Postural stability in subjects with temporomandibular disorders and healthy controls: A comparative assessment

Purpose of the studyThe influence of the stomatognathic apparatus on body posture is a continuously discussed topic with contrasting results. The aim of this study is to analyze differences in postural stability between subjects with and without myogenous TMD.Methods25 subjects affected by myogenous TMD according with DC/TMD (6 males, 19 females; mean age 31.75 ± 6.68 years) and a healthy control group of 19 subjects (4 Males, 15 Females; mean age 27.26 ± 3.85 years) were enrolled in the study.Both groups underwent a posturo-stabilometric force platform exam under different mandibular and visual conditions. Sway area and sway velocity of the COP (Center Of foot Pressure) posturo-stabilometric parameters were evaluated and compared applying Mann-U-Whitney statistical test.ResultsThe sway area and sway velocity parameters resulted statistically significantly higher in the TMD group (sway area p < 0.01; sway velocity p < 0.05) in mandibular maximum intercuspation and rest positions with eyes open.ConclusionsThis study demonstrates a significant difference in body postural stability between subjects with myogenous TMD and healthy controls. In particular, sway area and sway velocity postural parameters are increased in these subjects.     

Characteristics of balance control in older persons who fall with injury – A prospective study

ObjectiveOlder adults who have recently fallen demonstrate increased postural sway compared with non-fallers. However, the differences in postural control between older adults who were seriously injured (SI) as a result of a fall, compared with those who fell but were not injured (NSI) and non-fallers (NFs), has not been investigated. The objective of the present study was to investigate the underlying postural control mechanisms related to injuries resulting from a fall.MethodsBoth traditional postural sway measures of foot center-of-pressure (CoP) displacements and fractal measures, the Stabilogram-Diffusion Analysis (SDA), were used to characterize the postural control. One hundred older adults aged 65–91 years were tested during narrow base upright stance in eyes closed condition; falls were monitored over a 1-year period.ResultsForty-nine older adults fell during the 1-year follow-up, 13 were seriously injured as a result of a fall (SI), 36 were not injured (NSI), and 49 were non-fallers (NFs); two passed away. The SDA showed significantly higher short-term diffusion coefficients and critical displacements in SI in the anterior–posterior direction compared with both NSI and NF. However, in the medio-lateral direction there were no statistically significant differences between groups. For the traditional measures of sway, the average anterior–posterior CoP range was also larger in SI individuals.ConclusionsThis work suggests that older fallers with a deterioration of anterior–posterior postural control may be at higher risk of serious injury following fall events.     

Feasibility and Inter-Rater Reliability of Physical Performance Measures in Acutely Admitted Older Medical Patients

ObjectivePhysical performance measures can be used to predict functional decline and increased dependency in older persons. However, few studies have assessed the feasibility or reliability of such measures in hospitalized older patients. Here we assessed the feasibility and inter-rater reliability of four simple measures of physical performance in acutely admitted older medical patients.DesignDuring the first 24 hours of hospitalization, the following were assessed twice by different raters in 52 (≥ 65 years) patients admitted for acute medical illness: isometric hand grip strength, 4-meter gait speed, 30-s chair stand and Cumulated Ambulation Score. Relative reliability was expressed as weighted kappa for the Cumulated Ambulation Score or as intra-class correlation coefficient (ICC_1,1) and lower limit of the 95%-confidence interval (LL_95%) for grip strength, gait speed, and 30-s chair stand. Absolute reliability was expressed as the standard error of measurement and the smallest real difference as a percentage of their respective means (SEM% and SRD%).ResultsThe primary reasons for admission of the 52 included patients were infectious disease and cardiovascular illness. The mean± SD age was 78±8.3 years, and 73.1% were women. All patients performed grip strength and Cumulated Ambulation Score testing, 81% performed the gait speed test, and 54% completed the 30-s chair stand test (46% were unable to rise without using the armrests). No systematic bias was found between first and second tests or between raters. The weighted kappa for the Cumulated Ambulation Score was 0.76 (0.60–0.92). The ICC1,1 values were as follows: grip strength, 0.95 (LL_95% 0.92); gait speed, 0.92 (LL_95% 0.73), and 30-s chair stand, 0.82 (LL_95% 0.67). The SEM% values for grip strength, gait speed, and 30-s chair stand were 8%, 7%, and 18%, and the SRD_95% values were 22%, 17%, and 49%.ConclusionIn acutely admitted older medical patients, grip strength, gait speed, and the Cumulated Ambulation Score measurements were feasible and showed high inter-rater reliability when administered by different raters. The feasibility and inter-rater reliability of the 30-s chair stand were moderate, complicating the use of the 30-s chair stand in acutely admitted older medical patients. However, the predefined modified version of the chair stand test was both feasible and with high inter-rater reliability in this population.     

