Net Center Of Pressure Research Articles

Is a portable pressure plate an alternative to force plates for measuring postural stability and interlimb coordination of quiet standing balance control?

Center-of-pressure (COP) synchronization and symmetry can inform adaptations in balance control following one-sided sensorimotor impairments (e.g., stroke). As established force plates are impossible to transport, we aimed to criterion validate a portable pressure plate for obtaining reliable COP synchronization and symmetry measures, next to conventional postural stability measures. Twenty healthy adults participated. In a single session, three 40-s eyes-open and eyes-closed quiet stance trials were performed per plate-type, randomly ordered. Individual-limb COPs were measured to calculate between-limb synchronization (BLS) and dynamic control asymmetry (DCA). Net COP (i.e., limbs combined) area, amplitude, and velocity were used to describe anteroposterior (AP) and mediolateral (ML) postural stability. Criterion validity was evaluated using Spearman correlations (r) and Bland-Altman plots. Test-retest reliability was tested using intraclass correlation coefficients (ICC). Strong correlations (r > 0.75) and acceptable reliability (ICC > 0.80) were found regarding individual-limb COP velocity and DCA, net COP ML amplitude and AP and ML velocities. Bland-Altman plots yielded possible proportional bias; the pressure plate systematically underestimated COP scores by force plates and a larger error associated with a larger measurement. Despite correlations between instruments and sufficient reliability for measuring postural stability and DCA, this technical note strongly suggests, due to a systematic deviation, using the same plate-type to accurately assess performance change within subjects longitudinally over time.

Modern smartphone usage can negatively impact postural balance while standing on dynamically challenging grounds

BackgroundWhile several studies have explored the impacts of smartphone usage on postural balance, their tasks are limited to texting or calling, and the studies were performed on rigid ground. Research questions1.How does modern smartphone usage, specifically taking selfies or posting statuses on social media, affect balance?2.How does their interaction with challenging ground conditions affect balance? MethodsSixteen healthy young adults were recruited to perform two smartphone tasks: taking selfies and posting statuses on social media; participants were standing on four different grounds: rigid, foam-based compliant, robot-simulated compliant, and robot-simulated oscillatory grounds. The center-of-pressure (CoP) under each foot was recorded via force plates and the net CoP was calculated. Temporal, spatial, and control aspects of postural balance were analyzed by virtual time-to-contact (VTC), CoP path length (PL) and sway area (SA), and switching rate (SR), respectively. Two-way repeated measures analysis of variance (ANOVA) tests were performed for each dependent variable to compare the mean differences between smartphone tasks and ground conditions and their interaction effect. Paired t-tests with Bonferroni correction were used to determine significant differences in post-hoc analyses. ResultsVTC decreased significantly whereas CoP PL and SA increased significantly during smartphone usage (all p-values <0.001). Interaction effects between task and ground condition (all p-values <0.001) were observed in all measures but SR, implying that the effect of smartphone usage on postural balance can significantly change depending on the ground condition. SignificanceThese results highlight the potential fall risks due to the impact of modern smartphone usage on standing balance. Understanding the effect of smartphone usage on standing balance and the interaction effect with various ground conditions opens the door for potential balance assistive devices and mobile phone applications to minimize falls.

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.

Spectral analysis of centre of pressure identifies altered balance control in individuals with moderate-severe traumatic brain injury

Purpose: To identify impairments and recovery of balance control after moderate-severe traumatic brain injury (TBI) through spectral analyses of static balance tasks and to characterise the contributions of each limb to balance control.Methods: A retrospective analysis of longitudinal balance data from force platforms at 2, 5, and 12 months post-injury in 31 individuals with moderate to severe TBI was performed. Single-visit data from age-matched controls (n = 22) were collected for descriptive comparison. Net and individual limb centre of pressure measures and inter-limb centre of pressure coherence were calculated in low (≤0.4 Hz) and high (≥0.4 Hz) frequencies in the anteroposterior and mediolateral directions during standing with the eyes open and closed.Results: Standing with the eyes closed increased net centre of pressure spectral power in low and high frequencies. Individuals with TBI demonstrated recovery in high frequencies in net centre of pressure in the mediolateral direction. Inter-limb coherence in the anteroposterior and mediolateral directions increased (recovered) over time in high frequencies. Weight-bearing asymmetry was visible in high frequencies in the anteroposterior and mediolateral directions.Conclusions: Increased amplitude of low and high-frequency power suggests that individuals with TBI included in this study have impaired anticipatory and reactive balance mechanisms, which may be driven by weight-bearing asymmetries and which recover over time.Implications for rehabilitationAnticipatory and reactive balance impairments after traumatic brain injury may place individuals at increased risk for falls.Analyses from postural sway in static balance tasks infer changes in anticipatory or reactive balance control after traumatic brain injury.Addressing weight-bearing asymmetries in rehabilitation interventions post-traumatic brain injury may improve between-limb coordination for anticipatory and reactive balance control.

