Félix Berrigan

Reducing weight increases postural stability in obese and morbid obese men

Objective:To investigate the effect of weight loss on balance control in obese and morbid obese men.Methods:In a longitudinal and clinical intervention study, postural stability was measured with a force platform before and after weight loss in men. Weight loss was obtained in obese men (mean body mass index (BMI)=33.0 kg/m2) by hypocaloric diet until resistance and in morbid obese men (mean BMI=50.5 kg/m2) by bariatric surgery. Morbid obese men were tested before surgery, and 3 and 12 months after surgery when they had lost 20 and nearly 50% of initial body weight, respectively. Normal weight individuals (mean BMI=22.7 kg/m2) were tested twice within a 6- to 12-month period to serve as control. Body fatness and fat distribution measures, and posturographic parameters of the center of foot pressure (CP) along the antero-posterior and medio-lateral axes for conditions with and without vision were performed in all subjects.Results:Weight loss averaged 12.3 kg after dieting and 71.3 kg after surgery. Body weight remained unchanged in the control group. After weight loss, nearly all measures of postural stability were improved with and without vision (i.e., CP speed and range in antero-posterior and medio-lateral axes). A strong linear relationship was observed between weight loss and improvement in balance control measured from CP speed (adjusted R 2=0.65, P<0.001).Conclusion:Weight loss improves balance control in obese men and the extent of the improvement is directly related to the amount of weight loss. This should decrease the habitual greater risk of falling observed in obese individuals.

Influence of obesity on accurate and rapid arm movement performed from a standing posture.

Introduction:Obesity yields a decreased postural stability. The potentially negative impact of obesity on the control of upper limb movements, however, has not been documented. This study sought to examine if obesity imposes an additional balance control constraint limiting the speed and accuracy with which an upper limb goal-directed movement performed from an upright standing position can be executed.Method:Eight healthy lean subjects (body mass index (BMI) between 20.9 and 25.0 kg/m2) and nine healthy obese subjects (BMI between 30.5 and 48.6 kg/m2) pointed to a target located in front of them from an upright standing posture. The task was to aim at the target as fast and as precisely as possible after an auditory signal. The difficulty of the task was varied by using different target sizes (0.5, 1.0, 2.5 and 5.0 cm width). Hand movement time (MT) and velocity profiles were measured to quantify the aiming. Centre of pressure and segmental kinematics were analysed to document postural stability.Results:When aiming, the forward centre of pressure (CP) displacement was greater for the obese group than for the normal BMI group (4.6 and 1.9 cm, respectively). For the obese group, a decrease in the target size was associated with an increase in backward CP displacement and CP peak speed whereas for the normal BMI group backward CP displacements and CP peak speed were about the same across all target sizes. Obese participants aimed at the target moving their whole body forward whereas the normal BMI subjects predominantly made an elbow extension and shoulder flexion. For both groups, MT increased with a decreasing target size. Compare to the normal BMI group, this effect was exacerbated for the obese group. For the two smallest targets, movements were on average 115 and 145 ms slower for the obese than for the normal BMI group suggesting that obesity added a balance constraint and limited the speed with which an accurate movement could be done.Summary:Obesity, because of its effects on the control of balance, also imposes constraints on goal-directed movements. From a clinical perspective, obese individuals might be less efficient and more at risk of injuries than normal weight individuals in a large number of work tasks and daily activities requiring upper limb movements performed from an upright standing position.

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.

The effects of muscle strength on center of pressure-based measures of postural sway in obese and heavy athletic individuals.

INTRODUCTION Obesity affects postural sway during normal quiet standing; however, the reasons for the increased postural sway are unknown. Improving muscular strength is regarded as a potential way to improve postural control, particularly for obese and overweight subjects. The purpose of this investigation is to evaluate the role of muscular strength on postural sway in obese and overweight individuals. METHODS Fifteen healthy weight (control group), seventeen obese (obese group) subjects and nine football players (heavy athletic group) participated in this investigation. Isometric knee extension force and postural sway were measured. Muscular strength was calculated in absolute measures as well as relative to body mass (muscular strength to body mass). RESULTS The heavy athletic group demonstrated significantly stronger (absolute) lower limb strength (1593.9 N (95% CI 1425.5, 1762.3)) than both the obese (796.2N (95% CI 673.8, 824.5)) and control (694.1N (95% CI 563.7, 824.5)) groups. As well, when muscular strength was expressed as a ratio to body mass the heavy athletic group had significantly higher values (1.27 (95% CI 1.11, 1.43)) than obese (0.78 (95% CI 0.66, 0.89) and control (1.00 (95% CI (0.88, 1.12)) individuals. Despite this, they swayed similarly to the obese (mean center of pressure speed of 0.83 cms(-1) (95% CI 0.72, 0.93) vs. 0.87 cms(-1) (95% CI 0.80, 0.95)), that is, significantly more than the controls (0.60 cms(-1) (95% CI 0.52, 0.68)). CONCLUSION Isometric knee extensor strength has a minimal effect on postural sway in heavier athletic individuals during normal quiet stance.