The effects of early stages of aging on postural sway: A multiple domain balance assessment using a force platform

Technical advancements in instrumentation and analytical methods have improved the ability of assessing balance control. This study investigated the effects of early stages of aging on postural sway using traditional and contemporary postural indices from different domains. Eleven healthy young adults and fourteen healthy non-faller older adults performed two postural tasks: (a) functional limits of stability and (b) unperturbed bipedal stance for 120 s. Postural indices from spatial, temporal, frequency, and structural domains were extracted from the body’s center of pressure (COP) signals and its Rambling and Trembling components. Results revealed a preservation of functional limits of upright stability in older adults accompanied by larger, faster, and shakier body sway in both anterior-posterior and medio-lateral directions; increased medio-lateral sway frequency; increased irregularity of body sway pattern in time in both directions; and increased area, variability, velocity, and jerkiness of both rambling and trembling components of the COP displacement in the anterior-posterior direction (p < 0.02). Such changes might be interpreted as compensatory adjustments to the age-related decline of sensory, neural, and motor functions. In conclusion, balance assessment using postural indices from different domains extracted from the COP displacement was able to capture subtle effects of the natural process of aging on the mechanisms of postural control. Our findings suggest the use of such indices as potential markers for postural instability and fall risk in older adults.     

The Influence of Diabetic Peripheral Neuropathy on Local Postural Muscle and Central Sensory Feedback Balance Control

Poor balance control and increased fall risk have been reported in people with diabetic peripheral neuropathy (DPN). Traditional body sway measures are unable to describe underlying postural control mechanism. In the current study, we used stabilogram diffusion analysis to examine the mechanism under which balance is altered in DPN patients under local-control (postural muscle control) and central-control (postural control using sensory cueing). DPN patients and healthy age-matched adults over 55 years performed two 15-second Romberg balance trials. Center of gravity sway was measured using a motion tracker system based on wearable inertial sensors, and used to derive body sway and local/central control balance parameters. Eighteen DPN patients (age = 65.4±7.6 years; BMI = 29.3±5.3 kg/m²) and 18 age-matched healthy controls (age = 69.8±2.9; BMI = 27.0±4.1 kg/m²) with no major mobility disorder were recruited. The rate of sway within local-control was significantly higher in the DPN group by 49% (healthy local-control_slope = 1.23±1.06×10^-2 cm²/sec, P<0.01), which suggests a compromised local-control balance behavior in DPN patients. Unlike local-control, the rate of sway within central-control was 60% smaller in the DPN group (healthy central-control_slope-Log = 0.39±0.23, P<0.02), which suggests an adaptation mechanism to reduce the overall body sway in DPN patients. Interestingly, significant negative correlations were observed between central-control rate of sway with neuropathy severity (r _Pearson = 0.65-085, P<0.05) and the history of diabetes (r _Pearson = 0.58-071, P<0.05). Results suggest that in the lack of sensory feedback cueing, DPN participants were highly unstable compared to controls. However, as soon as they perceived the magnitude of sway using sensory feedback, they chose a high rigid postural control strategy, probably due to high concerns for fall, which may increase the energy cost during extended period of standing; the adaptation mechanism using sensory feedback depends on the level of neuropathy and the history of diabetes.     

Static Postural Stability in Women during and after Pregnancy: A Prospective Longitudinal Study

This longitudinal study aimed to compare static postural stability in women between early pregnancy, advanced pregnancy, and at 2 and 6 months postpartum. Forty-five pregnant women were enrolled and 31 completed the protocol. Data were collected at 7–16 and 34–39 weeks gestation, and at 6–10 and 26–30 weeks postpartum. For each subject, the center of foot pressure path length and mean velocity (with directional subcomponents) were computed from 30-s long quiet-standing trials on a stationary force plate with eyes open or closed. The body mass, stance width, and sleep duration within 24 h before testing were also recorded. Static postural stability was not different between pregnancy and postpartum, except for the anterior posterior sway tested in the eyes-closed condition, which was significantly increased in late pregnancy compared to that at 2 and 6 months postpartum. Pregnant/postpartum women’s body mass weakly positively correlated with anterior-posterior sway in the eyes-closed condition and their stance width weakly positively correlated with the anterior-posterior sway in the eyes-open condition. No effect of sleep duration on postural sway was found. Our findings indicate that under visual deprivation conditions women in advanced pregnancy may have decreased static stability compared to their non-pregnant state.     

