Increased knee flexion and varus moments during gait with high-heeled shoes: A systematic review and meta-analysis

BackgroundHigh-heeled shoes have been thought to alter lower extremity joint mechanics during gait, however its effects on the knee remain unclear.Research questionThis systematic review and meta-analysis aimed to determine the effects of high-heeled shoes on the sagittal- and frontal-plane knee kinetics/kinematics during gait.Methods1449 studies from 6 databases were screened for the following criteria: 1) healthy adult females, 2) knee joint kinematics/kinetics reported for the early stance phase during gait under varying shoe heel heights (including barefoot). Excluded studies included those mixing different shoe styles in addition to altering the heel heights. A total of 14 studies (203 subjects) met the selection criteria, resulting in 51 and 21 Cohen’s d effect sizes (ESs) comparing the differences in knee sagittal- (flexion) and frontal-plane (varus) moment/angle, respectively, between shoes with higher heels and shoes with lower heels/barefoot.ResultsMeta-analyses yielded a significant medium-to-large effect of higher heels compared to lower heels on increasing knee flexion moment (overall ES = 0.83; P < 0.01), flexion angle (overall ES=0.46; P < 0.01), and varus moment (overall ES=0.52; P < 0.01) during the early stance phase of gait. The results of meta-regressions used to explore factors explaining the heterogeneity among study ESs revealed that a greater ES in the knee flexion moment was associated with an elevated heel height of the high-heeled shoes (P = 0.02) and greater body mass of the individuals (P = 0.012). A greater ES in the knee varus moment during high-heeled gait was associated with a greater body height (P = 0.003) and mass (P = 0.006).SignificanceGiven the association between increased knee flexion/varus moments and risk of developing knee osteoarthritis (OA), women who wear high-heel shoes frequently and for a long period may be more susceptible to knee OA. Preventive treatments, such as lower extremity muscle strengthening, may help improve shock absorption to decrease knee loading in high-heel users.     

The impact of shod vs unshod walking on center of pressure variability

BackgroundThe variability of center of pressure (COP) is a measure of stability commonly examined during quiet standing. While more recent research has examined the variability of COP during walking, an adequate comparison between shod and unshod walking conditions has yet to be made.Research questionWhat is the influence of athletic footwear on the variability of COP displacement during walking?MethodsIn this intervention study, twenty healthy women (age 18–30 years) completed 2, 10-min walking trials, 1 shod and 1 unshod, during which ground reaction forces (GRF) and COP movement were collected by an instrumental treadmill. COP displacement was examined in the medial-lateral (ML) and anterior-posterior (AP) directions after being divided into quadrants based on the peaks and trough of each steps associated vertical GRF. A single MANOVA was used to determine effects of footwear and limb for each quadrant with the probability of a Type I error set at 0.05.ResultsSignificant differences in variability were seen between footwear conditions in all quadrants in the AP direction and quadrants one and four in the ML direction. These results may be due to the structure of footwear, including midsole cushioning, altering the dynamics of the foot during walking.SignificanceThe results of this study suggest that on average, athletic footwear reduces the variability of COP displacement in ML and AP directions. This may have implications for populations for whom variability of COP is determined to be undesirable.     

Control of the motion of the body's center of mass in relation to the center of pressure during high-heeled gait

High-heeled shoes are associated with instability and falling, leading to injuries such as fracture and ankle sprain. Knowledge of the motion of the body's center of mass (COM) with respect to the center of pressure (COP) during high-heeled gait may offer insights into the balance control strategies and provide a basis for approaches that minimize the risk of falling and associated adverse effects. The study aimed to investigate the influence of the base and height of the heels on the COM motion in terms of COM–COP inclination angles (IA) and the rate of change of IA (RCIA). Fifteen females who regularly wear high heels walked barefoot and with narrow-heeled shoes with three heel heights (3.9 cm, 6.3 cm and 7.3 cm) while kinematic and ground reaction force data were measured and used to calculate the COM and COP, as well as the temporal-distance parameters. The reduced base of the heels was found to be the primary factor for the reduced normalized walking speed and the reduced frontal IA throughout the gait cycle. This was achieved mainly through the control of the RCIA during double-leg stance (DLS). The heel heights affected mainly the peak RCIA during DLS, which were not big enough to affect the IA. These results suggest young adults adopt a conservative strategy for balance control during narrow-heeled gait. The results will serve as baseline data for future evaluation of patients and/or older adults during narrow-heeled gait with the aim of reducing the risk of falling.     

