Anterior-posterior Center Of Pressure Research Articles

Anterior-Posterior Center of Pressure Is Associated With Knee Extensor Moment During Landing After Anterior Cruciate Ligament Reconstruction.

A reduced knee extensor moment (KEM) in the involved limb and asymmetry in the KEM during landing tasks are observed after anterior cruciate ligament reconstruction (ACLR). There is limited information about the association of kinetic and kinematic parameters with the KEM during landing after ACLR. This study investigated the association of the anterior-posterior center of pressure (AP-COP) position, vertical ground reaction force (VGRF), and lower limb joint angles with the KEM during landing in female athletes following ACLR. Cross-sectional study. Twenty-two female athletes who underwent ACLR performed a drop vertical jump at 7.9 (1.7)months after surgery. We evaluated the KEM, AP-COP position, VGRF, and sagittal plane hip, knee, and ankle angles using a 3-dimensional motion analysis system with force plates. The peak KEM in the involved limb was significantly smaller than that in the uninvolved limb during landing (1.43 [0.33]N·m/kg/m vs 1.84 [0.41]Nm/kg/m, P = .001). The VGRF in the involved limb was significantly smaller than that in the uninvolved limb (11.9 [2.3]N/kg vs 14.6 [3.5]N/kg, P = .005). The limb symmetry index of the KEM was predicted by that of the VGRF (P < .001, R2 = .621, β = 0.800). The KEM was predicted by the AP-COP position in the involved limb (P = .015, R2 = .227, β = 0.513) and by the VGRF in the uninvolved limb (P = .018, R2 = .213, β = 0.500). No significant correlation was noted between the KEM and the lower limb joint angles. The AP-COP position and VGRF were associated with the KEM during landing. Evaluating the VGRF and AP-COP position, not the lower limb joint angles, may contribute to understanding the KEM during double-leg landing after ACLR in the clinical setting.

Clubfoot patients show more anterior-posterior displacement during one-leg-standing and less ankle power and plantarflexor moment during one-leg-hopping than typically developing children

BackgroundClubfoot patients show good-to-excellent foot correction after the Ponseti method. Nevertheless, underlying functional problems that limit motor abilities such as one-leg-standing and one-leg-hopping still persist. These restrictions have been proposed to arise due to problems with maintaining balance and the limited force-generating capacity of clubfoot patients. More insight is needed to understand the underlying limiting factors to improve overall motor ability in clubfoot patients. Research questionThe aim of this study was to determine the differences between clubfoot patients and typically developing children (TDC) in force and balance parameters during walking, one-leg-standing and hopping. MethodsThree-dimensional motion analysis was performed in 19 TDC and 16 idiopathic Ponseti-treated clubfoot patients between 5–9 years old. Kinematic and kinetic parameters were calculated during walking and one-leg-hopping. To describe the balance parameters, center of pressure (CoP) data was assessed during walking, one-leg-hopping and one-leg-standing. Mean group values were calculated and compared using nonparametric statistical tests. A general linear model with repeated measures was used to determine which activity showed the largest group differences. ResultsClubfoot patients showed lower peak plantarflexor moment and peak ankle power absorption and generation during one-leg-hopping compared to TDC. Furthermore, clubfoot patients showed a lower hop length and velocity than TDC. The difference in peak plantarflexor moment and ankle power between the study groups was larger during one-leg-hopping than during walking. Finally, clubfoot patients showed a higher anterior-posterior CoP range during one-leg-standing. SignificanceDeviations in force parameters seemed to limit one-leg-hopping in clubfoot patients, and impaired anterior-posterior static balance was thought to be the underlying cause of problems with one-leg-standing. Furthermore, one-leg-hopping was more sensitive to distinguish between clubfoot patients and TDC than walking. Individualized physiotherapy targeting static balance and force parameters, with extra emphasis on including eccentric contractions, might improve the overall motor abilities of clubfoot patients.

Concurrent activation potentiation improves lower-limb maximal strength but not dynamic balance control in rugby players.

