Functional postural responses after perturbations in multiple directions in a standing man: a principle of decoupled control

The objective of this study was to assess functional postural responses by analyzing the net joint torques (NJT) in the ankles and the hips resulting from perturbations delivered in multiple directions to subjects standing quietly. A total of eight subjects were standing on two force platforms while an apparatus randomly delivered controlled perturbations at the level of the pelvis in eight directions: anterio-posterior (AP), medio-lateral (ML), and four combinations of these principal directions. Perturbations were repeated five times in each direction for six conditions (i.e., three different perturbation strengths and three different feet orientations). The comparison of the averaged ankle sum NJT (AP) responses showed that the time courses of the responses elicited by a perturbation acting only in the AP direction were identical to those elicited by a combination of two corresponding AP and ML perturbations. In contrast the observed averaged ankle NJT (ML) responses did not follow the same similarity. The comparison of the averaged ankle and hip sum NJT (ML) responses revealed that the time courses of the responses elicited by a perturbation acting only in the ML direction were identical to those elicited by a combination of two corresponding AP and ML perturbations. These findings were invariable of the experimental conditions and were consistent among all the eight subjects. Thereby, we conclude that the ankle sum NJT (AP) and the ankle and hip sum NJT (ML) are the global variables being controlled. This shows that CNS controls the recovery from the multiple direction perturbations of moderate strength by decoupling the AP-ML postural space into two orthogonal directions (AP and ML).     

Posture-dependent trunk extensor EMG activity during maximum isometrics exertions in normal male and female subjects.

Posture-dependent trunk function data are important for appropriate normalization of submaximal trunk exertions, and is also necessary to define a more precise and specific use for strength testing in the prevention and diagnosis of spinal disorders. The aim of the current study was to quantify maximal effort trunk muscle extensor activity and trunk isometric extension torque over a functional range of sagittal standing postures. Twenty healthy, young adult male and female subjects performed isometric extension tasks over a sagittal posture range of -20 degrees extension to +50 degrees flexion, in 10 degrees increments. Erector spinae muscle activity was recorded bilaterally at the level of L3 using surface EMG electrodes. Isometric trunk extension torque was measured using a trunk dynamometer. EMG and trunk torque differed significantly between genders, but there were no differences between male and female subjects when the data were normalized with respect to the upright posture. For the combined male and female population, upright posture normalized L3 EMG activity (EMGn) and trunk extension torque (Tn) increased 1.7-fold and 3.5-fold, respectively, over the 70 degrees range of sagittal postures examined. The ratio (Tn/EMGn) increased two-fold (0.83 to 1.67) from -20 degrees extension to +50 degrees flexion, indicating that the neuromuscular efficiency increases with flexion. Trunk extension torque normalized with respect to the upright posture was linearly and positively correlated (r = 0.59, P < 0.001) to similarly normalized L3 EMG activity. This relatively weak correlation suggests that trunk muscle synergism and/or intrinsic muscle length-tension relationships are also modulated by posture. This study provides data that can be used to estimate trunk extensor muscle function over a broad range of sagittal postures. Our findings indicate that appropriate postural normalization of trunk extensor EMG activity is necessary for studies where submaximal trunk exertions are performed over a range of upright postures.     

Inter-joint coordination of posture on a seesaw device

Even though specific adjustments of the multi-joint control of posture have been observed when posture is challenged, multi-joint coordination on a seesaw device has never been accurately assessed. The current study was conducted in order to investigate the multi-joint coordination when subjects were standing on either a seesaw device or on a stable surface, with the eyes open or closed. Eighteen healthy active subjects were recruited. A principal component analysis and a Self-Organizing Maps analysis were performed on the joint angles in order to detect and characterize dominant coordination patterns. Intermuscular EMG coherence was analysed in order to assess the neurophysiological mechanisms associated with these coordination patterns. The results illustrated a multi-joint organization of posture on both stable ground and on the seesaw, with a higher variability among the individual postural responses observed when standing on the seesaw. These findings challenge the classical assumption of ankle mechanisms as dominating control on seesaw devices and confirm that inter-joint coordination in postural control is strongly modulated by stance conditions. When standing on the seesaw without vision, a decrease in intermuscular coherence was observed without any impact on the joint coordination patterns, likely due to an increase dependence on proprioceptive information.     