Influence of high-heeled shoe parameters on biomechanical performance of young female adults during stair ascent motion

BackgroundHigh-heeled shoes are currently preferred by women due to contemporary aesthetics. However, high-heeled shoes may increase the effort required to ascend stairs and, hence, alter biomechanical performance.Research question: How do high-heel shoe parameters affect the pelvis position, lower extremities kinematics, and ground reaction force in young women during stair ascent motion?MethodsStair ascent experiments were performed with 20 healthy adult women. The participants were instructed to ascend a 3-step staircase, wearing heeled shoes of different heel heights and heel types and one pair of flat shoes as the control group. Changes in lower body biomechanics were analyzed with kinematics and ground reaction force variables collected from the dominant limb. A two-way repeated ANOVA was performed to determine which variables were affected by heel type and which were affected by heel height or a combination of both.ResultsAs the heel height increased, an increased range of ankle dorsiflexion-plantarflexion, as well as pelvic rotation, was observed(P = 0.039 and P = 0.003, respectively). A thinner heel type displayed a larger pelvic forward tilt movement(P = 0.026)and 1st peak vertical force(P = 0.025), as well as a smaller 2nd peak vertical force (P = 0.002). With high heels, increased external rotation of the knee, inversion and plantar flexion, and flexion values of the knee were observed. We also observed decreased external rotation of the pelvis, ankle eversion, varum, and dorsiflexion.SignificanceTo stabilize body posture during stair ascent motion with high-heeled shoes, compensatory response including increasd pelvic range of motion and changing the joint angles of the lower extremities.     

Reliability of center of pressure measures within and between sessions in individuals post-stroke and healthy controls

BackgroundKnowing the reliability of the center of pressure (COP) is important for interpreting balance deficits post-stroke, especially when the balance deficits can necessitate the use of short duration trials. The novel aspect of this reliability study was to examine the center of pressure measures using two adjacent force platforms between and within sessions in stroke and controls. After stroke, it is important to understand the contribution of the paretic and non-paretic leg to the motor control of standing balance. Because there is a considerable body of knowledge on COP reliability on a single platform, we chose to examine reliability using two adjacent platforms which has not been examined previously in stroke.MethodsTwenty participants post-stroke and 22 controls performed an arm raise, load drop and quiet stance balance task while standing on two adjacent force platforms, on two separate days. Intraclass correlations coefficient (ICC_2,1) and percentage standard error of measurement (SEM%) were calculated for COP velocity, ellipse area, anterior–posterior (AP) displacement, and medial–lateral (ML) displacement.ResultsBetween sessions, COP velocity was the most reliable with high ICCs and low SEM% across groups and tasks and ellipse area was less reliable with low ICCs across groups and tasks. COP measures were less reliable during the arm raise than load drop post-stroke. Within session reliability was high for COP velocity and ML displacement requiring no more than six trials across tasks.ConclusionsThe COP velocity was the most reliable measure with high ICCs between sessions and the high reliability was achieved with fewer trials in both groups in a single session.     