Characterization of Balance Control After Moderate to Severe Traumatic Brain Injury: A Longitudinal Recovery Study.

Balance impairments after traumatic brain injury (TBI) are common and persist after injury. Postural asymmetries in balance have been reported, but not quantified, across recovery. The objective of this study was to characterize balance recovery after moderate to severe TBI, with a focus on postural asymmetry. A secondary analysis of prospectively collected data was used in this study. Data were from 45 participants with moderate to severe TBI. Participants' balance in 2 bipedal stances and 2 unipedal stances was assessed with force plates at approximately 2, 5, and 12 months after injury. Single-visit data from participants who were matched for age and served as healthy controls were collected for visual comparison using 95% confidence intervals. Spatial and temporal center-of-pressure (COP) measures were calculated from force plates in the anteroposterior (AP) and mediolateral (ML) directions. Despite improvements in net ML COP postural sway from 2 to 5 months after injury, there were no changes in AP postural sway across recovery. Postural sway in individuals with TBI was higher than normative values at all time points in both directions. Interlimb synchrony did not change across recovery in either direction. TBI weight-bearing asymmetry was lower than normative values at all time points and did not change across recovery. The characteristics of unipedal stance differed between limbs. Sample size was reduced as a result of the inclusion and exclusion criteria; future studies will benefit from a larger sample size. The absence of recovery in ML COP postural sway, interlimb synchrony, and weight-bearing symmetry indicated that reduced ML control may contribute to balance impairments after TBI. These impairments may extend to dynamic balance tasks and may also place individuals with TBI at a higher risk for falls.

Asymmetrical stabilization and mobilization exploited during static single leg stance and goal directed kicking

The motor control properties of the right and left legs are dependent on the stabilization and mobilization features of the motor tasks. The current investigation examined the right and left leg control differences – interlateral asymmetries – during static single leg stance and dynamic goal directed kicking with an emphasis of the asymmetrical stabilization and mobilization components of movements. Ten young, healthy, right-leg preferred individuals with minimal kicking experience completed both tests on each limb. During static single leg stance, participants were requested to stand as still as possible with one leg in contact with a force platform. Interlateral asymmetries of the standing leg were quantified using postural variability measures of the center of pressure (COP) standard deviation in the anterior-posterior (SD-COPAP) and medial-lateral (SD-COPML) directions, resultant COP length and velocity, and 95% COP elliptical area. During dynamic goal directed kicking, participants stood on two adjacent force platforms in a side-by-side foot position and kicked a soccer ball toward three different directions as soon as they received an auditory cue of kicking. Three targets were located −30°, 0° or 30° in front and 3.05 m away from the participants’ midline. Participants kicked the ball toward the targets with each of their feet. The vertical ground reaction force (vGRF) of the kicking leg was used to define the preparation (from above two standard deviations of vGRF baseline to toe-off) and swing (from toe-off to toe-return) phases of dynamic kicking. To determine the presence of interlateral asymmetries during dynamic kicking, the magnitude and timing of the anticipatory postural adjustments (APA) during the preparation phase of kicking were quantified using the lateral net COP (COPnet-ML) time series derived from both force platforms. Postural variability measures of the support leg and the kinematic joint range of motion (JROM) trajectories of the kicking leg were also used to examined interlateral asymmetries. During static stance, no between-leg significance was identified for all dependent measures of COP variability suggesting symmetrical stabilization. During the preparation phase of kicking, both right and left leg kicking exhibited a similar level of APA magnitude, although the left leg kicking was shown to reach its maximum APA magnitude earlier than the right leg. In the support leg role, the right leg showed greater COP variability in the ML direction as compared to the left support leg and greater COP variability was observed when kicking in the ipsilateral direction compared to the center and contralateral directions. For mobilization control, the left kicking leg showed greater JROM displacements at the distal (knee and ankle) joints and reduced JROM primarily with hip frontal plane movements compared to the right kicking leg. The reported interlateral asymmetries during kicking may reflect a behavioral adaptation that results in differential stabilization between the right and left legs. Overall, the findings suggest that novel tasks, such as dynamic goal directed kicking, appear to be more sensitive than static balance in identifying interlateral asymmetries.

