Background: The most common injuries in new or novice runners include medial tibial stress syndrome and patellofemoral pain syndrome; both overuse injuries. It is known that novice runners use a rearfoot strike pattern 98% of the time while running in traditional running footwear. Furthermore, footwear that is constructed with less cushioning (minimal shoes) and is said to promote forefoot running has increased in popularity. It is still unknown if novice runners convert their strike pattern in minimal shoes or continue to use a rearfoot strike pattern. Consequences of continuing to use a rearfoot strike pattern with less cushioning underfoot include higher vertical loading rates which are directly related to the types of injuries experienced. Aside from the strike pattern in a given shoe, movement stability is an important feature in healthy locomotion. There is a trade-off between being overly stable and being too unstable while running. It is known that the level of experience in running is related to the amount of stride length variability. It is still unknown if altering midsole stiffness has an effect on local dynamic stability while running. Purpose: The primary purpose of this thesis was to compare landing kinematics and kinetics between trained and novice runners in minimal and traditional shoes. The secondary purpose of this thesis was to examine the effect of running experience and midsole construction on local dynamic stability at the ankle, knee and hip. Methods: Twelve trained runners and twelve novice runners were recruited for participation. Four prototypical shoe conditions were tested with midsole geometry and material stiffness being manipulated. This yielded traditional/soft, traditional/hard, minimal/soft and minimal/hard shoe conditions. Participants ran down a 30m indoor runway which was instrumented with force platforms to measure vertical loading rates and motion capture cameras to capture landing kinematics. Participants also ran on a treadmill in each shoe condition to allow for local dynamic stability to be estimated at the ankle, knee and hip in the sagittal plane. Results: Novice runners landed with increased knee extension compared to trained runners. Increasing midsole thickness of the shoes caused an increase in dorsi-flexion of the ankle at heel strike. Manipulating material stiffness did not influence landing kinematics but did influence kinetics. Furthermore, decreasing material stiffness lowered vertical loading rates. Trained runners exhibited increased local dynamic stability (more stable) at the ankle, knee and hip compared to novice runners. Local dynamic stability was not affected by midsole stiffness. Conclusions: Novice runners did not alter their strike pattern in minimally constructed shoes. For this reason, cushioning properties of the shoe dictated vertical loading rates upon the body. Shoe conditions did not alter landing kinematics above the ankle, which is where the between group differences existed as novice runners landed with a more extended knee. Running experience appears to play a role in knee orientation at landing and is unaffected by shoe condition. Local dynamic stability was affected by running experience and does not appear to be related to the shoe condition being worn. Even when kinematics changed across shoe conditions, the stability of the movement did not.

Flow-like mass movement is the most destructive landslide and causes loss of lives and substantial property damage throughout the world every year. This thesis focuses on the spatial and temporal changes of the mass movement in terms of velocity and displacement within the failure mass, and the spatial and temporal distribution of the three dimensional internal deformation of the granular slopes using discrete element method, physical experiments, and natural landslides. We have also studied the effect of weak horizons on the kinematics and internal deformation of granular slopes. Numerical model results show the following features related to a failure mass. The failure mass flows downwards in an undulating pattern with a distinctive velocity heterogeneity. Dilatation within the failure mass is strongly dependent on its mechanical properties. A larger mass moves downslope and the mass moves faster and further in the model with lower internal friction and cohesion. The presence of weak horizons within the granular slope strongly influences displacement, location of the failure surface, and the amount of the failure mass. In addition, results from analogue models and natural landslides are used to outline the mode of granular failure. The collapse of granular slopes results in different-generation extensional faults in the back of the slope, and contractional structures (overturned folds, sheath folds and thrusts) in the toe of the slope. The first-generation normal faults with a steep dip (about 60º) cut across the entire stratigraphy of the slope, whereas the later-generation normal faults with a gentle dip (about 40º) cut across the shallow units. The nature of the runout base has a significant influence on the runout distance, topography and internal deformation of a granular slope. Good agreements are found between models and nature for the collapse of granular slopes in terms of the similar structural distribution in the head and toe of the failure mass and different generations of failure surfaces. The presence of a weak horizon within the granular slope has a significant influence on the granular failure and three dimensional internal deformation of the failure mass.