The effect of plantar flexor muscle fatigue on postural control

Objective

Previous studies have demonstrated that ankle muscle fatigue alters postural sway. Our aim was to better understand postural control mechanisms during upright stance following plantar flexor fatigue.

Method

Ten healthy young volunteers, 25.7 ± 2.2 years old, were recruited. Foot center-of-pressure (CoP) displacement data were collected during narrow base upright stance and eyes closed (i.e. blindfolded) conditions. Subjects were instructed to stand upright and as still as possible on a force platform under five test conditions: (1) non-fatigue standing on firm surface; (2) non-fatigue standing on foam; (3) ankle plantar flexor fatigue, standing on firm surface; (4) ankle plantar flexor fatigue, standing on foam; and (5) upper limb fatigue, standing on firm surface. An average of the ten 30-s trials in each of five test conditions was calculated to assess the mean differences between the trials. Traditional measures of postural stability and stabilogram-diffusion analysis (SDA) parameters were analyzed.

Results

Traditional center of pressure parameters were affected by plantar flexor fatigue, especially in the AP direction. For the SDA parameters, plantar flexor fatigue caused significantly higher short-term diffusion coefficients, and critical displacement in both mediolateral (ML) and anteroposterior (AP) directions. Long-term postural sway was different only in the AP direction.

Conclusions

Localized plantar flexor fatigue caused impairment to postural control mainly in the Sagittal plane. The findings indicate that postural corrections, on average, occurred at a higher threshold of sway during plantar flexor fatigue compared to non-fatigue conditions.     

Relationship between Spectral Characteristics of Spontaneous Postural Sway and Motion Sickness Susceptibility

Motion sickness (MS) usually occurs for a narrow band of frequencies of the imposed oscillation. It happens that this frequency band is close to that which are spontaneously produced by postural sway during natural stance. This study examined the relationship between reported susceptibility to motion sickness and postural control. The hypothesis is that the level of MS can be inferred from the shape of the Power Spectral Density (PSD) profile of spontaneous sway, as measured by the displacement of the center of mass during stationary, upright stance. In Experiment 1, postural fluctuations while standing quietly were related to MS history for inertial motion. In Experiment 2, postural stability measures registered before the onset of a visual roll movement were related to MS symptoms following the visual stimulation. Study of spectral characteristics in postural control showed differences in the distribution of energy along the power spectrum of the antero-posterior sway signal. Participants with MS history provoked by exposure to inertial motion showed a stronger contribution of the high frequency components of the sway signal. When MS was visually triggered, sick participants showed more postural sway in the low frequency range. The results suggest that subject-specific PSD details may be a predictor of the MS level. Furthermore, the analysis of the sway frequency spectrum provided insight into the intersubject differences in the use of postural control subsystems. The relationship observed between MS susceptibility and spontaneous posture is discussed in terms of postural sensory weighting and in relation to the nature of the provocative stimulus.     

The influence of adipose tissue location on postural control

A growing body of evidence suggests, that excessive body weight is inseparably connected with postural instability. In none of previous studies, body weight distribution has been considered as a factor, which may affect results of a static posturography. The purpose of the present study is to quantify some center of foot pressure (COP) characteristics in 40 obese women with android type of obesity (waist-to-hip ratio - WHR ≥ 0.85, BMI: 37.5 ± 5.4) and 40 obese women with gynoid type of obesity (WHR < 0.85, BMI: 36.9 ± 5.1). Variables of postural sway were acquired while subjects were standing quietly on a force plate with eyes open and closed. Both in the sagittal and frontal plane sway range, average velocity, and maximal velocity of COP were calculated. Moreover, the total average velocity and total maximal velocity of the COP displacement were computed.Women with abdominal obesity showed a larger sway range in the anterior-posterior plane with eyes open (p < 0.0282) and eyes closed conditions (p < 0.0115) and a greater maximal COP velocity to compare with subjects with gynoidal obese type (p < 0.0112) with eyes closed condition.The postural stability in obese women from the biomechanical point of view is strongly dependent on body distribution. Women with the abdominal obesity type may be exposed to a greater risk of postural instability as compare to women with gynoid fat distribution.     

