Predictors of weight loss in Parkinson's disease: is weight loss the chicken or the egg?
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Disease Progression↗
Biomedical subjects
Martin Simoneau
Publications and source records attributed to Martin Simoneau.
Plasma concentration of organochlorine compounds is associated with age and not obesity.
It has been suggested that obese individuals, because of an increased dilution space (body fat) for lipophilic organochlorines compounds, may have greater levels of toxic pollutants than lean sedentary individuals. It is important to further examine this possibility because of the potential contribution of organochlorine pesticides in the development of Parkinson's disease and other neurological diseases. The aim of this study was to further investigate the relationship between the magnitude of obesity and the plasma concentration of organochlorines for a wide range of BMI (with participants at steady state body weight). Fifty-three individuals were selected on the basis of their body mass index (BMI): lean controls (n=16; mean BMI 22.8+/-2.2 kg/m(2); mean age 38.8+/-9.4 years), obese individuals (n=19; mean BMI 33.4+/-3.0 kg/m(2); mean age 38.6+/-7.6 years) and morbidly obese individuals (n=18; mean BMI 49.3+/-6.5 kg/m(2); mean age 44.3+/-9.2 years). Blood samples were analyzed for organochlorine compounds. The relationship between the total plasma organochlorine concentration and BMI was tested using a multiple regression analysis. Age was included in the model. There was no relationship between the total plasma organochlorine concentration and BMI. Organochlorine concentrations, however, were correlated with age (BMI-adjusted R(2)=0.46; p<0.001). At steady state body weight, toxic pollutant concentrations are not associated to obesity but strongly correlate with age.
Adult↗
Altered sensory-weighting mechanisms is observed in adolescents with idiopathic scoliosis.
BACKGROUND: Scoliosis is the most common type of spinal deformity. In North American children, adolescent idiopathic scoliosis (AIS) makes up about 90% of all cases of scoliosis. While its prevalence is about 2% to 3% in children aged between 10 to 16 years, girls are more at risk than boys for severe progression with a ratio of 3.6 to 1. The aim of the present study was to test the hypothesis that idiopathic scoliosis interferes with the mechanisms responsible for sensory-reweighting during balance control. METHODS: Eight scoliosis patients (seven female and one male; mean age: 16.4 years) and nine healthy adolescents (average age 16.5 years) participated in the experiment. Visual and ankle proprioceptive information was perturbed (eyes closed and/or tendon vibration) suddenly and then returned to normal (eyes open and/or no tendon vibration). An AMTI force platform was used to compute centre of pressure root mean squared velocity and sway density curve. RESULTS: For the control condition (eyes open and no tendon vibration), adolescent idiopathic scoliosis patients had a greater centre of pressure root mean squared velocity (variability) than control participants. Reintegration of ankle proprioception, when vision was either available or removed, led to an increased centre of pressure velocity variability for the adolescent idiopathic scoliosis patients whereas the control participants reduced their centre of pressure velocity variability. Moreover, in the absence of vision, adolescent idiopathic scoliosis exhibited an increased centre of pressure velocity variability when ankle proprioception was returned to normal (i.e. tendon vibration stopped). The analysis of the sway density plot suggests that adolescent idiopathic scoliosis patients, during sensory reintegration, do not scale appropriately their balance control commands. CONCLUSION: Altogether, the present results demonstrate that idiopathic scoliosis adolescents have difficulty in reweighting sensory inputs following a brief period of sensory deprivation.
Adolescent↗
The effects of moderate fatigue on dynamic balance control and attentional demands.