A Wearable Neuromuscular Device Reduces ACL Injury Risk in Female Soccer Athletes

Objectives:Female soccer athletes have a three-fold greater risk of sustaining an ACL injury compared with their male counterparts yet only 1 in 5 teams engage in ACL risk reduction programs due to several participation barriers. The purpose of this study was to determine the effects of a wearable neuromuscular (WNM) device on postural control, performance and ACL injury risk in female soccer athletes.Methods:Seventy-nine elite youth and collegiate female soccer athletes (age range: 12-25 y) trained with a WNM device that applied bi-lateral, topical pressure to the medial quadriceps and hamstrings muscles (Topical Gear, Austin, TX). The athletes performed 7-9 weeks of pre-season training with the WNM device consisting of strength and conditioning exercises and on-field team practices (46-64 total hours of exposure). Postural control was measured in 15 athletes with and without the WNM device before and after the training program; and performance was measured in 25 athletes without the WNM device before and after the training program. Postural control was determined from a single-leg landing on a force plate from a horizontal distance normalized to leg length. The athletes were instructed to gain their balance as fast as possible upon landing and remain balanced for 5 seconds. The peak ground reaction forces (GRF) and the medial-lateral, anterior-posterior and net center of pressure (COP) velocities and displacement ranges were calculated during 2 seconds of single-leg stance. Performance measures including speed, power and endurance were measured from the 40 yard dash, vertical jump for height and the Beep test, respectively. A two-way repeated measures ANOVA and post-hoc comparisons were used to compare the postural variables; and t-tests were used to compare the performance tests (p=.05). ACL injury rates, the absolute risk reduction (ARR) and the number needed to treat (NNT) to prevent one ACL injury were calculated between the WNM intervention group and 11 control groups identified from 10 studies in the literature that followed female soccer athletes for an entire soccer season. The treatment effect of the WNM device was determined to be statistically significant at the .05 level if the 95% confidence interval for the ARR of an ACL injury did not include zero.Results:Training with the WNM device demonstrated 18% lower peak medial GRFs (p=.005), 12% lower medial-lateral COP velocities (p=.032) and 18% longer landing phase durations (p=.001). Landing and balance performance with, compared to without, the WNM device demonstrated 2% lower peak vertical GRF (p=.047), 6% lower net COP velocities (p=.044) and 10% lower medial-lateral COP displacements (p=.018). Speed, power and endurance significantly improved 7, 22 and 14% after training with the WNM device (all p<.05). No athletes in the current study sustained an ACL injury during training or over the course of the season. The ARR was on average lowered 1.5% and statistically improved in 9 of the 11 control group comparisons (p<.05) and corresponded to a RRR of 100%. From the NNT analysis, it was determined that 92 female soccer athletes would need to be trained with the WNM device to prevent one ACL injury over the course of one competitive season.Conclusion:Training with a WNM device improved postural control without limiting performance and reduced ACL injury risk in female soccer athletes. Wearable neuromuscular products may provide a solution to the current participation barriers of ACL injury risk reduction programs.

An exploration of the influence of diagonal dissociation and moderate changes in speed on locomotor parameters in trotting horses.