Neural control of quadrupedal and bipedal stance: implications for the evolution of erect posture

The transition among hominids from quadrupedalism to bipedalism resulted in modifications in their musculoskeletal morphology. It is unclear, however, whether changes in the circuitry of the CNS were also necessary in order to accommodate the unique balance requirements of two-limb support. This study addresses the issue of modifications in control strategies by investigating the rapid, automatic postural responses of feline and human subjects to sudden disturbances of balance in the anteroposterior (AP) direction while they stand quadrupedally and bipedally on movable platforms. Postural responses are characterized in terms of segmental adjustments, generated AP shear forces, and electromyographic activity. Feline and human subjects correct posture similarly when standing quadrupedally. Furthermore, both species correct stance primarily with their hindlimbs and use their forelimbs as supportive struts. In contrast, both species use completely different correctional strategies when standing bipedally. Morphological restrictions, however, prevent cats from adopting the pillar-like plantigrade posture of human beings. Thus, the correctional strategies of bipedal cats are distinct from those of bipedal human subjects. It is concluded that 1) automatic postural response patterns of quadrupedal Felis and bipedal Homo reflect the different biomechanical characteristics of the initial postures rather than species differences in CNS circuitry controlling stance; 2) hindlimb-dominated posture control is probably a common and relatively ancient pattern; and 3) reorganization of hominid CNS circuitry was probably unnecessary because hindlimb control was already a feature of the system.     

Stooping,crouching, and standing – Characterizing balance control strategies across postures

BackgroundWhile stooping and crouching postures are critical for many activities of daily living, little is known about the balance control mechanisms employed during these postures. Accordingly, the purpose of this study was to characterize the mechanisms driving net center of pressure (COP_Net) movement across three postures (standing, stooping, and crouching) and to investigate if control in each posture was influenced by time.MethodsTen young adults performed the three postures for 60 s each. Kinetic signals were collected via a force platform under each foot. To quantify mechanisms of control, correlations (Correl_LR) were calculated between the left and right COP trajectories in the anterior-posterior (AP) and medio-lateral (ML) directions. To examine the potential effects of time on balance control strategies, outcomes during the first 30 s were compared to the last 30 s.ResultsCorrel_LR values did not differ across postures (AP: p = 0.395; ML: p = 0.647). Further, there were no main effects of time on Correl_LR (AP: p = 0.976; ML: p = 0.105). A significant posture-time interaction was observed in the ML direction (p = 0.045) characterized by 35% decreases in Correl_LR over time for stooping (p = 0.022).ConclusionThe dominant controllers of sway (i.e., AP: ankle plantar/dorsi flexors; ML: hip load/unload mechanism) are similar across quiet stance stooping, and crouching. Changes in ML control strategies over time suggests that fatigue could affect prolonged stooping more so than crouching or standing.     

Time-to-boundary measures of postural control during single leg quiet standing

A novel approach to quantifying postural stability in single leg stance is assessment of time-to-boundary (TTB) of center of pressure (COP) excursions. TTB measures estimate the time required for the COP to reach the boundary of the base of support if it were to continue on its instantaneous trajectory and velocity, thus quantifying the spatiotemporal characteristics of postural control. Our purposes were to examine: (a) the intrasession reliability of TTB and traditional COP-based measures of postural control, and (b) the correlations between these measures. Twenty-four young women completed three 10-second trials of single-limb quiet standing on each limb. Traditional measures included mean velocity, standard deviation, and range of mediolateral (ML) and anterior-posterior (AP) COP excursions. TTB variables were the absolute minimum, mean of minimum samples, and standard deviation of minimum samples in the ML and AP directions. The intrasession reliability of TTB measures was comparable to traditional COP based measures. Correlations between TTB and traditional COP based measures were weaker than those within each category of measures, indicating that TTB measures capture different aspects of postural control than traditional measures. TTB measures provide a unique method of assessing spatiotemporal characteristics of postural control during single limb stance.     