BACKGROUND: During daily activities, the active control of balance often is a task per se (for example, when standing in a moving bus). Other constraints like fatigue can add to the complexity of this balance task. In the present experiment, we examined how moderate fatigue induced by fast walking on a treadmill challenged dynamic balance control. We also examined if the attentional demands for performing the balance task varied with fatigue. METHODS: Subjects (n = 10) performed simultaneously a dynamic balance control task and a probe reaction time task (RT) (serving as an indicator of attentional demands) before and after three periods of moderate fatigue (fast walking on a treadmill). For the balance control task, the real-time displacement of the centre of pressure (CP) was provided on a monitor placed in front of the subject, at eye level. Subjects were asked to keep their CP within a target (moving box) moving upward and downward on the monitor. The tracking performance was measured (time spent outside the moving box) and the CP behavior analyzed (mean CP speed and mean frequency of the CP velocity). RESULTS: Moderate fatigue led to an immediate decrement of the performance on the balance control task; increase of the percentage of time spent outside the box and increase of the mean CP speed. Across the three fatigue periods, subjects improved their tracking performance and reduced their mean CP speed. This was achieved by increasing their frequency of actions; mean frequency of the CP velocity were higher for the fatigue periods than for the no fatigue periods. Fatigue also induced an increase in the attentional demands suggesting that more cognitive resources had to be allocated to the balance task with than without fatigue. CONCLUSION: Fatigue induced by fast walking had an initial negative impact on the control of balance. Nonetheless, subjects were able to compensate the effect of the moderate fatigue by increasing the frequency of actions. This adaptation, however, required that a greater proportion of the cognitive resources be allocated to the active control of the balance task.
Journal Article↗
Body weight is a strong predictor of postural stability.
Proper balance control is a key aspect of acitivities of daily living. The aim of this study was to determine the contribution of body weight to predict balance stability. The balance stability of 59 male subjects with BMI ranging from 17.4 to 63.8kg/m(2) was assessed using a force platform. The subjects were tested with and without vision. A stepwise multiple regression analysis was used to determine the independent effect of body weight, age, body height and foot length on balance stability (i.e., mean speed of the center of foot pressure). With vision, the stepwise multiple regression revealed that body weight accounted for 52% of the variance of balance stability. The addition of age contributed a further 3% to explain balance control. Without vision, body weight accounted for 54% of the variance and the addition of age and body height added a further 8% and 1% to explain the total variance, respectively. The final model explained 63% of the variance. A decrease in balance stability is strongly correlated to an increase in body weight. This suggests that body weight may be an important risk factor for falling. Future studies should examine more closely the combined effect of aging and obesity on falling and injuries and the impact of obesity on the diverse range of activities of daily living.
Adult↗
Increased plasma levels of toxic pollutants accompanying weight loss induced by hypocaloric diet or by bariatric surgery.
BACKGROUND: Weight loss reduces the risk of several diseases. Increases of plasma organochlorine and pesticide compounds, however, have been observed with weight loss induced by a dietary intervention and by a gastroplasty. This increased concentration of toxic pollutants could be a side-effect of weight loss and a risk for health problems. The aim of this study was: 1) to observe if there is a relationship between the plasma concentration of organochlorines and BMI at steady state weight, and 2) to determine, after a bariatric surgical intervention, if the magnitude of the weight loss has a direct effect on this concentration. METHODS: Weight loss was obtained in obese individuals by a hypocaloric diet program until resistance and in morbidly obese individuals by a bariatric operation (biliopancreatic diversion - duodenal switch [BPD-DS]). Normal-weight individuals were tested to serve as controls. Blood samples were analyzed for organochlorine and pesticide compounds at baseline in all groups, after resistance to weight loss in obese individuals, and at 3 months and 1 year after surgery in morbidly obese individuals. RESULTS: At steady state weight, organochlorine and pesticide compounds were found in all groups, and the sum of all organochlorine compounds correlated with age and not BMI. Weight loss averaged 12.1% of the initial body weight after dieting and 20.9% at 3 months after surgery, respectively. This weight loss yielded significant increases in total plasma organochlorine concentration (increase of 23.8% for obese and 51.8% for morbidly obese individuals). For morbidly obese individuals, the weight loss at 1 year after surgery (46.3%) yielded a 388.2% increase in total plasma organochlorine concentration. CONCLUSION: Plasma organochlorine concentration increases with weight loss and is related to the magnitude. Future research will have to determine if: 1) this pollutant concentration remains elevated over time and 2) there are long-term effects of this high concentration on health.