Dynamic postural stability during advancing pregnancy

Pregnant women are at an increased risk of experiencing a fall. Numerous anatomical, physiological, and hormonal alterations occur during pregnancy, but the influence of these factors on dynamic postural stability has not been explored. The purpose of this study was to examine dynamic postural stability in pregnant women during their second and third trimesters as well as in a group of non-pregnant control women.MethodsEighty-one women (41 pregnant, 40 controls) participated stood on a force plate that translated anteroposteriorly at small, medium, and large magnitudes. Reaction time and center of pressure (COP) movement during the translations were analyzed. Trimester, perturbation direction, and perturbation magnitude were the independent variables in a mixed-model analysis of variance on each of the following dependent variables: reaction time, initial sway, total sway, and sway velocity.ResultsReaction time to the perturbation was not significantly different between the groups. Initial sway, total sway, and sway velocity were significantly less during the third trimester than during the second trimester and when compared to the non-pregnant controls (P<0.05). No differences were found in any of the measures between the pregnant women in their second trimesters and the control group.ConclusionAlterations in sway responses to perturbations are seen in the third trimester in healthy women with uncomplicated pregnancies. Further study is needed to examine the biomechanical and physiological reasons behind this altered dynamic postural stability.     

Serum 25-hydroxyvitamin D levels are not associated with impaired postural sway in community-dwelling older women: a 6-year follow-up study

Objectives:A positive association between levels of blood 25-hydroxyvitamin D (25[OH]D), an index of vitamin D status, and physical balance has been reported from cross-sectional studies, but longitudinal studies are rare. The present study aimed to test the hypothesis that low serum 25(OH)D levels are longitudinally associated with impaired postural sway over a 6-year follow-up period in older women.Methods:The present cohort consisted of 392 community-dwelling Japanese women aged ≥69 years. Baseline examinations included serum 25(OH)D and physical performance tests, including postural sway velocity. Standing postural sway was evaluated by measuring gravity-center sway velocity. Follow-up physical performance tests were conducted 6 years later.Results:Mean subject age and serum 25(OH)D levels were 73.3 years (SD 3.7) and 61.0 nmol/L (SD 16.9), respectively. No significant association was found between 25(OH)D levels and changes in postural sway velocity (adjusted P for trend=0.72). Women with 25(OH)D <30 nmol/L tended to have lower Δpostural sway velocity than those with 25(OH)D ≥30 nmol/L (mean, -0.59 vs 0.37 cm/s, respectively; adjusted P=0.13).Conclusions:Vitamin D levels are not longitudinally associated with impaired postural sway in older women. Further longitudinal studies are needed to corroborate the results of this study.     

Reciprocal influences on performances of a postural–suprapostural task by manipulating the level of task-load

The objective of this study was to investigate the reciprocal influences of stance pattern (bilateral stance vs. unilateral stance) and thumb-index precision grip task (static target vs. dynamic target) on postural–suprapostural tasks by manipulating task-load. Fifteen healthy volunteers participated in four postural–suprapostural tasks, including static force-matching in bilateral/unilateral stance (BS_static; US_static), dynamic force-matching in bilateral/unilateral stance (BS_dynamic; US_dynamic), and two control tasks in bilateral and unilateral stances without a finger task. The normalized force error (NFE), reaction time (RT) of the finger tasks, and normalized change in center of pressure sway (ΔNCoP) were measured. For suprapostural task performance, a significant interaction effect between postural and suprapostural tasks on NFE of the finger tasks was noted (static: BS < US; dynamic: BS > US), but RT was not different among the four tasks. For postural task performance, negative ΔNCoP during unilateral stance indicated a spontaneous reduction in postural sway due to added force-matching. In contrast, addition of force-matching tended to increase postural sway during bilateral stance, but postural fluctuations decreased as task-load of suprapostural task increased (BS_dynamic < BS_static). In conclusion, performance of postural–suprapostural tasks was differently modulated by task-load increment. Our observations favored adaptive resource-sharing and implicit expansion of resource capacity for a postural task with a motor suprapostural goal.     