Center of pressure and center of mass behavior during gait initiation on inclined surfaces: A statistical parametric mapping analysis

This study analyzed gait initiation (GI) on inclined surfaces with 68 young adult subjects of both sexes. Ground reaction forces and moments were collected using two AMTI force platforms, of which one was in a horizontal position and the other was inclined by 8% in relation to the horizontal plane. Departing from a standing position, each participant executed three trials in the following conditions: horizontal position (HOR), inclined position at ankle dorsi-flexion (UP), and inclined position at ankle plantar-flexion (DOWN). Statistical parametric mapping analysis was performed over the entire center of pressure (COP) and center of mass (COM) time series. COP excursion did not show significant differences in the medial-lateral (ML) direction in both inclined conditions, but it was greater in the anterior-posterior (AP) direction for both inclined conditions. COP velocities are smaller in discrete portions of GI for the UP and DOWN conditions. COM displacement was greater in the ML direction during anticipatory postural adjustments (APA) in the UP condition, and COM moves faster in the ML direction during APA in the UP condition but slower at the end of GI for both the UP and the DOWN conditions. The COP-COM vector showed a greater angle in the DOWN condition. We observed changes for COP and COM in GI in both the UP and the DOWN conditions, with the latter showing changes for a great extent of the task. Both the UP and the DOWN conditions showed increased COM displacement and velocity. The predominant characteristic during GI on inclined surfaces, including APA, appears to be the displacement of the COM.     

Gender‐specific Effect of Obesity on Balance

Obesity modifies the body geometry by adding mass to different regions and it influences the biomechanics of activities of daily living. Weight influences postural stability, but there is no consensus as to whether the different fat distribution in males and females produces gender‐related effects on balance. The aim of this study was to investigate the effect of body weight increases on postural performance in males and females. A total of 22 obese females (BMI: 41.1 ± 4.1 kg/m²) and 22 obese males (BMI: 40.2 ± 5 kg/m²) were analyzed during a static posture trial on a force platform in standardized conditions. Twenty healthy subjects (10 females, 10 males) constituted the control group. We computed the following parameters related to the center of pressure (CoP): velocity and displacements along the antero‐posterior (AP) and medio‐lateral axis (ML). We found several statistically significant differences between healthy and obese men, in particular regarding the AP and ML CoP parameters, which were correlated to body weight (r = 0.36–0.58). The comparison between healthy and obese females pointed out statistically significant differences in AP parameters and no significant differences in ML displacements. Body weight was found to correlate with AP parameters (r = 0.36–0.74), but not with ML displacements. The increased body mass seems to produce AP instability in both genders and ML destabilization only in males. Rehabilitation programs should take these findings into account by adopting specific interventions to improve ML control in obese males, and through weight loss and strengthening of ankle flexors/extensors in both genders.     

Unilateral lower limb muscle fatigue induces bilateral effects on undisturbed stance and muscle EMG activities

The study investigated the effects of an unilateral ankle muscle fatigue onto independent postural control parameters including the trajectories of the estimated resultant CoP (CoPres) and his components: the centre of gravity (CG) and CoP–CG trajectories.Nine healthy men realized series of 10 toe-lift immediately followed by 10 knee flexions until exhaustion with one (Ex) leg. Maximal isometric voluntary contractions, postural sway measures of each leg, and muscular activities of the ankle muscles were recorded before and immediately after the fatiguing exercise.As expected, the latter induced a decrease in maximal voluntary peak force associated with a greater variability of the relative contribution of each leg on the CoPres, enhanced all postural parameters of the non-exercised leg. A significant decreased of the tibialis anterior EMG activity for the Ex leg and an increased one for the NoEx leg. Finally, following unilateral fatigue, the body sway destabilisation seemed to occur only along the medio-lateral (ML) axis.The enhanced and greater variability of the variance along ML axis might be explained by the recourse at the loading–unloading strategy choice and suggests a central attempt to compensate for pain sensation.     

Aging effects on posture-related modulation of stretch reflex excitability in the ankle muscles in humans

The purpose of this study was to examine the effects of aging on posture-related changes of the stretch reflex excitability in the ankle extensor, soleus (SOL), and flexor, tibialis anterior (TA) muscles. Fourteen neurologically normal elderly (mean 68 ± 6 years) and 12 young (mean 27 ± 3 years) subjects participated. Under two postural conditions, upright standing (STD) and sitting (SIT), stretch reflex electromyographic (EMG) responses in the SOL/TA muscle were elicited by imposing rapid ankle dorsi-/plantar-flexion. Under the SIT condition, subjects were asked to keep the SOL background EMG level, which is identical to that under the STD condition. In the SOL muscle, both groups showed significant enhancement of the short-latency stretch reflex (SLR) response when the posture changed from SIT to STD. In the TA muscle, the young group showed significant enhancement of the middle- (MLR) and long-latency stretch reflex (LLR) when the posture changed from SIT to STD; no such modulation was observed in the elderly group. Since the TA stretch reflex responses under the STD condition were comparable in the young and elderly groups, the lack of posture-related modulation of the TA muscle in the elderly group might be explained by augmented stretch reflex excitability under the SIT condition. The present results suggest that the (1) SOL SLR responses are modulated both in the young and elderly subjects when the posture is changed from SIT to STD, (2) TA MLR and LLR responses are not modulated in the elderly subjects when the posture is changed from SIT to STD, while each response is same between the young and elderly in STD, and (3) the effect of aging on the posture-related stretch reflex differs in the SOL and TA muscles.     

