Problem Statement: Stepping is a common strategy after a perturbation. Stroke survivors display a predilection for stepping with non-paretic leg. Insight into induced stepping between stroke survivors and age-matched control may guide our understanding for reactive postural control training post stroke. Purpose: To investigate the difference in perturbation-induced stepping between chronic stroke survivors and age-matched controls at three phases of the stepping response: preparation, execution, and landing and association with clinical outcome measures. Procedure: Twenty-one community-dwelling chronic stroke survivors (mean age 59y/o ±13yrs) and 17 age- and gender-matched controls (mean age 54.4y/o ±17yrs) completed this study. Clinical measures of gait, balance, range, sensation, and motor control were assessed. A mechanical weight drop of 10% body weight (BW) was used to create the anterior waist pull perturbation during three stance symmetry positions: equal stance (EQ) and two asymmetrical stance (70% BW on dominant leg and 70% BW on nondominant leg). Ten perturbation trials plus two catch trials at 2% BW were given in a standard randomly order at the three stance positions. Kinematic and kinetic data was collected for perturbation steps. Results: The asymmetrical trials resulted in two types of stepping response, steps with the leg bearing 70% BW (loaded steps – LS) and steps with the leg that had 30% BW (unloaded steps – ULS). All subjects initiated steps more often with their unloaded leg (ULS) in the asymmetrical stance trials. In the stroke group the ULS increased paretic leg stepping compared to EQ (p=0.001) and LS (p=0.001). The stroke group had significantly earlier APA onset with both non-paretic leg (p=0.003) and paretic leg (p=0.028), took significantly more steps with paretic (p=0.01) and non-paretic (p=0.07), shorter step length (paretic, p=0.025 and non-paretic p=0.003), and less change in momentum at landing with paretic leg (p=0.01) compared to controls. Conclusion: Reacting to a perturbation is more challenging for chronic stroke survivors than age- and gender-matched control subjects in the preparation, execution, and landing phase of the stepping response regardless of the leg used. Perturbation training should include stepping with both non-paretic and paretic leg.

Falls are the leading cause of injuries among older adults (>65) and frequently result in reduced mobility, loss of independence, decreased quality of life, injury, and death.  Extensive research has been conducted regarding postural coordination and control, and other mechanisms/processes involved in maintaining postural stability.  However, there is relatively limited knowledge regarding the patterns of joint coordination, the underlying postural controller, and efficient methods to assess passive and active musculoskeletal properties relevant to balance.  In the current work, three new methods were developed to address these limitations and also to better understand the effects of localized ankle muscle fatigue, gender, and aging on postural coordination and control. First, two methods were used to evaluate postural coordination.  A wavelet coherence approach was developed and applied to assess the level and pattern of coordination between pairs of joints (i.e., ankle-knee, ankle-trunk, and ankle-head).  In addition, the uncontrolled manifold method was implemented for evaluation of potential whole-body coordination control goals.  Clear patterns of intermittent wavelet coherence were evident, indicating that joint coordination is intermittently executed.  Both in-phase and anti-phase coherence were detected over frequencies of 2.5 -- 4.0 Hz.  Shoulder and head kinematics appeared more likely than the whole-body center of mass as control goals for whole body coordination.  Both aging and ankle muscle fatigue led to a reduction of joint coordination. Second, an intermittent sliding mode controller was developed to model quiet upright stance.  In contrast to most previous postural controllers, which assume continuous control, an intermittent controller was considered more consistent with recent evidence on muscle activity and the results of the first study on postural coordination.  The sliding mode controller was able to accurately track kinematics and kinetics, and generated passive and active ankle torques comparable with previous results.  Ankle fatigue led to an increase in active ankle torque especially among young adults and males. Third, a new method was developed to estimate passive and active mechanical properties at the ankle (e.g., stiffness and damping).  This method was inspired from intermittent control theory, and the earlier results noted.  As opposed to conventional methods, this new method is computationally efficient and does not require external mechanical or sensory perturbations.  The method yielded a ratio of passive to active ankle torques consistent with earlier evidence, and larger passive and active ankle torques among males and older adults.  A post-fatigue increase of active ankle torque was estimated, especially among males and young adults. In addition to providing new analytical methods, the noted studies suggest that older adults have decreased joint coordination and increased ankle stiffness.  As a practical implication of this, fall prevention training programs may benefit from seeking to develop appropriate joint coordination strategies and ankle stiffness magnitudes.  To expand on the current work, future research should consider measuring muscle contraction characteristics at multiple joints and in different postures or activities. / Ph. D.