Adult↗
Sensory deprivation and balance control in idiopathic scoliosis adolescent.
Balance control is influenced by the availability and integrity of sensory inputs as well as the ability of the balance control mechanisms to tailor the corrective action to the gravitational torque. In this study, to challenge balance control, visual and ankle proprioceptive information were perturbed (eyes closed and/or tendon vibration). We masked sensory inputs in order: (1) to test the hypothesis that adolescent idiopathic scoliosis (AIS), compared to healthy adolescent, relies more on ankle proprioception and/or visual inputs to regulate balance and (2) to determine whether it is the variation or the amplitude of the balance control commands of AIS that leads to greater body sway oscillations during sensory deprivation. By manipulating the availability of the sensory inputs and measuring the outcomes, center of pressure (CP) range and velocity variability, we could objectively determine the cost of visual and/or ankle proprioception deprivation on balance control. The CP range was larger and the root mean square (RMS) of the CP velocity was more variable for AIS than for control participants when ankle proprioception was perturbed. This was observed regardless of whether vision was available or not. The analysis of the sway density curves revealed that the amplitude rather than the variation of the balance control commands was related to a larger CP range and greater RMS CP velocity for AIS. The present results suggest that AIS, compared to control participants, relies much more on ankle proprioception to control the amplitude of the balance control commands.
Adolescent↗
Coordination between posture and movement: interaction between postural and accuracy constraints.
We examined the interaction between the control of posture and an aiming movement. Balance control was varied by having subjects aim at a target from a seated or a standing position. The aiming difficulty was varied using a Fitts'-like paradigm (movement amplitude=30 cm; target widths=0.5, 1.0, 2.5 and 5 cm). For both postural conditions, all targets were within the reaching space in front of the subjects and kept at a fixed relative position with respect to the subjects' body. Hence, for a given target size, the aiming was differentiated only by the postural context (seated vs. upright standing). For both postural conditions, movement time (MT) followed the well-known Fitts' law, that is, it increased with a decreasing target size. For the smallest target width, however, the increased MT was greater when subjects were standing than when they were seated suggesting that the difficulty of the aiming task could not be determined solely by the target size. When standing, a coordination between the trunk and the arm was observed. Also, as the target size decreased, the center of pressure (CP) displacement increased without any increase in CP speed suggesting that the subjects were regulating their CP to provide a controlled referential to assist the hand movement. When seated, the CP kinematics was scaled with the hand movement kinematics. Increasing the index of difficulty led to a strong correlation between the hand speed and CP displacement and speed. The complex organization between posture and movement was revealed only by examining the specific interactions between speed-accuracy and postural constraints.
Adaptation, Physiological↗
The effect of time to peak ankle torque on balance stability boundary: experimental validation of a biomechanical model.
Pai and Patton (1997), using a biomechanical model, determined a set of feasible center of mass (CM) velocity-position combinations (balance stability boundary) that guarantee upright stability. In their study, the magnitude of the restoring ankle torque was used to study the subject's ability to recover balance. Recent studies have suggested that the ability to maintain a stable posture depends not only on the magnitude of the restoring torque but also on the time to generate this torque. The objectives of the present study were: (1) to build a biomechanical model that predicts the balance stability boundary which includes time to peak ankle torque, (2) to determine the capability of the model to predict successful and failed experimental balance recovery trials, and (3) to compare the predictive capability of the biomechanical model with that of a statistical model (logistic regression). A single-link-plus-foot biomechanical model was used to determine a set of balance stability boundaries, computed from the combination of maximum CM velocity and related CM position, for various times to peak ankle torque. An experiment was conducted to validate the biomechanical model. The participants self-initiated a forward destabilization and were asked to regain balance using an ankle feet-in-place strategy. Also, a forward stepwise logistic regression (predictors: CM position and velocity and time to peak ankle torque) was used to discriminate between successful and failed experimental trials. (1) The outcomes of the biomechanical model confirmed that the time to peak ankle torque drastically constrained the stability boundaries. (2) The biomechanical model predicted 79.9% of the failed experimental trials and 74.5% of the successful experimental trials. (3) The stepwise logistic regression included all independent variables and predicted 57.2% of the failed and 93.7% of the successful experimental trials. Hence, the biomechanical model showed better predictive capability than the statistical model for identifying unsuccessful balance recovery. It is noteworthy that the balance stability boundaries constrained by the speed of ankle torque development predicted the outcome of the experimental trial earlier in the time series than balance stability boundary constrained by constant ankle torque. Overall, the present biomechanical model may serve as an assessment tool to develop specific interventions towards improving a patient's speed of ankle torque development and to possibly reduce falling frequency.