A model-based study of passive joint properties on muscle effort during static stance

This study examined the impact of lower extremity joint stiffnesses and simulated joint contractures on the muscle effort required to maintain static standing postures after a spinal cord injury (SCI). Static inverse computer simulations were performed with a three-dimensional 15 degree of freedom musculoskeletal model placed in 1600 different standing postures. The required lower extremity muscle forces were calculated through an optimization routine that minimized the sum of the muscle stresses squared, which was used as an index of the muscle effort required for each standing posture. Joint stiffnesses were increased and decreased by 100 percent of their nominal values, and contractures were simulated to determine their effects on the muscle effort for each posture. Nominal muscle and passive properties for an individual with a SCI determined the baseline muscle effort for comparisons. Stiffness changes for the ankle plantar flexion/dorsiflexion, hip flexion/extension, and hip abduction/adduction directions had the largest effect on reducing muscle effort by more than 5 percent, while changes in ankle inversion/eversion and knee flexion/extension had the least effect. For erect standing, muscle effort was reduced by more than 5 percent when stiffness was decreased at the ankle plantar flexion/dorsiflexion joint or hip flexion/extension joint. With simulated joint contractures, the postural workspace area decreased and muscle effort was not reduced by more than 5 percent for any posture. Using this knowledge, methods can be developed through the use of orthoses, physical therapy, surgery or other means to appropriately augment or diminish these passive moments during standing with a neuroprosthesis.     

Alterations in evertor/invertor muscle activation and center of pressure trajectory in participants with functional ankle instability

Participants with ankle instability demonstrate more foot inversion during the stance phase of gait than able-bodied subjects. Invertor excitation, coupled with evertor inhibition may contribute to this potentially injurious position. The purpose of this experiment was to examine evertor/invertor muscle activation and foot COP trajectory during walking in participants with functional ankle instability (FI). Twelve subjects were identified with FI and matched to healthy controls. Tibialis anterior (TA) and peroneus longus (PL) electromyography (EMG), as well as COP, were recorded during walking. Functional analyses were used to detect differences between FI and control subjects with respect to normalized EMG and COP trajectory during walking. Relative to matched controls, COP trajectory was more laterally deviated in the FI group from 20% to 90% of the stance phase. TA activation was greater in the FI group from 15% to 30% and 45% to 70% of stance. PL activation was greater in the FI group at initial heel contact and toe off and trended lower from 20% to 40% of stance in the FI group. Altered motor strategies appear to contribute to COP deviations in FI participants and may increase the susceptibility to repeated ankle inversion injury.     

Synergistic co-activation in multi-directional postural control in humans

To examine the muscle synergies of multi-directional postural control, we calculated the target-directed variance fraction (η) and net action direction of each muscle using the electromyogram-weighted averaging (EWA) method. Subjects stood barefoot on a force platform and maintained their posture by producing a center of pressure (COP) in twelve target directions. Surface electromyograms were recorded from 6 right-sided muscles: tibialis anterior (TA), soleus (SOL), lateral gastrocnemius (LG), medial gastrocnemius (MG), fibularis longus (FL), and gluteus medius (GM). η was calculated from COP with duration of 20-s, during which the COP was relatively constant. The EWA method was applied to the EMG and the two COP components to estimate the net action direction of each muscle. The results showed that η values in all directions did not cross the 0.8 threshold. This suggests that human postural control is achieved by synergistic co-activation. The EWA revealed that the net action directions of TA, SOL, LG, MG, and GM were 277.6°, 71.1°, 87.7°, 94.0°, and 2.2°, respectively. This suggests that postural maintenance by muscle synergy can be attributed to the relevant muscles having various action directions. These results demonstrate that muscle synergies can be investigated using COP fluctuations.     

Effects of postural muscle fatigue on the relation between segmental posture and movement.