Intersession reliability of a posturo-stabilometric test,using a force platform

Aim of the studyTo evaluate the intersession reliability of a posturo-stabilometric examination.MethodsSingle blind clinical trial conducted in two sessions over two weeks.44 healthy volunteers free from postural and temporomandibular disorders. All the subjects complied with the criteria for completing the study.All the subjects underwent two sessions of posturo-stabilometric examinations in different visual and mandibular conditions.Sway area, sway length and the coordinates of the center of pressure were evaluated and statistically analyzed using the Intraclass correlation coefficient (ICC).ResultsAll the posturo-stabilometric parameters seemed to have an excellent reproducibility with overall ICCs higher than 70% and good confidence intervals except for the sway area (ICC 0.422 with CI 0.283–0.560 with open eyes and ICC 0.554 with CI 0.424–0.683 with closed eyes).ConclusionsThe posturo-stabilometric examination carried out using a force platform has a good intrasession and intersession reliability, especially considering sway velocity, COP X and COP Y parameters. The force platform usefulness in analyzing static posture is confirmed in any medical field.     

Modelling 3D control of upright stance using an optimal control strategy

A 3D balance control model of quiet upright stance is presented, based on an optimal control strategy, and evaluated in terms of its ability to simulate postural sway in both the anterior-posterior and medial-lateral directions. The human body was represented as a two-segment inverted pendulum. Several assumptions were made to linearise body dynamics, for example, that there was no transverse rotation during upright stance. The neural controller was presumed to be an optimal controller that generates ankle control torque and hip control torque according to certain performance criteria. An optimisation procedure was used to determine the values of unspecified model parameters including random disturbance gains and sensory delay times. This model was used to simulate postural sway behaviours characterised by centre-of-pressure (COP)-based measures. Confidence intervals for all normalised COP-based measures contained unity, indicating no significant differences between any of the simulated COP-based measures and corresponding experimental references. In addition, mean normalised errors for the traditional measures were 相似文献   

Suitability of Kinect for measuring whole body movement patterns during exergaming

Exergames provide a challenging opportunity for home-based training and evaluation of postural control in the elderly population, but affordable sensor technology and algorithms for assessment of whole body movement patterns in the home environment are yet to be developed. The aim of the present study was to evaluate the use of Kinect, a commonly available video game sensor, for capturing and analyzing whole body movement patterns. Healthy adults (n=20) played a weight shifting exergame under five different conditions with varying amplitudes and speed of sway movement, while 3D positions of ten body segments were recorded in the frontal plane using Kinect and a Vicon 3D camera system. Principal Component Analysis (PCA) was used to extract and compare movement patterns and the variance in individual body segment positions explained by these patterns. Using the identified patterns, balance outcome measures based on spatiotemporal sway characteristics were computed. The results showed that both Vicon and Kinect capture >90% variance of all body segment movements within three PCs. Kinect-derived movement patterns were found to explain variance in trunk movements accurately, yet explained variance in hand and foot segments was underestimated and overestimated respectively by as much as 30%. Differences between both systems with respect to balance outcome measures range 0.3–64.3%. The results imply that Kinect provides the unique possibility of quantifying balance ability while performing complex tasks in an exergame environment.     

Translation of Questionnaires Measuring Health Related Quality of Life Is Not Standardized: A Literature Based Research Study

IntroductionThere is growing awareness of the need to explore patient reported outcomes in clinical trials. In the Scandinavian Surgical Outcomes Research Group we are conducting several clinical trials in cooperation between Danish and Swedish surgical researchers, and we use questionnaires aimed at patients from both countries. In relation to this and similar international cooperation, the validity and reliability of translated questionnaires are central aspects.ResultsWe retrieved 187 studies and out of theses we included 52 studies. The psychometric properties of the translated versions were validated using different tests. The focus was on internal validity (96%), reliability (67%) criterion validity (81%), and construct validity (62%). For internal validity Cronbach''s alpha was used in 94% of the studies.ConclusionsThis study shows that there seems to be a consensus regarding the translation process (especially for internal validity) although most researchers did not use a translation guide. Moreover, we recommended that clinical researchers should consider three steps covering the process of translation, the qualitative validation as well as the quantitative validation.     