Postural control in adolescent boys and girls before the age of peak height velocity: Effects of task difficulty

BackgroundAdolescent children experience a critical developmental period marked by rapid biological changes.Research questionTo describe the longitudinal changes in postural control that occur in adolescent boys and girls before the age of peak height velocity (PHV).MethodsHere, to address the gap of knowledge, we compared the postural control and activation strategies of the muscles that control the ankle joint in twenty-three boys (age 12.5 ± 0.29) and twenty-one girls (age 10.5 ± 0.32). They performed easy (two legs) and difficult (two legs-eyes closed; one leg) postural balance tasks at 18 and 9 months before PHV and at PHV. We quantified the center of pressure (COP) displacements in the anterior-posterior (AP) and mediolateral (ML) directions and electromyographic (EMG) activity of tibialis anterior (TA) and medial gastrocnemius (MG) muscles.ResultsBoys exhibited greater AP and ML COP displacement than girls only for the one leg task (difficult task). Although boys and girls had similar postural control 18 months prior to PHV, girls exhibited lesser COP displacement at 9 months before PHV, which related to greater TA-MG coactivation (R² = 0.26; p < 0.01). In contrast, postural control was not different between boys and girls with an easy balance task (two legs) performed with eyes open and closed. Rather, we found that all children improved their COP displacement in the ML direction with maturity and both AP and ML COP was significantly lower with eyes open.ConclusionThese findings provide novel evidence that postural control is superior in early adolescent girls than boys 9 months prior to PHV, likely associated with an earlier maturation of muscle coordination.     

Dynamic balance is impaired after a match in young elite soccer players

PurposeThe aim of this study is to assess the effect of actual match effort on dynamic balance abilities in young elite soccer players.MethodsSeventeen Under 15 male players who compete at national level participated in the study. Their dynamic balance was assessed by having them jump starting with both feet on the ground in a standing position and land on one foot only. Their vertical time to stabilization (vTTS) and postural sway were calculated before and after 35 min of an unofficial match. Postural sway was assessed on the basis of center-of-pressure (COP) trajectories. Parameters considered were sway area, COP displacements in the antero-posterior (AP) and medio-lateral (ML) directions and COP path length.ResultsAfter the match, a significant increase in vTTS (p = 0.007) COP path length (p = 0.001) and COP displacements in ML (p < 0.001) was observed. Such effects involve both non-dominant (vTTS, path length) and dominant limb (COP displacements).ConclusionsThe physical effort associated with the match induces significant impairments of players' dynamic balance abilities. On the basis of such findings, coaches might consider integrating training sessions with specific balance exercises as well as performing injury-prevention routines even when players are fatigued, to better adapt them to match conditions.     

A multiple domain postural control assessment in people with Parkinson’s disease: traditional,non-linear,and rambling and trembling trajectories analysis

BackgroundPostural impairment is one of the most debilitating symptoms in people with Parkinson's disease (PD), which show faster and more variable oscillation during quiet stance than neurologically healthy individuals. Despite the center of pressure parameters can characterize PD’s body sway, they are limited to uncover underlying mechanisms of postural stability and instability.Research questionDo a multiple domain analysis, including postural adaptability and rambling and trembling components, explain underlying postural stability and instability mechanisms in people with PD?MethodTwenty-four individuals (12 people with PD and 12 neurologically healthy peers) performed three 60-s trials of upright quiet standing on a force platform. Traditional and non-linear parameters (Detrended Fluctuation Analysis- DFA and Multiscale Entropy- MSE) and rambling and trembling trajectories were calculated for anterior-posterior (AP) and medial-lateral (ML) directions.ResultsPDG’s postural control was worse compared to CG, displaying longer displacement, higher velocity, and RMS. Univariate analyses revealed largely longer displacement and RMS only for the AP direction and largely higher velocity for both AP and ML directions. Also, PD individuals showed lower AP complexity, higher AP and ML DFA, and increased AP and ML displacement, velocity, and RMS of rambling and trembling components compared to neurologically healthy individuals.SignificanceBased upon these results, people with PD have a lower capacity to adapt posture and impaired both rambling and trembling components compared to neurologically healthy individuals. These findings provide new insights to explain the larger, faster, and more variable sway in people with PD.     