Background. Although the trot is described as a diagonal gait, contacts of the diagonal pairs of hooves are not usually perfectly synchronized. Although subtle, the timing dissociation between contacts of each diagonal pair could have consequences on gait dynamics and provide insight into the functional strategies employed. This study explores the mechanical effects of different diagonal dissociation patterns when speed was matched between individuals and how these effects link to moderate, natural changes in trotting speed. We anticipate that hind-first diagonal dissociation at contact increases with speed, diagonal dissociation at contact can reduce collision-based energy losses and predominant dissociation patterns will be evident within individuals.Methods. The study was performed in two parts: in the first 17 horses performed speed-matched trotting trials and in the second, five horses each performed 10 trotting trials that represented a range of individually preferred speeds. Standard motion capture provided kinematic data that were synchronized with ground reaction force (GRF) data from a series of force plates. The data were analyzed further to determine temporal, speed, GRF, postural, mass distribution, moment, and collision dynamics parameters.Results. Fore-first, synchronous, and hind-first dissociations were found in horses trotting at (3.3 m/s ± 10%). In these speed-matched trials, mean centre of pressure (COP) cranio-caudal location differed significantly between the three dissociation categories. The COP moved systematically and significantly (P = .001) from being more caudally located in hind-first dissociation (mean location = 0.41 ± 0.04) through synchronous (0.36 ± 0.02) to a more cranial location in fore-first dissociation (0.32 ± 0.02). Dissociation patterns were found to influence function, posture, and balance parameters. Over a moderate speed range, peak vertical forelimb GRF had a strong relationship with dissociation time (R = .594; P < .01) and speed (R = .789; P < .01), but peak vertical hindlimb GRF did not have a significant relationship with dissociation time (R = .085; P > 0.05) or speed (R = .223; P = .023).Discussion. The results indicate that at moderate speeds individual horses use dissociation patterns that allow them to maintain trunk pitch stability through management of the cranio-caudal location of the COP. During the hoof-ground collisions, reduced mechanical energy losses were found in hind-first dissociations compared to fully synchronous contacts. As speed increased, only forelimb vertical peak force increased so dissociations tended towards hind-first, which shifted the net COP caudally and balanced trunk pitching moments.

Do quiet standing centre of pressure measures within specific frequencies differ based on ability to recover balance in individuals with stroke?

To determine whether quiet standing measures at specific frequency levels (representative of reactive control) differed between individuals with stroke based on their ability to recover balance (Failed or Successful Responses to external perturbations). Individuals with stroke completed a clinical assessment, including 30s of quiet standing and lean-and-release postural perturbations, at admission to in-patient rehabilitation. Quiet standing centre of pressure (COP) signals were calculated and discrete wavelet decomposition was performed. Net COP amplitude, between-limb synchronization, and ratios of individual-limb COP were determined for each frequency level of interest, and for the non-decomposed signal (all frequency levels). Outcome measures were compared between individuals who exhibited Failed and Successful Responses during (a) unconstrained and (b) encouraged-use lean-and-release trials. Individuals with Failed Responses during the unconstrained lean-and-release trials displayed greater net COP amplitude than those with Successful Responses, specifically within a frequency range of 0.40-3.20Hz. Reduced ability to recover balance among individuals with stroke may be reflected in impaired reactive control of quiet standing. These results provide insight into the mechanism by which reactive control of quiet standing is impaired in individuals with stroke, and may inform assessment and rehabilitation strategies for post-stroke reactive balance control.

Center of Pressure Displacement of Standing Posture during Rapid Movements Is Reorganised Due to Experimental Lower Extremity Muscle Pain.

BackgroundPostural control during rapid movements may be impaired due to musculoskeletal pain. The purpose of this study was to investigate the effect of experimental knee-related muscle pain on the center of pressure (CoP) displacement in a reaction time task condition.MethodsNine healthy males performed two reaction time tasks (dominant side shoulder flexion and bilateral heel lift) before, during, and after experimental pain induced in the dominant side vastus medialis or the tibialis anterior muscles by hypertonic saline injections. The CoP displacement was extracted from the ipsilateral and contralateral side by two force plates and the net CoP displacement was calculated.ResultsCompared with non-painful sessions, tibialis anterior muscle pain during the peak and peak-to-peak displacement for the CoP during anticipatory postural adjustments (APAs) of the shoulder task reduced the peak-to-peak displacement of the net CoP in the medial-lateral direction (P<0.05). Tibialis anterior and vastus medialis muscle pain during shoulder flexion task reduced the anterior-posterior peak-to-peak displacement in the ipsilateral side (P<0.05).ConclusionsThe central nervous system in healthy individuals was sufficiently robust in maintaining the APA characteristics during pain, although the displacement of net and ipsilateral CoP in the medial-lateral and anterior-posterior directions during unilateral fast shoulder movement was altered.