Actions are goal-directed. It can be the goal of an action to change the environment (i.e. to produce an effect), but also to change one´s own situation in the environment (i.e. to move to a physical target). Previous research has shown that kinematics of actions directed towards physical targets are not only mere reactions to such targets. Instead, targets evoke intentional goals. Representations of such intentional goals influence action execution. However, thus far, most studies in the context of the ideomotor theory of action control have focused on the influence of anticipated action effects on action planning. The role of targets as action goals as well as the role of goal anticipations on overt action execution has mostly been neglected. In this dissertation the role of goal representations in action control was investigated. The ideomotor theory served as a theoretical framework. It was assumed that targets function as action goals similar to action effects and that action goals influence action execution by the anticipation of upcoming events. Action execution towards targets and towards effects was compared. This was done in the temporal and the spatial domain. Furthermore, goal representations were manipulated in order to evaluate their influence on action execution and to disentangle the role of physical target characteristics and the role of goal representations. The findings obtained strengthen the assumption that goal representations play an important role in action control. First, both targets and effects can be viewed as goals of an action in the temporal and spatial domain. Second, movement kinematics are shaped by the way targets are represented as action goals, rather than by physically target properties. In conclusion, as goal representations are formed before the action is actually executed they influence action execution by the anticipation of upcoming events. The ideomotor theory of action control should incorporate action targets as goals similar to action effects.

Postural control incorporates multiple neural and mechanical systems at various levels of the motor control system, yet the question of how all these systems interact remains unanswered. This dissertation describes development of a biologically based, three-dimensional mathematical model of the forelimb of the domestic cat that integrates skeletal anatomy, muscular architecture, and neural control. Previous work has shown that muscle architecture profoundly affects its function. However, even though the forelimbs of quadrupeds contribute to posture and locomotion differently from hindlimbs, most models of quadruped motion are based upon hindlimb mechanics. The proposed work consists of three main steps: (1) architectural and anatomical characterization, which involves acquisition of muscle attachment data, measurement of whole muscle and muscle fiber properties, and estimation of limb kinematic parameters; (2) model development and implementation, wherein the data will be integrated into a mathematical model using special-purpose software; and (3) model validation, including verification of model estimates against experimentally obtained measurements of muscle moment arms, and prediction of limb kinetics, namely end-point forces arising from perturbations to the limb. It was found that the forelimb does indeed possess structure, particularly at the shoulder and antebrachium, that allows for more diverse movements. The neural wiring in these regions is more complex than in the hindlimb, and there exists substantial muscular structure in place for non-sagittal motion and object suppression and retrieval. Other results showed that the kinematics of the limb alone produce a restorative response to postural disturbance but that the magnitude is reduced, indicating that neural input acts as a modulatory influence on top of the intrinsic mechanism of limb architecture. Furthermore the model demonstrated many of the essential features found in the experiments. This study represents the implementation of the first forelimb model of the cat incorporating mechanical properties and serves as a key component of a full quadruped model to explore posture and locomotion.

New surgical approaches for total hip arthroplasty (THA) are being developed to reduce muscle damage sustained during surgery, in the hope to allow better muscle functioning afterwards. The goal of this study was to compare the muscle sparing anterior (ANT) approach to a traditional lateral (LAT) approach with three-dimensional motion analysis. Kinematics and kinetics were obtained with an infrared camera system and force plates. It was hypothesized that (1) the ANT group would have closer to normal range of motion, moments and powers, compared to the LAT group, and that (2) the ANT group would have higher peak hip abduction moment than the LAT group. Forty patients undergoing unilateral THA for osteoarthritis between the ages of 50 and 75 (20 ANT, 20 LAT) were asked to perform three trials of walking, stair ascent and stair descent. Patients were assessed between six to twelve months postoperatively. Twenty age- and weight-matched control participants (CON) provided normative data. Results indicated that both THA groups had gait anomalies compared to the CON group. Both THA groups had reduced hip abduction moment during walking (CON vs. ANT: p<0.001; CON vs. LAT: p=0.011), and the ANT group had a significantly lower hip abduction moment compared to the LAT group (p=0.008). Similar results were observed during stair descent, where the ANT group had reduced peak hip abduction moment compared to the CON group (p<0.001) and the LAT group (p=0.014). This indicates that the anterior approach did not allow better gait and stair climbing ability after THA. It is therefore thought that other variables, such as preoperative gait adaptations, trauma from the surgery, or postoperative protection mechanisms to avoid loading the prosthetic hip, are factors that might be more important than surgical approach in determining the mechanics of THA patients after surgery.