Evaluation of sitting and standing postural balance in cerebral palsy by center-of-pressure measurement using force plates: comparison with clinical measurements

BackgroundCenter-of-pressure (CoP) measurements have been studied for assessing balance control. While CoP measurements using force plates have been used to assess standing balance in children with cerebral palsy (CP), it has not been assessed in a sitting position, which specifically reflects trunk postural control.Research questionThe purpose of this study was to compare CoP measurements using force plates during both standing and sitting trials with the Pediatric Balance Scale (PBS) in children with spastic CP.MethodsWe recruited 26 children with spastic CP (7.8 ± 3.4 years, 4–13 years) and used the PBS, a validated evaluation tool that measures static and dynamic balance control. We took CoP measurements using force plates during sitting and standing. For both trials, subjects stayed still for 10 s with their eyes open or closed. We calculated the CoP velocity, mediolateral (ML) and anteroposterior (AP) velocity, and ML and AP displacements of CoP.Results and SignificanceDuring standing trials, static PBS standing scores negatively correlated with more AP displacement and velocity than ML displacement and velocity (p < 0.05). During sitting trials, dynamic PBS sitting scores negatively correlated with ML displacement and velocity (p < 0.05). CoP parameters in the ML direction of the sitting position and CoP parameters in the AP direction of the standing position may better reflect the balance control in children with spastic CP.     

Rambling-trembling center-of-pressure decomposition reveals distinct sway responses to simulated somatosensory deficit

BackgroundFalls in older adults are often multifactorial, but can be linked to diminished sensation capabilities from age-related neural degeneration. Rambling-trembling (RM-TR) decomposition may provide insight into the relation between sensorineural function and postural sway, with both research and clinical applications.Research questionWhat are the effects of perturbed somatosensation on RM-TR-derived measures of center of pressure (COP) during quiet standing?MethodsFifty-two healthy young adults (22.10 ± 1.88 years) participated in the study. Participants stood on two force plates with a standardized stance width and foot angle, with eyes open (EO) or eyes closed (EC). Foam with different thicknesses ranging from 1/8″ to 1″ (F1-F4) was placed under the feet to interfere with intact sensory input and simulate varying degrees of somatosensory deficit. Force and moment data were used to calculate COP, RM, and TR time series. Mean velocity, acceleration, and jerk in the anteroposterior (AP) and mediolateral direction (ML) were extracted for comparison.ResultsThe EO condition remained relatively constant regardless of foam thickness. The EC condition showed increasing changes from baseline to each of the foam conditions. COP captures the smallest change in foam thickness, but RM provides a robustness across parameters that is not found in COP or TR. RM jerk in the AP direction showed significantly greater changes from baseline to F4 than the COP or TR counterparts. In the ML direction, TR jerk showed a sharper contrast between foam conditions than COP and RM.SignificanceFindings suggest that RM-TR-derived measures may act as a compliment to, or provide a greater degree of sensitivity than, traditional COP measures and aid in the initial detection and monitoring of fall risk in aging and pathological populations.     

Deficits in time-to-boundary measures of postural control with chronic ankle instability

Our purpose was to examine postural control in single leg stance in subjects with and without unilateral chronic ankle instability (CAI) using traditional center of pressure (COP)-based and time-to-boundary (TTB) measures. Fifteen physically active females with self-reported unilateral chronic ankle instability (CAI) and nine healthy female controls performed three 10-s trials of eyes open single limb quiet standing on a force plate on both their legs. The traditional measures were mean COP velocity, standard deviation of COP, range of COP, and percent of available range utilized. The TTB measures were absolute minimum TTB, mean of the minimum TTB samples, and standard deviation of the minimum TTB samples. All measures were calculated in both the mediolateral (ML) and anteroposterior (AP) directions. A 2x2 group (CAI, control) by side (involved, uninvolved) design was utilized. The CAI group had significantly lower scores for five of the six TTB measures compared to the control group, however only one (AP COP velocity) of the eight traditional measures was different between groups. The TTB measures appear to detect postural control deficits related to CAI that traditional measures do not.     