Improved determination of dynamic balance using the centre of mass and centre of pressure inclination variables in a complete golf swing cycle

Golf requires proper dynamic balance to accurately control the club head through a harmonious coordination of each human segment and joint. In this study, we evaluated the ability for dynamic balance during a golf swing by using the centre of mass (COM)–centre of pressure (COP) inclination variables. Twelve professional, 13 amateur and 10 novice golfers participated in this study. Six infrared cameras, two force platforms and SB-Clinic software were used to measure the net COM and COP trajectories. In order to evaluate dynamic balance ability, the COM–COP inclination angle, COM–COP inclination angular velocity and normalised COM–COP inclination angular jerk were used. Professional golfer group revealed a smaller COM–COP inclination angle and angular velocity than novice golfer group in the lead/trail direction (P < 0.01). In the normalised COM–COP inclination angular jerk, the professional golfer group showed a lower value than the other two groups in all directions. Professional golfers tend to exhibit improved dynamic balance, and this can be attributed to the neuromusculoskeletal system that maintains balance with proper postural control. This study has the potential to allow for an evaluation of the dynamic balance mechanism and will provide useful basic information for swing training and prevention of golf injuries.

Effects of Carpal Tunnel Syndrome on adaptation of multi-digit forces to object mass distribution for whole-hand manipulation

BackgroundCarpal tunnel syndrome (CTS) is a compression neuropathy of the median nerve that results in sensorimotor deficits in the hand. Until recently, the effects of CTS on hand function have been studied using mostly two-digit grip tasks. The purpose of this study was to investigate the coordination of multi-digit forces as a function of object center of mass (CM) during whole-hand grasping.MethodsFourteen CTS patients and age- and gender-matched controls were instructed to grasp, lift, hold, and release a grip device with five digits for seven consecutive lifts while maintaining its vertical orientation. The object CM was changed by adding a mass at different locations at the base of the object. We measured forces and torques exerted by each digit and object kinematics and analyzed modulation of these variables to object CM at object lift onset and during object hold. Our task requires a modulation of digit forces at and after object lift onset to generate a compensatory moment to counteract the external moment caused by the added mass and to minimize object tilt.ResultsWe found that CTS patients learned to generate a compensatory moment and minimized object roll to the same extent as controls. However, controls fully exploited the available degrees of freedom (DoF) in coordinating their multi-digit forces to generate a compensatory moment, i.e., digit normal forces, tangential forces, and the net center of pressure on the finger side of the device at object lift onset and during object hold. In contrast, patients modulated only one of these DoFs (the net center of pressure) to object CM by modulating individual normal forces at object lift onset. During object hold, however, CTS patients were able to modulate digit tangential force distribution to object CM.ConclusionsOur findings suggest that, although CTS did not affect patients’ ability to perform our manipulation task, it interfered with the modulation of specific grasp control variables. This phenomenon might be indicative of a lower degree of flexibility of the sensorimotor system in CTS to adapt to grasp task conditions.

Interleg Coordination in Quiet Standing: Influence of Age and Visual Environment on Noise and Stability

ABSTRACT The authors reexamined reported effects of age, illumination, and stationary visible structure on the net center of pressure (COP) derived from dual, side-by-side force plates (J. Kinsella-Shaw, S. Harrison, C. Colon-Semenza, & M. Turvey, 2006) from the perspective of axial postural control. They questioned how left and right COP x (t), COP y (t), and vertically oriented ground reactive force, GRF z (t), coordinated during quiet standing. The Cross- recurrence Quantification (CRQ) revealed that coordination was primarily between fluctuations of similar direction, with coordination of left and right COP y (t) (anteroposterior fluctuations) dominant. CRQ also revealed that (a) illumination and structure affected the interlimb dynamics of older (M age = 72.2 ± 4.90 years) participants more than their younger (M age = 22.8 ± 0.83 years) counterparts, and (b) older participants exhibited greater interlimb entrainment (dynamical stability) in the presence of greater interlimb noise.

