Grant A. Handrigan

Weight loss and muscular strength affect static balance control

Objective:Overweight individuals sway more than normal weight individuals. Major weight loss improves their balance control despite a related decrease in muscle strength. Presumably, muscular strength is an important factor for balance control. This study investigated the effect that a change in body mass has on relative strength and balance control.Methodology:Force (isometric knee extension) and balance control (center of pressure speed and range) were studied in three groups; normal weight (BMI <25 kg m−2), obese (30 kg m−2 <BMI< 40 kg m−2) and excess obese (BMI >40 kg m−2) Caucasian male individuals.Results:The excess obese individuals who underwent bariatric surgery as a weight loss strategy were studied before, 3 and 12 months after losing on average, 66.9 kg (±95% CI 55.8, 77.9 kg; on average, 45% of their weight). The obese individuals who underwent diet modifications were studied before dieting and when resistance to weight loss occurred after losing on average 11.7 kg (±95% CI 9.3, 14.2 kg; on average, 12% of their weight). The control group was studied twice, 50 weeks apart. In obese and excess obese individuals, losing weight reduced absolute knee muscular strength on average, by 8.2 kg (±95% CI 3.9, 12.5 kg; on average, 10% of their strength) and 23.9 kg (±95% CI 12.1, 35.8 kg; on average, 33% of their strength). However, it also increased balance control measured with speed of the center of foot pressure, on average, by 0.10 cm s–1 (±95% CI 0.05, 0.14 cm s–1; or increased of 12%) and 0.28 cm s–1 (±95% CI 0.07, 0.47 cm s–1; increased of 27%), respectively. Relative strength increased approximately by 22% for only the excess obese group 12 months post surgery.Conclusion:This suggests, in overweight individuals, weight loss is more efficient at improving balance control than increasing, or even maintaining muscle strength. In these individuals, training programs aimed at improving balance control should primarily target weight loss.

Short term alteration of balance control after a reduction of plantar mechanoreceptor sensation through cooling.

Proprioceptive inputs from the plantar sole contribute to balance control during normal quiet standing. This study investigated the cooling of plantar sole mechanoreceptors through ice immersion and its effects on balance control and lower leg muscle activity. Ten healthy males participated in this study. Plantar sole sensitivity was tested using the two point discriminatory test and the Von Frey monofilaments test. Plantar sole cooling was achieved through foot immersion in ice water. Balance control was measured using a force platform with seven trials (30s) performed before and after ice water foot immersion. Lower limb balance control muscle activity was measured with electromyography. Ice cooling reduced the plantar sole sensitivity of the foot. A short term alteration in balance control was observed with only the first trial showing significantly greater speed and RMS of the velocity of the centre of pressure in the cooling condition when compared to control trials before cooling. Muscular activity increased following the first trial. The adaptation observed after the short term alteration of balance control, could result from sensory reweighting processes. It is suggested that the muscular activity increase is evidence of sensory reweighting and contributes to the regulation of balance control when the plantar sole sensation is partially inhibited.

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.

Obesity Alters Balance and Movement Control

Epidemic excess of weight is considered as a critical and common health problem. It is associated with many physiological and psychological disorders. Other than metabolic problems, obesity also affects the efficient execution of daily living activities such as the simple act of standing, walking or grabbing an object while standing. This article aims at presenting a state of knowledge of recent studies illustrating the detrimental effect of obesity and the beneficial effect of weight loss on postural stability and on the speed and accuracy of upper-limb goal-directed movements performed from a standing posture. Evidence supporting the suggestion that greater strength and training, at least for standing conditions, do not overcome the functional limitations imposed by obesity are presented. It is suggested that obese individuals may suffer from a reduced plantar sole sensitivity. As a conclusion to this work, we confirm the deleterious effect of overweight on motor control as weight loss translates into an improved balance control and upper limb speed-accuracy performance when standing.

Reduced plantar sole sensitivity induces balance control modifications to compensate ankle tendon vibration and vision deprivation.

The aim of this study was to investigate if sensory reweighting occurred to control balance when the sensitivity of the plantar sole is reduced using cooling. To address this question, visual information was manipulated and/or ankle proprioception was altered by Achilles tendon vibration. It was expected that Achilles tendon vibration and vision deprivation would induce greater center of pressure (CoP) excursions and/or increase of electromyographic (EMG) activity of the ankle muscles (triceps surea and tibialis anterior) with than without cooling of the plantar sole. To verify these hypotheses, the CoP and EMG activity of the ankle muscles were simultaneously recorded during quiet standing trials of 30s before and after feet cooling procedure. Results showed that plantar sole sensitivity alteration did not lead to larger CoP excursions even during Achilles tendon vibration in absence of vision. This could be explained by an increase in the EMG activity of the triceps surae after the cooling procedure without modification of tibialis anterior EMG activity. This study suggests that to compensate alteration in plantar sole sensitivity, the central nervous system increased the muscular activity of the triceps surae to limit CoP excursions.

Childhood obesity affects postural control and aiming performance during an upper limb movement

Obesity reduces the efficiency of postural and movement control mechanisms. However, the effects of obesity on a functional motor task and postural control in standing and seated position have not been closely quantified among children. The aim of this study is to examine the effects of obesity on the execution of aiming tasks performed in standing and seated conditions in children. Twelve healthy weight children and eleven obese children aged between 8 and 11 years pointed to a target in standing and seated position. The difficulty of the aiming task was varied by using 2 target sizes (1.0 cm and 5.0 cm width; pointing to the smaller target size needs a more precise movement and constitutes a more difficult task). Hand movement time (MT) and its phases were measured to quantify the aiming task. Mean speed of the center of pressure displacement (COP speed) was calculated to assess postural stability during the movement. Obese children had significantly higher MTs compared to healthy-weight children in seated and standing conditions explained by greater durations of deceleration phase when aiming. Concerning the COP speed during the movement, obese children showed significantly higher values when standing compared to healthy-weight children. This was also observed in the seated position. In conclusion, obesity adds a postural constraint during an aiming task in both seated and standing conditions and requires obese children to take more time to correct their movements due to a greater postural instability of the body when pointing to a target with the upper-limb.