Accidental Falls↗
Self-initiating a seated perturbation modifies the neck postural responses in humans.
When seated subjects are submitted to a linear acceleration, reports indicate that the kinematic and electromyographic (EMG) responses of the head-neck system can be modulated with the magnitude of the linear acceleration. There is no evidence, however, that head kinematics or neck EMG activity can be modulated when specific knowledge and active control about the onset of platform acceleration are available. Sixteen seated subjects were given forward linear accelerations in two different conditions nested within subjects: reactive and predictive. In the reactive condition, the acceleration was initiated following a variable delay unknown to the subjects whereas in the predictive condition, subjects manually self-initiated the perturbation. All neck muscle activities were decreased 50-100 ms after platform movement onset in the predictive condition relative to the reactive condition, whereas head and neck peak angular positions and velocities were not different between the two conditions. These results suggest that feedforward control could use the self-generated timing information of platform movement onset to scale the appropriate neck motor output.
Acceleration↗
Attenuation of human neck muscle activity following repeated imposed trunk-forward linear acceleration.
It has been suggested that, after a passive linear acceleration of a seated subject which resembles a small, rear-end car impact, sensory information from proprioceptive, vestibular, and visual systems elicit stabilizing neck muscular responses. These neck muscular responses are presumably reflex based and are modified with the magnitude of the perturbation. A key issue that remains is to determine whether the neck and head postural responses can be modulated by a previous experience of the acceleration and not only by the magnitude of the acceleration. This question is of interest because, contrary to cadaver studies, one could expect that humans apprehending a rapid trunk acceleration would adopt a bracing behavior to minimize head movements. The aim of the present experiment was to verify whether neck-muscle activities can be modulated when prior knowledge about whole-body acceleration onset, direction, and magnitude are unknown compared with when only acceleration onset is unknown. Nine seated subjects were submitted to 11 imposed, forward linear accelerations (1.1 g). For the first trial, subjects were completely unaware of the platform acceleration characteristics (onset, direction, amplitude, and acceleration magnitude). For the subsequent ten trials, subjects knew they would be submitted to a forward linear acceleration, but the onset of the acceleration was unknown. Head kinematics and EMG responses of the neck muscles to the first perturbation were similar for all subjects (6.2 degrees head extension, EMG activity starting from 55 to 72 ms after platform onset). Following the first trial, however, all subjects showed a decreased neck EMG activity. Moreover, subjects responded in one of two ways across trials: one group of subjects ( n=5) maintained a constant head angular position and velocity, whereas the other group ( n=4) showed an increased head angular position (up to 12.6 degrees ) and velocity. This suggests that the first perturbation trial revealed a completely reactive response. After this initial trial, the responses observed may present a mixture of feedforward and feedback control. It is likely that whiplash injuries occur under conditions resembling those observed for the first trial only. If this is the case, the behavior for the following trials cannot be representative of injury mechanisms occurring in whiplash-like motion. Altogether, our results strongly suggest that, following repeated trunk linear accelerations of a constant magnitude, the nervous system prefers to minimize muscle stress instead of adopting a bracing strategy.
Acceleration↗