Effect of Hinged Ankle-Foot Orthoses on Standing Balance Control in Children with Bilateral Spastic Cerebral Palsy

PurposeTo identify the characteristics of static standing balance and its postural control mechanisms during quiet side-by-side standing and the changes in these measures whilst wearing hinged ankle-foot orthoses (AFOs) in children with bilateral spastic cerebral palsy (CP).Materials and MethodsTwenty-one children with bilateral spastic CP (6.10 ± 1.09 year-old) and 22 typically developing (TD) children (5.64 ± 0.49 year-old) were recruited. Pressure data were recorded while subjects with or without AFOs stood on dual force platforms and net body center of pressure (CoP) coordinates were calculated from this data. Net body CoP was traced for measuring mediolateral (ML) and anteroposterior (AP) displacement and path length per second. Correlation coefficients between parameters representing ankle, hip, and transverse body rotation strategies were also analyzed.ResultsML and AP displacement and path length per second of the CoP trajectory were higher in children with CP compared to TD children (p < 0.05). There were no significant improvements in these parameters whilst wearing hinged AFOs. Compared to TD children, children with CP used less ankle strategy though more hip and transverse rotation strategies for postural control during quiet standing. Whilst wearing hinged AFOs, the contribution of ankle strategy was significantly increased for ML balance control in children with CP (p < 0.05).ConclusionHinged AFOs for children with CP may be helpful in improving the postural control mechanisms but not the postural stability in quiet side-by-side standing.

The control of upright stance in young, elderly and persons with Parkinson's disease

The aims of the present study are twofold: (1) to compare the postural control mechanisms of young and elderly people as well as in Parkinson's disease (PD) patients during quiet standing and (2) to assess the impact of a stooped posture on these mechanisms. All subjects were required to maintain both a side-by-side and a 45° foot position. Elderly subjects performed a third condition where they were requested to mimic the stooped posture as adopted by PD subjects. The net centre of pressure (COP net) and centre of mass (COM) profiles in the anterior/posterior (A/P) and medial/lateral (M/L) planes were analyzed. The COP net signal was recorded from two force plates and was categorized in two mechanisms: an ankle mechanism (COP c ) and a load/unload hip mechanism (COP v ). The results showed similar postural control mechanisms in young, elderly and PD subjects. When the feet were side-by-side, the COP net was controlled by the ankle plantar/dorsiflexors (COP c ) in the A/P direction, while by the hip abductor/adductors (COP v ) controlled in the M/L direction. When the feet were in the 45° position, both the ankle and hip mechanisms contributed to the COP net. However, the PD subjects showed significant smaller RMS amplitudes compared to the elderly people in the 45° foot position and in the stooped posture. These findings suggest that PD subjects resort to a stiffening strategy to control their balance in postural tasks that imply a mixed control (ankle and hip mechanisms) but have adapted to their stooped posture.

The Effect of Trunk-Flexed Postures on Balance and Metabolic Energy Expenditure During Standing

This study analyzed force plate, kinematic, and metabolic energy data of 14 able-bodied subjects standing statically with upright and trunk-flexed postures. To explore the effect of trunk-flexed postures on balance and metabolic energy expenditure during standing. Abnormal trunk posture often occurs in the presence of spinal deformities, such as lumbar flatback. It is unclear whether alterations in trunk posture affect energy expenditure and the location of the body's center of mass in the transverse plane (BCOMtrans) during standing. Kinematic, kinetic, and energy expenditure data were collected with upright trunk alignment and with 25 degrees +/- 7 degrees and 50 degrees +/- 7 degrees of trunk flexion from the vertical. The mean location of the BCOMtrans was estimated from the net center of pressure (COP), which is a weighted average of the COP beneath both feet. The fore-aft position of the net COP under the base of support was not significantly different between postures (P < 0.08). At each posture, the net COP was located 16% of the foot length anterior to the ankle joint centers. However, with increasing trunk flexion, there was a significant increase in oxygen consumption rate (P < 0.001 for all postures). Compensatory actions, such as ankle plantarflexion and hip flexion, allowed the mean position of the net COP to remain within a narrowly defined region irrespective of trunk posture. Changes in muscle activity associated with a trunk-flexed posture and the associated compensations likely contributed to the increased energy expenditure.