Title Energy expenditure of slackline walking Objectives The aim of this study was to investigate the energy expenditure of slacklining in intermediate and advanced slackliners. Methods In this observatory study, 19 slackliners (10 intermediate, of which 7 men and 3 women, 9 advanced, of which 7 men and 2 women) completed experimental energy expenditure measurement of slacklining using indirect colorimetry. The MetaMax 3B metabolic analyzer (Cortex Biophysik, Germany) was used to determine respiratory parameters and the heart rate monitor (Polar Electro OY, Finland) was used to determine the heart rate (HR). Comparative statistical tools were used in the data analysis. Results Relative energy expenditure of 0,471 kJ·min-1 ·kg-1 was found in intermediate slackliners and 0,377 kJ·min-1 ·kg-1 in advanced slackliners in walking on a 10 m long slackline at a constant speed of 15 m·min-1 . In the static standing on slackline, the relative energy expenditure was found to be 0.368 kJ·min-1 ·kg-1 in intermediate slackliners and 0.289 kJ·min-1 ·kg-1 in advanced slackliners. The weighted arithmetic mean for HR in men and women walking on the slackline at 15 m·min-1 was at 67.3% of the predicted HRmax (220 - age for men, 226 - age for women). The MET value in the advanced group (n = 10) was set at 5.15, and in...

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Des évidences suggèrent que l’entraînement golfique améliore l’acuité proprioceptive et la stabilité posturale. Cependant, la proprioception du membre supérieur des golfeurs experts n’a jamais été évaluée. De plus, aucune étude ne s’est intéressée à la demande attentionnelle de la performance motrice des golfeurs élites. Nous avons comparé la performance de golfeurs élites à celle de non-athlètes sédentaires dans deux tâches motrices effectuées sans vision : une tâche d’atteintes manuelles vers des cibles proprioceptives situées dans l’espace tridimensionnel et une tâche de limites de la stabilité posturale dynamique. Ces tâches étaient effectuées isolément (tâche simple) ou simultanément à une tâche cognitive attentionnelle de soustraction mathématique (tâche double). La précision et la variabilité des atteintes manuelles étaient mesurées à l’aide d’un système d’analyse de mouvement. Les limites de la stabilité posturale étaient quantifiées à partir des déplacements des centres de pression obtenus à l’aide d’une plateforme de force. Nos résultats démontrent que les atteintes manuelles des golfeurs élites sont moins variables que ceux des sujets témoins uniquement dans la condition de tâche double. La performance cognitive des golfeurs est également meilleure que celles des sujets témoins en condition de tâche double. Par ailleurs, les limites médio-latérales de la stabilité posturale des golfeurs élites sont plus grandes que les non-athlètes et mobilisent, en moyenne, moins de ressources attentionnelles. Ensemble, ces résultats suggèrent que l’entraînement golfique augmente l’efficacité de contrôle proprioceptif des mouvements de bras et de la stabilité posturale et diminue les exigences attentionnelles de la performance motrice. / Evidence suggests that golf training improves proprioceptive acuity and postural stability. However, proprioceptive sensitivity at the upper limb has never been investigated in expert golfers. Furthermore, no previous study assessed the attentional demand of motor performance in elite golfers. We compared the performance of elite golfers to sedentary non-athletes in two motor tasks performed without vision: a task involving reaching movements to proprioceptive targets located in three-dimensional space and a dynamic postural stability limit task. These tasks were performed alone (single-task) and simultaneously to a cognitive-attentional subtraction task (dual-task). The accuracy and variability of reaching movements were measured using a motion analysis system. The limits of postural stability were quantified from center of pressure displacements recorded with a force platform. Our results demonstrated that reaching movements of elite golfers were less variable than those of control subjects only in the dual task condition. As well, the cognitive performance of elite golfers was better than those of non-athletes in the dual task condition. Moreover, the medio-lateral stability limits of elite golfers were larger than those of non-athletes and, on average, mobilized less attentional resources. Together, these results suggest that golf training increases the efficiency of the proprioceptive control of arm movements and postural stability and decreases the attentional demand of motor performance.

In people with Multiple Sclerosis (MS) balance impairments may lead to increased falls and mobility loss. In quiet stance, people with MS display greater postural sway than healthy controls. Tai Chi is a Chinese martial art that has decreased the risk of falling in frail elderly individuals (Wolf et al., 1996). The purpose of this study was to determine if a three week Tai Chi intervention would improve postural stability in people with MS. Seven participants (6F/1M, age 48.5 ± 10.8 years, height 1.66 ± 0.08m, mass 68.6 ± 19.8kg) attended nine one hour training sessions to practice two types of Tai Chi: standing meditation and slow walking. Postural stability was assessed before and after training using average center of pressure (CoP) velocity, total excursion and time to contact (TtC) for the static trials, and dual and single limb support times for the walking trials. To measure postural stability trials of quiet stance (QS), Tai Chi standing meditation with (SMA) and without arms (SM), tandem stance (TS), preferred speed walking (PW) and slow speed walking (SW) were assessed. Kinematic data recorded by a 12 camera motion capture system (Qualysis AB), and kinetic data collected from a single forceplate (AMTI) were used to compute net CoP. Because functional parameters can influence stability, strength obtained from a chair rise test and neural drive obtained from a foot tapping test were obtained. All results were assessed with paired t-tests (p.05). For SMA, average CoP velocity (p=.006) and excursions (p=.023) increased, and average TtC (p=.020) was reduced. For TS average CoP velocity (p=.06) and excursions (p=.09) trended towards decreased values, and average TtC (p=.045) increased. With the exception of increased left single limb support time (p=.009) PW and SW were not affected by the intervention. In conclusion, the increased neural drive, muscular strength, and postural stability in TS supports the idea that a three week Tai Chi intervention is effective at improving static balance in people with MS.