Tai Chi Chuan is a safe alternative for those who wish to improve balance and physical wellbeing. It is a popular form of exercise that is supported by a growing body of research aimed towards improving the health of a sedentary elderly population. The purpose of this study was to examine the biomechanical features of the lower extremity during performance of two Tai Chi movements, the “Repulse Monkey (RM)” and “Wave-hands in clouds (WHIC).” The study’s parameters included quantitative measures of the temporospatial, kinematic, and kinetic characteristics of the lower extremities. A group of experienced male Tai Chi practitioners (n = 15) between the ages of 65 to 75, performed “Repulse Monkey (RM)”, “Wave-hand in Cloud (WHIC)”, and forward walking. Three-dimensional (3-D) kinematic and kinetic data was collected using VICON motion analysis system with 10 infrared cameras and 4 force plates. The following variables were examined: stride width, step length, step width, single- and double-support times, centre of mass (COM) displacement, peak joint angles, range of motion, peak joint moments, time to peak moment, and ground reaction force (GRF). The differences in the measurements of the two Tai Chi movements were compared with walking using two-way ANOVA. The study’s results showed that the two Tai Chi movements elicit gentle and fluid changes to position of the upper body mass and the joints in the lower extremity. In terms of joint kinematics, the knee remained flexed throughout RM and WHIC. Unlike walking, RM had larger abduction and adduction angles at the knee joints and large plantar- and dorsiflexion ROM at the ankle. Reduced posterior, mediolateral, and vertical GRF were seen; the loading joints at the ankle and hip were gentle and smaller than walking. Varus/valgus moments were notably larger at the knee joint during RM and eversion moment was larger at the ankle joint during WHIC movement. A large, but slow loading rate at the knee joint has implication towards the viscoelastic properties of the knee. A better understanding of RM and WHIC would facilitate the improvement of balance, physical capacity, and joint flexibility for the elders.

Patellofemoral pain (PFP) is believed to be associated with deficits in coordination between the different heads of the quadriceps muscle; however, considerable debate exists in the literature regarding the presence of such a deficit. Discrepancies between studies may be explained by differences in experimental tasks, such as whether the task is performed with open (OKC) or closed kinetic chain (CKC), or whether the activity is voluntary or triggered. Particular interest has been directed toward the function of the vastus medialis obliquus (VMO), which is a short muscle with limited ability to exert torque across the knee joint, but probably has a particular role in controlling patellofemoral joint position. Another short muscle that may influence knee joint position control is popliteus (POP), which is located in the back of the knee. This thesis investigates task specific activity of quadriceps in CKC versus OKC and studies the relative activity between the four heads of the quadriceps in PFP subjects compared to controls without knee pain in voluntary activity (CKC and OKC) and postural responses to balance perturbations. In addition, this thesis investigates the presumed function of POP for control of joint position in postural tasks in healthy individuals. All subjects were of normal weight and height and between 18 and 40 years. Quadriceps activity was tested for isometric with identical joint configuration in CKC and OKC, and it was performed as a reaction time task. Balance perturbations were elicited by unpredictable anterior and posterior translations of the support surface. Function of POP was investigated in unpredictable support surface translations and in self induced provocations to balance by moving the arms. Muscle activity was recorded with electromyography (EMG). Optic kinematic analysis was used to obtain specific movement responses to perturbations of balance. The quadriceps muscles were activated differently in CKC and OKC. VMO was activated earlier and to a greater degree in CKC. Rectus femoris was activated earlier and to a greater degree in OKC. PFP subjects reacted slower in both CKC and OKC, but there was no difference between groups in the relative activity between the different heads of the quadriceps. In the unpredictable support surface translation in the anterior direction, PFP subjects responded with earlier onset of VMO and with greater trunk and hip flexion in the anterior translation. POP activation in response to support surface translations in both directions occurred before all other muscles measured. In the self-initiated provocations of balance, POP was activated after the initiation of the balance provocation. This thesis concludes that quadriceps activity was task specific. The lack of difference between groups in OKC and CKC, and the difference between groups in postural responses suggest that variations in motor behaviour may occur only in tasks habitually performed. Differences in muscle activation patterns may be related to compensatory strategies to unload the quadriceps muscles and the patellofemoral joint. Furthermore, this thesis suggests that POP muscle may have a particular role in active control of the knee joint.