The purpose of this study was to examine whether fatigue of postural muscles might influence the coordination between segmental posture and movement. Seven healthy adults performed series of fifteen fast wrist flexions and extensions while being instructed to keep a dominant upper limb posture as constant as possible. These series of voluntary movements were performed before and after a fatiguing submaximal isometric elbow flexion, and also with or without the help of an elbow support. Surface EMG from muscles Delto?deus anterior, Biceps brachii, Triceps brachii, Flexor carpi ulnaris, Extensor carpi radialis were recorded simultaneously with wrist, elbow and shoulder accelerations and wrist and elbow displacements. Fatigue was evidenced by a shift of the elbow and shoulder muscles EMG spectra towards low frequencies. Kinematics of wrist movements and corresponding activations of wrist prime-movers, as well as the background of postural muscle activation before wrist movement were not modified. There were only slight changes in timing of postural muscle activations. These data indicate that postural fatigue induced by a low-level isometric contraction has no effect on voluntary movement and requires no dramatic adaptation in postural control.     

The effect of postural correction on muscle activation amplitudes recorded from the cervicobrachial region

In clinical practice, postural correction is a common treatment approach for individuals with neck and shoulder pain. As chronic static muscle use is thought to be associated with the onset of some neck and shoulder pain syndromes, it is important to understand the impact a postural correction program might have on muscle activation amplitudes in the neck and shoulder regions. Normalized surface electromyographic data were recorded from the levator scapulae, upper trapezius, supraspinatus, posterior deltoid, masseter, rhomboid major, cervical erector spinae, and sternocleidomastoid muscles of the dominant side of each of eighteen healthy subjects. Subjects performed five repetitions of each of four seated typing postures (habitual, corrected, head-forward and slouched) and four standing postures (habitual, corrected, and head-forward and slouched). Repeated-measures analysis of variance models (α = 0.05) revealed that in sitting postural correction tended to decreased the level of muscle activation required in all muscles studied during seated computer work, however this finding was not statistically significant. Corrected posture in sitting did, however produce a statistically significant reduction in muscle activity compared to forward head posture. Corrected posture in standing required more muscle activity than habitual or forward head posture in the majority of cervicobrachial and jaw muscles, suggesting that a graduated approach to postural correction exercises might be required in order to train the muscles to appropriately withstand the requirements of the task. A surprising finding was that muscle activity levels and postural changes had the largest impact on the masseter muscle, which demonstrated activation levels in the order of 20% maximum voluntary electrical activation.     

Effect of long-duration spaceflight on postural control during self-generated perturbations.

This report is the first systematic evaluation of the effects of prolonged weightlessness on the bipedal postural control processes during self-generated perturbations produced by voluntary upper limb movements. Spaceflight impacts humans in a variety of ways, one of which is compromised postflight postural control. We examined the neuromuscular activation characteristics and center of pressure (COP) motion associated with arm movement of eight subjects who experienced long-duration spaceflight (3--6 mo) aboard the Mir space station. Surface electromyography, arm acceleration, and COP motion were collected while astronauts performed rapid unilateral shoulder flexions before and after spaceflight. Subjects generally displayed compromised postural control after flight, as evidenced by modified COP peak-to-peak anterior-posterior and mediolateral excursion, and pathlength relative to preflight values. These changes were associated with disrupted neuromuscular activation characteristics, particularly after the completion of arm acceleration (i.e., when subjects were attempting to maintain upright posture in response to self-generated perturbations). These findings suggest that, although the subjects were able to assemble coordination modes that enabled them to generate rapid arm movements, the subtle control necessary to maintain bipedal equilibrium evident in their preflight performance is compromised after long-duration spaceflight.     

The effect of textured surfaces on postural stability and lower limb muscle activity

Textured insoles may enhance sensory input on the plantar surfaces of the feet, thereby influencing neuromuscular function. The aim of this study was to investigate whether textured surfaces alter postural stability and lower limb muscle activity during quiet bipedal standing balance with eyes open. Anterior–posterior (AP) and mediolateral (ML) sway variables and the intensity of electromyographic (EMG) activity in eight dominant lower limb muscles were collected synchronously over 30 s in 24 young adults under three randomised conditions: control surface (C), texture 1 (T1) and texture 2 (T2). Repeated measures ANOVA showed that the textured surfaces did not significantly affect AP or ML postural sway in comparison to the control condition (p > 0.05). Neither did the textured surfaces significantly alter EMG activity in the lower limbs (p > 0.05). Under the specific conditions of this study, texture did not affect either postural sway or lower limb muscle activity in static bipedal standing. The results of this study point to three areas of further work including the effect of textured surfaces on postural stability and lower limb muscle activity: (i) in young healthy adults under more vigorous dynamic balance tests, (ii) post-fatigue, and (iii) in older adults presenting age-related deterioration.     