Virtual reality (VR) is becoming increasingly important in balance training. However, the influence of VR generated visual perturbation, through the novel virtual moving room paradigm, is unknown. Thirty healthy individuals had their static balance assessed on a BTrackS balance plate under eight different conditions: baseline eyes open and eyes closed with and without VR, unexpected toward and away moving VR perturbation, and expected toward and away moving VR perturbation. Multiple statistical analyses were conducted, and the results revealed significantly higher postural sway variables in the unexpected moving toward trials compared to the other moving room conditions; significantly higher postural sway variables in the eyes open no VR compared to VR; and significantly higher postural sway variables in the eyes closed no VR compared to VR. This study provides evidence that VR can be used as a safe and low-cost balance training tool by exposing individuals to fall-prone situations and increasing their balance confidence.

Context: Chronic ankle instability (CAI) individuals experience residual symptoms including pain, swelling, ankle instability, etc. A small majority of CAI individuals report ankle pain during daily or physical activity. Despite the known negative effects of chronic pain on neuromuscular control, there is a paucity of research exploring the specific impact of chronic pain mechanisms on altered neuromuscular control in CAI individuals. Purpose: The purpose of this study was to identify the effects of pain levels on static and dynamic postural control and visual reliance in CAI individuals. Methods: A total of 60 participants were recruited, consisting of 20 CAI individuals with high pain, 20 CAI individuals with low pain, and 20 healthy controls. Participants performed static postural control with eyes open and closed, the star excursion balance test (SEBT), and single-leg hop stabilization. One-way ANOVA assessed differences in Romberg ratios, SEBT, dynamic postural stability index, and self-reported outcomes. Two-way ANOVA (3x2) was used to assess differences in static postural control across the three groups. Results: The high pain group showed decreased mediolateral (ML) direction of static postural stability in eyes closed and a higher Romberg ratio in ML direction compared to the low pain group. The high pain group showed decreased reach distance and increased dynamic postural control in vertical and dynamic postural stability index compared to the healthy control group and low pain group, respectively. Conclusions: The levels of chronic pain can have a significant impact on both static and dynamic postural control and visual reliance in CAI individuals. Therefore, fluctuating chronic pain levels may result in alterations in motor outcomes.

Theoretical part of the thesis summarizes state of art in the field of interaction of sound stimuli with the vestibular system and balance control. Further it summarizes the effect of cochlear implantation on the peripheral vestibular structures and on the stance stability. Cochlear implantation is effective way of hearing rehabilitation. Nevertheless surgery in the region of the inner ear results in reduction of function of the peripheral vestibular structures on the implanted side. The functional deficit of the peripheral vestibular system induced by the surgery is well tolerated by patients and quickly spontaneously subside. Sound available to the patients after implantation is one of the important modalities needed for balance control. In patients with balance deficit was found higher reliance on hearing when maintaining stable stance. Some sounds can reduce postural sway. Namely listening to the broadband noise (such as white and pink) results in reduction of postural sway. The balance control also relies on the ability to localize sound source. Information about position of sound source can be utilized as point of reference for driving balance reactions. Experimental part of the thesis quantifies changes in stance stability in patients with cochlear implants using stabilometry. The...

Context: Knee pain is experienced by many people. Because of this, authors have started researching the effects of pain on lower extremity mechanics and also on static and dynamic postural control. However, the effects of pain are difficult to study due to associated confounding variables. Objective: We asked: (1) Will experimentally-induced anterior knee pain alter perceived pain using the visual analogue scale? ; (2) will perceived pain affect postural control as measured by center-of-pressure during static and dynamic movement? Design: Crossover. Setting: Biomechanics laboratory. Participants: Fifteen healthy subjects. Intervention: Each subject participated in single leg quiet stance, landing, and walking trials under three conditions (pain, sham, control), at three different times for each condition (pre-injection, injection, and post-injection). Main Outcome Measures: The dependent variables were measured at pre-injection, injection, and post-injection. Pain was measured using the visual analogue scale across all three times during each condition. Center-of-pressure sway was measured during single leg quiet stance to calculate the average center-of-pressure velocity in the anterior-posterior and medial-lateral directions. The center-of-pressure time to stabilization was measured in anterior-posterior, medial-lateral, and vertical directions, and center-of-pressure trajectory excursion was measured in the medial-lateral direction during walking. Results: Perceived pain was significant (P < 0.05) but did not affect postural control as measured by center-of-pressure medial-lateral and anterior-posterior sway during single leg quiet stance, in time to stabilization during landing, and in medial-lateral excursion during walking. Conclusions: Injection of hypertonic saline resulted in statistically significant perceived pain but did not affect postural control as measured by center-of-pressure medial-lateral and anterior-posterior sway during single leg quiet stance, in time to stabilization during landing, and medial-lateral excursion during walking.