Effect of terminal accuracy requirements on temporal gaze-hand coordination during fast discrete and reciprocal pointings.

BackgroundRapid discrete goal-directed movements are characterized by a well known coordination pattern between the gaze and the hand displacements. The gaze always starts prior to the hand movement and reaches the target before hand velocity peak. Surprisingly, the effect of the target size on the temporal gaze-hand coordination has not been directly investigated. Moreover, goal-directed movements are often produced in a reciprocal rather than in a discrete manner. The objectives of this work were to assess the effect of the target size on temporal gaze-hand coordination during fast 1) discrete and 2) reciprocal pointings.MethodsSubjects performed fast discrete (experiment 1) and reciprocal (experiment 2) pointings with an amplitude of 50 cm and four target diameters (7.6, 3.8, 1.9 and 0.95 cm) leading to indexes of difficulty (ID = log2[2A/D]) of 3.7, 4.7, 5.7 and 6.7 bits. Gaze and hand displacements were synchronously recorded. Temporal gaze-hand coordination parameters were compared between experiments (discrete and reciprocal pointings) and IDs using analyses of variance (ANOVAs).ResultsData showed that the magnitude of the gaze-hand lead pattern was much higher for discrete than for reciprocal pointings. Moreover, while it was constant for discrete pointings, it decreased systematically with an increasing ID for reciprocal pointings because of the longer duration of gaze anchoring on target.ConclusionOverall, the temporal gaze-hand coordination analysis revealed that even for high IDs, fast reciprocal pointings could not be considered as a concatenation of discrete units. Moreover, our data clearly illustrate the smooth adaptation of temporal gaze-hand coordination to terminal accuracy requirements during fast reciprocal pointings. It will be interesting for further researches to investigate if the methodology used in the experiment 2 allows assessing the effect of sensori-motor deficits on gaze-hand coordination.

Pre-exercise hyperhydration-induced bodyweight gain does not alter prolonged treadmill running time-trial performance in warm ambient conditions.

This study compared the effect of pre-exercise hyperhydration (PEH) and pre-exercise euhydration (PEE) upon treadmill running time-trial (TT) performance in the heat. Six highly trained runners or triathletes underwent two 18 km TT runs (~28 °C, 25%–30% RH) on a motorized treadmill, in a randomized, crossover fashion, while being euhydrated or after hyperhydration with 26 mL/kg bodyweight (BW) of a 130 mmol/L sodium solution. Subjects then ran four successive 4.5 km blocks alternating between 2.5 km at 1% and 2 km at 6% gradient, while drinking a total of 7 mL/kg BW of a 6% sports drink solution (Gatorade, USA). PEH increased BW by 1.00 ± 0.34 kg (P < 0.01) and, compared with PEE, reduced BW loss from 3.1% ± 0.3% (EUH) to 1.4% ± 0.4% (HYP) (P < 0.01) during exercise. Running TT time did not differ between groups (PEH: 85.6 ± 11.6 min; PEE: 85.3 ± 9.6 min, P = 0.82). Heart rate (5 ± 1 beats/min) and rectal (0.3 ± 0.1 °C) and body (0.2 ± 0.1 °C) temperatures of PEE were higher than those of PEH (P < 0.05). There was no significant difference in abdominal discomfort and perceived exertion or heat stress between groups. Our results suggest that pre-exercise sodium-induced hyperhydration of a magnitude of 1 L does not alter 80–90 min running TT performance under warm conditions in highly-trained runners drinking ~500 mL sports drink during exercise.

Obesity Adds Constraint on Balance Control and Movement Performance

We examined if a weight loss program improves the speed-accuracy tradeoff of goal-directed aiming movements of obese individuals. Ten obese subjects aimed at targets of different sizes from a seated and a standing posture. The kinematics of the aiming was recorded. All participants were evaluated before and after a weight loss program when weight reduction had stabilized. Before weight loss, movement times and duration of deceleration phases were longer when subjects were standing than when they were seated. These effects vanished after weight loss. Weight loss yielded an increased aiming speed when subjects aimed at targets from an upright posture and this effect was greater for the smaller target. This difference was not observed when seated. The results suggest that a more stable postural platform resulting from weight loss allows a better control of the upper-limb movement.