Time course and variability of tendinous vibration-induced postural reactions in forward and backward directions

Mechanical vibration of tendons induces large postural reactions (PR-VIB) but little is known about how these reactions vary within and between subjects. We investigated the intra- and inter-individual variability of PR-VIB and determined the reliability of center of pressure (COP) measures. Bipodal postural control (eyes closed) of 30 healthy adults were evaluated using a force platform under 02 conditions: bilateral VIB of the tibialis anterior (TA) and Achilles tendons (ACH-T) at 80 Hz. Each condition consisted of 03 trials of 30 s duration (Baseline: 10 s; VIB: 10 s; POST-VIB: 10 s). The Amplitude and Velocity of the COP in the antero-posterior/medio-lateral (AP/ML) directions were recorded and analyzed according to 5 time-windows incremented every 2 s of vibration (i.e. the first 2 s; 4 s; 6 s; 8 s & 10 s), whereas the COP position/AP was monitored every 0.5 s. All postural parameters increased significantly during TA and ACH-T vibration compared to the Baseline. The reliability of the COP measures showed good ICC scores (0.40-0.84) and measurement errors that varied depending on the duration of VIB time-windows. The COP position/AP reveals a lower intra- and inter-subject variability of PR-VIB in the first 2 s of VIB. The metrological characteristics of PR-VIB should be investigated further to guide their future use by clinicians and researchers.     

Posture effects on timing of abdominal muscle activity during stimulated ventilation.

In humans during stimulated ventilation, substantial abdominal muscle activity extends into the following inspiration as postexpiratory expiratory activity (PEEA) and commences again during late inspiration as preexpiratory expiratory activity (PREA). We hypothesized that the timing of PEEA and PREA would be changed systematically by posture. Fine-wire electrodes were inserted into the rectus abdominis, external oblique, internal oblique, and transversus abdominis in nine awake subjects. Airflow, end-tidal CO2, and moving average electromyogram (EMG) signals were recorded during resting and CO2-stimulated ventilation in both supine and standing postures. Phasic expiratory EMG activity (tidal EMG) of the four abdominal muscles at any level of CO2 stimulation was greater while standing. Abdominal muscle activities during inspiration, PEEA, and PREA, were observed with CO2 stimulation, both supine and standing. Change in posture had a significant effect on intrabreath timing of expiratory muscle activation at any level of CO2 stimulation. The transversus abdominis showed a significant increase in PEEA and a significant decrease in PREA while subjects were standing; similar changes were seen in the internal oblique. We conclude that changes in posture are associated with significant changes in phasic expiratory activity of the four abdominal muscles, with systematic changes in the timing of abdominal muscle activity during early and late inspiration.     

Pelvic Morphology,Body Posture and Standing Balance Characteristics of Adolescent Able-Bodied and Idiopathic Scoliosis Girls

The purpose of this study was to determine how pelvic morphology, body posture, and standing balance variables of scoliotic girls differ from those of able-bodied girls, and to classify neuro-biomechanical variables in terms of a lower number of unobserved variables. Twenty-eight scoliotic and twenty-five non-scoliotic able-bodied girls participated in this study. 3D coordinates of ten anatomic body landmarks were used to describe pelvic morphology and trunk posture using a Flock of Birds system. Standing balance was measured using a force plate to identify the center of pressure (COP), and its anteroposterior (AP) and mediolateral (ML) displacements. A multivariate analysis of variance (MANOVA) was performed to determine differences between the two groups. A factor analysis was used to identify factors that best describe both groups. Statistical differences were identified between the groups for each of the parameter types. While spatial orientation of the pelvis was similar in both groups, five of the eight trunk postural variables of the scoliotic group were significantly different that the able-bodied group. Also, five out of the seven standing balance variables were higher in the scoliotic girls. Approximately 60% of the variation is supported by 4 factors that can be associated with a set of variables; standing balance variables (factor 1), body posture variables (factor 2), and pelvic morphology variables (factors 3 and 4). Pelvic distortion, body posture asymmetry, and standing imbalance are more pronounced in scoliotic girls, when compared to able-bodied girls. These findings may be beneficial when addressing balance and ankle proprioception exercises for the scoliotic population.