Biomechanical differences between obese and healthy-weight workers in manual materials handling

The objective of this study was to evaluate the work strategies of obese and healthy-weight workers in manual materials handling. Seventeen obese and 20 healthy-weight manual materials handlers participated in this laboratory study. The tasks consisted of transferring four boxes between a hand trolley and a conveyor. The weight of the box (15 vs. 23 kg), the handling height and the working configuration were modified to see what impact these changes had on the participants’ manual materials handling. Biomechanical measures included net moments, expressed in the pelvic system (flexion–extension, lateral bending and torsion moments), kinematics of body segments and box displacements. The results indicated that trunk and knee postures and horizontal hand distances from L5/S1 were not significantly different between the two groups. Peak moments of force around the transverse, sagittal and longitudinal axes at L5/S1 were 13.3% to 59.0% higher during box lifting and lowering for the obese than for the non-obese workers. The individuals’ body weight explained 57% of the variability in the maximal transverse moments of force at L5/S1 during the lifting of the boxes from the ground. These results suggest that the extra mass of an obese worker causes additional stress for the musculoskeletal structures of the back. These biomechanical differences potentially place obese workers at a greater risk of developing musculoskeletal problems during manual materials handling.

The effect of lower body cooling on the changes in three core temperature indices.

Rectal (T(re)), ear canal (T(ear)) and esophageal (T(es)) temperatures have been used in the literature as core temperature indices in humans. The aim of the study was to investigate if localized lower body cooling would have a different effect on each of these measurements. We hypothesized that prolonged lower body surface cooling will result in a localized cooling effect for the rectal temperature not reflected in the other core measurement sites. Twelve participants (mean ± SD; 26.8 ± 6.0 years; 82.6 ± 13.9 kg; 179 ± 10 cm, BSA = 2.00 ± 0.21 m(2)) attended one experimental session consisting of sitting on a rubberized raft floor surface suspended in 5 °C water in a thermoneutral air environment (approximately 21.5 ± 0.5 °C). Experimental conditions were (a) a baseline phase during which participants were seated for 15 min in an upright position on an insulated pad (1.408 K ⋅ m(2) ⋅ W(-1)); (b) a cooling phase during which participants were exposed to the cooling surface for 2 h, and (c) an insulation phase during which the baseline condition was repeated for 1 h. Temperature data were collected at 1 Hz, reduced to 1 min averages, and transformed from absolute values to a change in temperature from baseline (15 min average). Metabolic data were collected breath-by-breath and integrated over the same temperature epoch. Within the baseline phase no significant change was found between the three indices of core temperature. By the end of the cooling phase, T(re) was significantly lower (Δ = -1.0 ± 0.4 °C) from baseline values than from T(ear) (Δ = -0.3 ± 0.3 °C) and T(es) (Δ = -0.1 ± 0.3 °C). T(re) continued to decrease during the insulation phase from Δ -1.0 ± 0.4 °C to as low as Δ -1.4 ± 0.5 °C. By the end of the insulation phase T(re) had slightly risen back to Δ -1.3 ± 0.4 °C but remained significantly different from baseline values and from the other two core measures. Metabolic data showed no variation throughout the experiment. In conclusion, the local cooling of the buttock area results in a drop in rectal temperature compromising the validity of the rectal temperature as a core temperature index under these conditions.

Obesity, where is it driving us?

Obesity is recognized as an important issue that has an impact on several areas of our daily lives, such as driving. In the literature there exists an association between obesity and motor vehicle crashes. The goal of this article is to promote insightful reflection and discussion around this emerging topic. Searches were conducted on Pubmed. Search terms were “obesity” and “driving.” The literature was sorted into a summary of the general ideas and is presented for discussion. Relevant issues discussed include anthromechanical issues and car design, seat belt usage, and obesity-related health complications (ocular pathologies, diabetic complications, and obstructive sleep apnoea/hypopnea). Finally, though limited prevention strategies exist for these issues in the literature, some strategies are presented for consideration. With such a complex issue, there is no simple solution. Education is the first step, and with a comprehensive understanding of the risks, actions can be taken to prevent these issues.

Ventilatory response during an incremental exercise test: A mode of testing effect

Abstract This study compared ventilation patterns during incremental load tests to exhaustion. Ten endurance trained individuals and eight recreationally active trained individuals underwent a maximal oxygen uptake (O2max) determination test on both a cycle (CE) and treadmill (TM) ergometer. Cardiorespiratory variables O2,CO2, RER, E, and R), movement frequency (MF) and entrainment (ENT) were collected and calculated relative to fixed percentages of O2max (isometabolic), ranging from 60 to 100%. Minute ventilation ( E) was similar between groups on both ergometers. Concurrently, VT was significantly higher, while R was significantly lower on the CE compared to the TM in both groups (P<0.05). At isometabolic intensities there were no difference in R or ENT between groups or mode of testing while the endurance trained group reached higher VT values on the CE. Although the endurance trained group reached higher cardiorespiratory values compared to the recreationally active trained group, their ventilatory patterns were similar between modes of testing. These results seem to be dependent on the exercise modality and not necessarily the type of training individuals regularly participate in.