Modelling 3D control of upright stance using an optimal control strategy

A 3D balance control model of quiet upright stance is presented, based on an optimal control strategy, and evaluated in terms of its ability to simulate postural sway in both the anterior–posterior and medial–lateral directions. The human body was represented as a two-segment inverted pendulum. Several assumptions were made to linearise body dynamics, for example, that there was no transverse rotation during upright stance. The neural controller was presumed to be an optimal controller that generates ankle control torque and hip control torque according to certain performance criteria. An optimisation procedure was used to determine the values of unspecified model parameters including random disturbance gains and sensory delay times. This model was used to simulate postural sway behaviours characterised by centre-of-pressure (COP)-based measures. Confidence intervals for all normalised COP-based measures contained unity, indicating no significant differences between any of the simulated COP-based measures and corresponding experimental references. In addition, mean normalised errors for the traditional measures were < 8%, and those for most statistical mechanics measures were ～3–66%. On the basis these results, the proposed 3D balance control model appears to have the ability to accurately simulate 3D postural sway behaviours.     

Effect of 14 days of bed rest in older adults on parameters of the body sway and on the local ankle function

This study explored the effects of a 14-day horizontal bed rest (BR) without countermeasures on postural sway, maximal voluntary torque and precision of voluntary torque matching. Sixteen subjects were tested before, immediately after and two weeks after BR. The increase in frequency and amplitude after BR was comparable for both sway subcomponents (rambling and trembling) in medial-lateral direction. But in anterior–posterior direction, rambling increased more in frequency (?7% vs. +31%, p < 0.05) while trembling increased more in amplitude (+35% vs. +84%, p < 0.05). The drop in maximal voluntary torque after BR was present for plantar flexion (p < 0.05) but not for dorsal flexion. After the BR, the subjects were less precise in the dorsal flexion torque matching task (p < 0.05). All the observed parameters, except the dorsal flexion torque matching error, returned back to the pre-BR values after the two weeks of re-conditioning. Results of this study indicate that body sway subcomponents responded differently to BR. Based on these findings, it was not possible to draw clear assumptions on the effects of neural and structural changes on body sway.     

The effect of a maternity support belt on static stability and posture in pregnant and non-pregnant women

PurposePhysical and hormonal changes during pregnancy are thought to affect balance and injury risk, with increased numbers of falls being reported. A maternity support belt (MSB) has been suggested to stabilize the pelvis and to enhance balance. The purpose of this study was therefore to investigate the effect of an MSB on postural stability in different trimesters of pregnancy.MethodsPostural stability was assessed in the first (T1, n = 30), second (T2, n = 30) and third trimester (T3, n = 30) of pregnancy and compared to non-pregnant controls (n = 30), using a portable force plate. Postural sway during quiescent standing with and without applying an MSB was characterized by analyzing path length, velocity, amplitudes and area. Subsequently, anterior and posterior limits of stability (LoS) were determined.ResultsPostural sway during quiescent standing did not change with pregnancy. However, LoS performance was reduced already in T1, before body mass significantly increased. The MSB led to a small improvement in the LoS while slightly increasing postural sway in anterior-posterior direction and shifting the center of pressure posteriorly during quiescent standing.ConclusionWhile impairments in balance already occurred early in pregnancy before body mass significantly increased, they were subtle and only measurable in exacerbated conditions. This challenges the assumed necessity of balance enhancing interventions in pregnant women. Although the MSB significantly affected body posture, the magnitude of the LoS improvement using the MSB was very small. Thus, it remains debatable if the MSB is a meaningful tool to increase balance during pregnancy.     

The comparison of trunk muscles EMG activation between subjects with and without chronic low back pain during flexion-extension and lateral bending tasks.

The purpose of the study was to compare the electromyographic (EMG) activity of the trunk muscles between normal subjects and chronic low back pain (CLBP) patients during standardized trunk movements. Thirty-three male subjects (18 normals, 15 suffering from non specific CLBP) aged between 35 and 45 yr participated. A biomechanical analysis involving the recording of EMG signals from 12 trunk muscles, the kinematics of trunk segments and the computation of L5/S1 moments was performed. The subjects performed flexion-extension and lateral bending (left and right) tasks (three complete cycles) with and without a 12 kg load. Between group comparisons were performed on the full cycle average pattern of all biomechanical variables for each task. The reliability of EMG variables was evaluated for 10 subjects (5 normals and 5 CLBP) who performed the tasks on three different days. The reliability of EMG amplitude values was generally excellent for agonist muscles but poor to moderate for antagonists. The EMG amplitude analysis revealed significant differences between groups for some muscles (left lumbar and thoracic erector spinae). The abnormal (asymmetric) EMG patterns detected among CLBP patients were not explained by postural asymmetries.