Effects of assistive devices on postural control following a balance disturbance along the anterior-posterior direction

BackgroundAssistive devices provide balance and stability to those who require a greater base of support, especially during ambulation or in tasks essential to functional daily living. In ambulatory assistive device use, center of pressure (COP) movement as one of the measurements of postural control is a factor when assessing fall risk, with an overall goal of maintaining postural equilibrium. There is a lack of research on assistive devices, such as walkers, regarding measurable outcome variables related to fall risk. The purpose of this study was to determine how much the postural control in single limb stance during a balance perturbance is affected by utilizing three different walker types designed to promote stability: the standard walker, the front-wheeled walker with straight wheels and the front-wheeled walker with caster wheels.Research questionIs postural sway control in single limb stance during a balance perturbance affected by walker type?MethodsTwenty-three healthy adults participated and gave consent. The NeuroCom® SMART EquiTest® system was utilized to simulate forward falls. Subjects stood on the system’s force plate, which was tipped backwards quickly, forcing subjects to attempt to maintain balance. Each participant experienced 18 simulated perturbations, during which they were asked to maintain balance while using one of three walkers in single-limb stance. Each trial was completed using random assignment of three different walker types. Leg dominance of the stance leg was also randomized for each trial.ResultsThe type of walker and the leg dominance in the standing limb significantly affected postural control in a balance perturbance in the A-P direction. The walker type significantly affected the COP maximum displacement in anterior-posterior (AP) direction. However, the leg dominance significantly affected COP maximum displacement in AP and medio-lateral (ML) directions and COP velocity in AP direction.SignificanceThe findings suggest that when fully grounded, a standard walker is more stable than the front-wheeled walker. However, this does not indicate that the standard walker is more stable than other types of walkers when it is being picked up and moved forward during normal use.     

Characterizing inter-limb synchronization after incomplete spinal cord injury: A cross-sectional study

BackgroundIndividuals with incomplete spinal cord injury (iSCI) demonstrate greater postural sway and increased dependency on vision to maintain balance compared to able-bodied individuals. Research on standing balance after iSCI has focused on the joint contribution of the lower limbs; however, inter-limb synchrony in quiet standing is a sensitive measure of individual limb contributions to standing balance control in other neurological populations. It is unknown if and how reduced inter-limb synchrony contributes to the poor standing balance of individuals with iSCI.Research questionHow does an iSCI affect inter-limb synchrony and weight-bearing symmetry in standing?MethodsEighteen individuals with non-progressive motor iSCI and 15 age- and sex-matched able-bodied individuals (M-AB) were included in the study. Participants stood in a standardized position on two adjacent force plates in eyes open and closed conditions for 70 s per condition. Net centre-of-pressure (COP) root mean square (RMS), net COP velocity, COP inter-limb synchrony (i.e. cross-correlation between left and right COP), and weight-bearing asymmetry (i.e. vertical force from each limb over total vertical force) were calculated. Muscle strength of the lower limbs was assessed with manual muscle testing.ResultsIndividuals with iSCI demonstrated reduced inter-limb synchrony when standing with eyes open and eyes closed, but did not differ to M-AB with respect to weight-bearing asymmetry. They also produced greater net COP RMS and velocity when compared to M-AB. Muscle strength of the two lower limbs demonstrated an overall asymmetry in individuals with iSCI.SignificanceIndividuals with iSCI demonstrated impaired balance control as evidenced by reduced inter-limb synchrony and greater COP RMS and velocity compared to M-AB individuals. This increased understanding of how balance control is impaired following iSCI may inform balance assessment and intervention for this population. Future work examining the association between inter-limb synchrony and the occurrence of falls in iSCI is warranted.     