Intestinal temperature does not reflect rectal temperature during prolonged, intense running with cold fluid ingestion.

It is generally assumed that intestinal temperature (Tint), as measured with a telemetric pill, agrees relatively well with rectal temperature (Trec) during exercise. However, whether Tint reflects Trec during prolonged, intense and continuous exercise when cold fluids are consumed is unknown. Therefore, we compared Trec and Tint during a half-marathon during which cold water was ingested to prevent bodyweight (BW) losses >2%. Nine endurance athletes (age 30  ±  5 years) underwent a 21.1 km running time-trial (TT) in the heat (~30 °C and 44% RH) while BW losses were maintained to ~1% with continuous cold (4 °C) water provision. Tint and Trec were monitored throughout the TT. Hypohydration level, TT time and fluid intake were 1.2  ±  0.4% BW, 93.2  ±  9.9 min and 2143  ±  264 ml, respectively. Trec was systematically higher than Tint by 0.25 °C (95% CI: 0.14-0.37 °C). Tint and Trec showed an excellent relative (r = 0.90, p < 0.01), but poor absolute agreement as reflected by a 95% limit of agreement of ±1.07 °C and a standard error of measurement of ±0.39 °C. In conclusion, Tint does not mirror Trec during prolonged, intense running with cold fluid ingestion and, therefore, these measures should not be used interchangeably under this scenario.

Variance in exposed perturbations impairs retention of visuomotor adaptation

Sensorimotor control requires an accurate estimate of the state of the body. The brain optimizes state estimation by combining sensory signals with predictions of the sensory consequences of motor commands using a forward model. Given that both sensory signals and predictions are uncertain (i.e., noisy), the brain optimally weights the relative reliance on each source of information during adaptation. In support, it is known that uncertainty in the sensory predictions influences the rate and generalization of visuomotor adaptation. We investigated whether uncertainty in the sensory predictions affects the retention of a new visuomotor relationship. This was done by exposing three separate groups to a visuomotor rotation whose mean was common at 15° counterclockwise but whose variance around the mean differed (i.e., SD of 0°, 3.2°, or 4.5°). Retention was assessed by measuring the persistence of the adapted behavior in a no-vision phase. Results revealed that mean reach direction late in adaptation was similar across groups, suggesting it depended mainly on the mean of exposed rotations and was robust to differences in variance. However, retention differed across groups, with higher levels of variance being associated with a more rapid reversion toward nonadapted behavior. A control experiment ruled out the possibility that differences in retention were accounted for by differences in success rates. Exposure to variable rotations may have increased the uncertainty in sensory predictions, making the adapted forward model more labile and susceptible to change or decay.NEW & NOTEWORTHY The brain predicts the sensory consequences of motor commands through a forward model. These predictions are subject to uncertainty. We use visuomotor adaptation and modulate uncertainty in the sensory predictions by manipulating the variance in exposed rotations. Results reveal that variance does not influence the final extent of adaptation but selectively impairs the retention of motor memories. These results suggest that a more uncertain forward model is more susceptible to change or decay.

Contribution of limb momentum to power transfer in athletic wheelchair pushing

Pushing capacity is a key parameter in athletic racing wheelchair performance. This study estimated the potential contribution of upper limb momentum to pushing. The question is relevant since it may affect the training strategy adopted by an athlete. A muscle-free Lagrangian dynamic model of the upper limb segments was developed and theoretical predictions of power transfer to the wheelchair were computed during the push phase. Results show that limb momentum capacity for pushing can be in the order of 40J per push cycle at 10m/s, but it varies with the specific pushing range chosen by the athlete. Although use of momentum could certainly help an athlete improve performance, quantifying the actual contribution of limb momentum to pushing is not trivial. A preliminary experimental investigation on an ergometer, along with a simplified model of the upper limb, suggests that momentum is not the sole contributor to power transfer to a wheelchair. Muscles substantially contribute to pushing, even at high speeds. Moreover, an optimal pushing range is challenging to find since it most likely differs if an athlete chooses a limb momentum pushing strategy versus a muscular exertion pushing strategy, or both at the same time. The study emphasizes the importance of controlling pushing range, although one should optimize it while also taking the dynamics of the recovery period into account.