gait in a subject with unilateral cerebral palsy (CP), and to evaluate the accuracy of widespread and commonly-used scaled generic model. It was found that the scaled generic model delivered accurate values for changes in MTLs in most muscles. However, the scaled generic and the subject-specific lower extremity musculoskeletal models showed substantial differences in MALs calculated during gait. In Paper II subject-specific musculoskeletal models of nine subjects with unilateral CP were created to study muscles volumes, MTLs and MALs; and to examine the accuracy of MALs calculated by the scaled generic models. It was shown that the scaled generic model significantly underestimated hip MALs discrepancies between the affected and the non-affected sides of the lower extremities. However, it significantly overestimated hip adduction/abduction of gluteus maximus, gluteus medius, gluteus minimus, tensor fascia latae and biceps femoris long head; and hip flexion of adductor longus and rectus femoris in the affected and the non-affected sides. It was also found that muscle volumes and hip abduction MALs in gluteus medius and gluteus minimus, hip flexion MALs in iliacus and hip rotation in gluteus maximus were smaller in the affected side of lower extremities. MTLs in the affected and the non-affected sides throughout the range of hip motion were similar. This thesis suggests the need for the subject-specific musculoskeletal models that can account for variability of muscle attachments and musculoskeletal geometry of persons with movement disorders. Based on inaccuracies of the scaled generic model reported here, the generic models that are used to guide treatment decisions must be tested, and interpreted with care. / QC 20110901

BACKGROUND: Previous studies have shown a high injury rate in the lower extremities among military recruits. A correlation has been shown between female gender or a low level of physical activity prior to basic military training and a higher risk of injury. AIM: To investigate the self-reported injury rate in the lower extremities among Swedish recruits and the difference in injury rate between men and women. Another aim was to investigate correlation between self-reported injury rate in the lower extremities and self-reported physical activity, and to study this correlation for both men and women. METHOD: A quantitative study with a prospective, descriptive, comparative and correlative design. Data from two different questionnaires were answered by 177 recruits. RESULTS: 26% of the recruits reported injury in lower extremities after completing the basic training. There was a significant difference (p=0.006) in self-reported injury between female and male recruits. The level of prior physical activity and the injury rate amongst the recruits had a low correlation. CONCLUSION: The results indicate a high injury rate among Swedish recruits, especially among the female recruits. No correlation between self-reported physical activity and the injury rate in lower extremities was found. / BAKGRUND: Tidigare studier visar på hög skadeprevalens i nedre extremiteter hos militära rekryter under grundläggande militär utbildning. Samband har setts mellan kvinnligt kön eller låg fysisk aktivitetsnivå före utbildningsstart och ökad skaderisk. SYFTE: Undersöka den självrapporterade skade-/besvärsprevalensen i nedre extremitet hos svenska rekryter efter avslutad grundläggande militär utbildning (GMU), samt studera skillnader mellan könen i detta avseende. Syftet var också att undersöka sambandet mellan självrapporterad fysisk aktivitetsnivå inför GMU och skade-/besvärsprevalensen i nedre extremiteter efter genomförd utbildning samt studera sambandet för män respektive kvinnor. METOD: En kvantitativ studie med prospektiv, deskriptiv, komparativ och korrelerande design. Data från två olika enkäter besvarades av 177 rekryter. RESULTAT: 26% av rekryterna rapporterade skada/besvär i nedre extremitet vid avslutad utbildning. Signifikant skillnad (p=0,006) kunde ses i självrapporterad skade-/besvärsprevalens mellan kvinnliga (42%) och manliga (21%) rekryter. Nivå av fysisk aktivitet och skade-/besvärsprevalensen hos rekryterna hade inget signifikant samband och låg korrelation. KONKLUSION: Resultaten tyder på hög skadeprevalens inom GMU, framförallt hos kvinnliga rekryter. Något samband mellan självskattad nivå av fysisk aktivitetsnivå och skade-/besvärsprevalens i nedre extremitet fanns inte hos rekryterna. Sambandet fanns varken för män eller kvinnor på gruppnivå.

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