Quantification of the path of center of pressure (COP) using an F-scan in-shoe transducer

By tracking the path of the center of pressure (COP) during the stance phase, the balance and pattern of progression can be determined. The path of COP is frequently used in clinical practice, although it is not quantified. In this study, an F-scan pressure sensitive insole system was used to quantify the path of COP. The COP of initial contact and the average during the stance phase corresponded to the center of the heel and to the center of the total plantar surface, respectively. The COP displacement corresponded to 83% of foot contact length and 18% of forefoot contact width. When the longitudinal axis of the insole was plotted as the Y-axis and the transverse axis of the insole as X-axis, the slopes of the COP coordinates during stance phase was 6° inward. Velocities of the COP during each functional rocker action were even and 22–27 cm/s. The changes of quantified COP parameters according to the biomechanical alteration of the foot were confirmed by high-heeled gait.     

Multiscale entropy identifies differences in complexity in postural control in women with multiple sclerosis

Loss of postural center-of-pressure complexity (COP complexity) has been associated with reduced adaptability that accompanies disease and aging. The aim of this study was to identify if COP complexity is reduced: (1) in those with Multiple Sclerosis (MS) compared to controls; (2) when vision is limited compared to remaining intact; and (3) during more demanding postural conditions compared to quiet standing. Additionally, we explored the relationship between the COP complexity and disease severity, fatigue, cutaneous sensation and central motor drive. Twelve women with MS and 12 age-matched controls were tested under quiet standing and postural maximal lean conditions with normal and limited vision. The key dependent variable was the complexity index (C_I) of the center of pressure. We observed a lower C_I in the MS group compared to controls in both anterior-posterior (AP) and medio-lateral (ML) directions (p's < 0.002), during the performance of maximal self-regulated leans (AP: p < 0.001; ML: p = 0.018), and under limited vision (AP: p = 0.001; ML: p = 0.006). No group-by-vision interaction (p > 0.05) was observed, indicating that limiting vision did not impact COP complexity differently in the two groups. Decreased cutaneous sensitivity was associated with lower C_I values in the AP direction among those with MS (r² = 0.57); all other measures did not exhibit significant relationships. The findings reported here suggest that (1) MS is associated with diminished COP complexity under both normal and challenging postures, and (2) complexity is strongly correlated with cutaneous sensitivity, suggesting the unique contribution of impaired somatosensation on postural control deficits in persons with MS.     

Augmented feedback of COM and COP modulates the regulation of quiet human standing relative to the stability boundary

The experiment manipulated real-time kinematic feedback of the motion of the whole body center of mass (COM) and center of pressure (COP) in anterior-posterior (AP) and medial-lateral (ML) directions to investigate the variables actively controlled in quiet standing of young adults. The feedback reflected the current 2D postural positions within the 2D functional stability boundary that was scaled to 75%, 30% and 12% of its original size. The findings showed that the distance of both COP and COM to the respective stability boundary was greater during the feedback trials compared to a no feedback condition. However, the temporal safety margin of the COP, that is, the virtual time-to-contact (VTC), was higher without feedback. The coupling relation of COP–COM showed stable in-phase synchronization over all of the feedback conditions for frequencies below 1 Hz. For higher frequencies (up to 5 Hz), there was progressive reduction of COP–COM synchronization and local adaptation under the presence of augmented feedback. The findings show that the augmented feedback of COM and COP motion differentially and adaptively influences spatial and temporal properties of postural motion relative to the stability boundary while preserving the organization of the COM–COP coupling in postural control.     