Knee function after more than 20 years post injury is rarely described and none of the few follow-up studies have evaluated functional performance tasks. This thesis investigated self-reported knee function, physical activity level, physical capacity and movement pattern in the long-term perspective (on average 23 years) in persons who had suffered a unilateral ACL injury, treated either with physiotherapy in combination with surgery (ACLR, n=33) or physiotherapy alone (ACLPT, n=37) and compared to age-and-gender matched controls (n=33).  This thesis shows that regardless of treatment, there are significant negative long-term consequences on self-reported knee function and physical activity more than 20 years after injury. In comparison to the controls, the ACL-groups (ACLR and ACLPT) had lower knee function as measured by the Lysholm score and the Knee injury and Osteoarthritis Outcome Score (KOOS). The persons with an ACL injury also had a lower knee-specific physical activity level (Tegner activity scale), while no differences were seen in general physical activity level (International Physical Activity Questionnaire, IPAQ) compared to healthy controls. Regarding physical capacity, both ACL groups showed inferior jump capacity in the injured leg compared to the non-injured leg. However, compared to controls the ACL-injured had a relatively good jump performance. Knee extension peak torque, concentric and eccentric, was also lower for the injured leg compared to the non-injured leg for both ACLR and ACLPT. In addition, the ACLPT group showed reduced eccentric knee flexion torque of the injured leg. The non-injured leg, on the other hand, showed almost equal jump capacity and strength as controls. Balance in single-limb stance (30s) was inferior in persons who had an ACL injury. This was true for both the injured and non-injured leg and regardless of treatment. Movement pattern during the one-leg hop was analysed by a set of kinematic variables consisting of knee angles (flexion, abduction, rotation) and Centre of Mass (CoM) placement in relation to the knee and ankle joints. Both ACLR and ACLPT displayed movement pattern asymmetries between injured and non-injured legs. In comparison to controls, the ACLR group had a similar movement pattern with the exception of larger external knee rotation at Initial contact and less maximum internal rotation during the Landing. ACLPT showed several differences compared to controls both regarding knee angles and CoM placement. The ACL-injured persons with no-or-low knee osteoarthritis (OA) had better knee function as reflected by higher scores on Lysholm and KOOS subscale ‘symptom’ compared to those with moderate-to-high OA. The degree of OA had no influence on reported physical activity level, jump capacity, peak torque or the kinematic variables.  In conclusion, this thesis indicates that persons with a unilateral ACL injury, regardless of treatment, have some negative long-term consequences e.g. self-reported knee function, knee-specific activity level, strength and balance deficits, when compared to age-and-gender matched controls. The results, however, also indicate that the ACL-injured can manage reasonably well in some jumps and general activity level but have an inferior performance in more knee-demanding tasks. The ACLR group had similar movement pattern with the exception of knee rotation, indicating that a reconstruction may restore the knee biomechanics to some extent. The ACLPT group on the other hand, seem to use compensatory movement strategies showing several differences compared to controls.

This thesis evaluated energy levels, muscle activity, and upper limb kinematics during AVG play in children with cerebral palsy (CP). For context, a systematic review was conducted, which found that AVGs elicited light to moderate physical activity in typically developing children. In children with CP, moderate levels of physical activity were achieved for Dance Dance Revolution and Wii Boxing, while light levels of physical activity were achieved for Wii Bowling and Wii Tennis. Muscle activity was highest during Wii Boxing, but remained below the maximum voluntary effort for all games and muscles. Angular velocities and accelerations were significantly larger in the dominant limb compared to the hemiplegic limb. When children played against a real opponent, dominant arm activity increased, while hemiplegic arm activity decreased. The results of this thesis indicate that AVGs may be an enjoyable and relatively safe option for children with CP to attain moderate physical activity.

This thesis evaluated energy levels, muscle activity, and upper limb kinematics during AVG play in children with cerebral palsy (CP). For context, a systematic review was conducted, which found that AVGs elicited light to moderate physical activity in typically developing children. In children with CP, moderate levels of physical activity were achieved for Dance Dance Revolution and Wii Boxing, while light levels of physical activity were achieved for Wii Bowling and Wii Tennis. Muscle activity was highest during Wii Boxing, but remained below the maximum voluntary effort for all games and muscles. Angular velocities and accelerations were significantly larger in the dominant limb compared to the hemiplegic limb. When children played against a real opponent, dominant arm activity increased, while hemiplegic arm activity decreased. The results of this thesis indicate that AVGs may be an enjoyable and relatively safe option for children with CP to attain moderate physical activity.