The influence of heel height on patellofemoral joint kinetics during walking

Although wearing high-heeled shoes has long been considered a risk factor for the development for patellofemoral pain (PFP) in women, patellofemoral joint kinetics during high-heeled gait has not been examined. The purpose of this study was to determine if heel height increases patellofemoral joint loading during walking. Eleven healthy women (mean age 25.0±3.1 yrs) participated. Lower extremity kinematics and kinetics were obtained under 3 different shoe conditions: low heel (1.27 cm), medium heel (6.35 cm), and high heel (9.53 cm). Patellofemoral joint stress was estimated using a previously described biomechanical model. Model outputs included patellofemoral joint reaction force, patellofemoral joint stress and utilized contact area as a function of the gait cycle. One-way ANOVAs with repeated measures were used to compare the model outputs and knee joint angles among the 3 shoe conditions. Peak patellofemoral joint stress was found to increase significantly (p=0.002) with increasing heel height (low heel: 1.9±0.7 MPa, medium heel: 2.6±1.2 MPa, and high heel: 3.6±1.5 MPa). The increased patellofemoral joint stress was mainly driven by an increase in joint reaction force owing to higher knee extensor moments and knee flexion angles. Our findings support the premise that wearing high-heeled shoes may be a contributing factor with respect to the development of PFP.     

Generalizability of center of pressure measures of quiet standing

Center of pressure (COP) measures are commonly used as indicators of balance and postural control. At present, there are no universally accepted standards in research investigating fluctuations in the COP with regard to the number of trials or the length of a given trial. The purpose of this study was to use the tools of Generalizability Theory (G-Theory) to investigate the reliability of COP measures of quiet standing and to establish an optimal measurement protocol. G-Theory provides a tool that allows us to break down the sources of variation, or facets, in a measurement procedure and ultimately design a protocol that provides optimal reliability. Fifteen participants completed 10 90-s trials with eyes open and closed. COP measures of anterior-posterior standard deviation (SD(AP)), medial-lateral SD (SD(ML)), average velocity (Vel), and 95% confidence ellipse area (Area) were calculated using the first 30, 60, and 90s of each trial. A G-study and follow-up D-studies were performed to estimate reliability coefficients (G-coefficients). The results of the G-Theory analysis suggest that these COP measures reached acceptable levels of reliability (G>or=0.70) with at least five 60s trials.     

Aging, muscle activity, and balance control: physiologic changes associated with balance impairment

Older adults demonstrate increased amounts of postural sway, which may ultimately lead to falls. The mechanisms contributing to age-related increases in postural sway and falls in the elderly remain unclear. In an effort to understand age-related changes in posture control, we assessed foot center-of-pressure (COP) displacements and electromyographic data from the tibialis anterior, soleus, vastus lateralis, and biceps femoris collected simultaneously during quiet-standing trials from elderly fallers, elderly non-fallers, and healthy young subjects. Both traditional measures of COP displacements and stabilogram-diffusion analysis were used to characterize the postural sway of each group. Regression analyses were used to assess the relationship between the COP measures and muscle activity. Elderly fallers demonstrated significantly greater amounts of sway in the anteroposterior (AP) direction and greater muscle activity during quiet standing compared with the young subjects, while elderly non-fallers demonstrated significantly greater muscle activation and co-activation compared with the young subjects. No significant differences were found between elderly fallers and elderly non-fallers in measures of postural sway or muscle activity. However, greater postural sway in both the AP and mediolateral (ML) directions and trends of greater muscle activity were found in those older adults who demonstrated lower scores on clinical measures of balance. In addition, short-term postural sway was found to be significantly correlated with muscle activity in each of these groups. This work suggests that high levels of muscle activity are a characteristic of age-related declines in postural stability and that such activity is correlated with short-term postural sway. It is unclear whether increases in muscle activity preclude greater postural instability or if increased muscle activity is a compensatory response to increases in postural sway.     

Analysis of muscular fatigue and foot stability during high-heeled gait.

Plantar pressure measurements and surface electromyography (EMG) were used to determine the effects of muscular fatigue induced by high-heeled gait. The medio-lateral (M/L) stability of the foot was characterized by measuring the M/L deviations of the center of pressure (COP) and correlating these data with fatigue of lower-limb muscles seen on EMG. EMG measurements from habitual high-heeled shoe wearers demonstrated an imbalance of gastrocnemius lateralis versus gastrocnemius medialis activity in fatigue conditions, which correlated with abnormal lateral shifts in the foot-ground or shoe-ground COP of these women.