Concurrent activation potentiation (CAP) increases athletic performance by activating muscles not involved in the performed activity. Among the CAP strategies, jaw clenching is the most practical to implement in sports contexts. Muscle strength and balance control are essential among rugby players to cope tackles. Besides combat sports, mouthguard has become mandatory also in rugby. Therefore, this study aimed to understand whether mouthguard jaw-clenching could improve rugby players' dynamic balance and quadriceps isometric strength. Thirteen rugby players were tested under maximal-bite (MB) and no-bite (NB) conditions. During standing balance tests, an electro-actuated platform with a force plate screwed on it allowed for the perturbation of the support base of the rugby players. A verbal signal warned the subject that the perturbation was coming, mentally recalling an in-field expected collision. In the first 2.5s window after the perturbation, the center of pressure (CoP) displacement and mean velocity were measured. The first peak, the maximal oscillations, and the standard deviation of the anterior-posterior CoP trajectory were calculated within the same time window. In the isometric leg-extension test, a custom-built chair instrumented with a uni-axial load cell allowed to collect the maximal strength and rate of force development (RFD). Mouthguard jaw-clenching did not affect CoP-related parameters but increased maximal strength (p < 0.05) and RFD (0-50ms: p < 0.01; 50-100ms: p < 0.001; 100-150ms: p < 0.05) in the isometric leg-extension test. Mouthguard jaw-clenching alone could be useful to increase lower-limb maximal isometric strength and RFD but did not improve dynamic balance performance in a sport-oriented postural balance test.

DFA as a window into postural dynamics supporting task performance: does choice of step size matter?

Introduction: Detrended Fluctuation Analysis (DFA) has been used to investigate self-similarity in center of pressure (CoP) time series. For fractional gaussian noise (fGn) signals, the analysis returns a scaling exponent, DFA-α, whose value characterizes the temporal correlations as persistent, random, or anti-persistent. In the study of postural control, DFA has revealed two time scaling regions, one at the short-term and one at the long-term scaling regions in the diffusion plots, suggesting different types of postural dynamics. Much attention has been given to the selection of minimum and maximum scales, but the choice of spacing (step size) between the window sizes at which the fluctuation function is evaluated may also affect the estimates of scaling exponents. The aim of this study is twofold. First, to determine whether DFA can reveal postural adjustments supporting performance of an upper limb task under variable demands. Second, to compare evenly-spaced DFA with two different step sizes, 0.5 and 1.0 in log2 units, applied to CoP time series. Methods: We analyzed time series of anterior-posterior (AP) and medial-lateral (ML) CoP displacement from healthy participants performing a sequential upper limb task under variable demand. Results: DFA diffusion plots revealed two scaling regions in the AP and ML CoP time series. The short-term scaling region generally showed hyper-diffusive dynamics and long-term scaling revealed mildly persistent dynamics in the ML direction and random-like dynamics in the AP direction. There was a systematic tendency for higher estimates of DFA-α and lower estimates for crossover points for the 0.5-unit step size vs. 1.0-unit size. Discussion: Results provide evidence that DFA-α captures task-related differences between postural adjustments in the AP and ML directions. Results also showed that DFA-α estimates and crossover points are sensitive to step size. A step size of 0.5 led to less variable DFA-α for the long-term scaling region, higher estimation for the short-term scaling region, lower estimate for crossover points, and revealed anomalous estimates at the very short range that had implications for choice of minimum window size. We, therefore, recommend the use of 0.5 step size in evenly spaced DFAs for CoP time series similar to ours.

Postural threat increases sample entropy of postural control.

Postural threat elicits modifications to standing balance. However, the underlying neural mechanism(s) responsible remain unclear. Shifts in attention focus including directing more attention to balance when threatened may contribute to the balance changes. Sample entropy, a measure of postural sway regularity with lower values reflecting less automatic and more conscious control of balance, may support attention to balance as a mechanism to explain threat-induced balance changes. The main objectives were to investigate the effects of postural threat on sample entropy, and the relationships between threat-induced changes in physiological arousal, perceived anxiety, attention focus, sample entropy, and traditional balance measures. A secondary objective was to explore if biological sex influenced these relationships. Healthy young adults (63 females, 42 males) stood quietly on a force plate without (No Threat) and with (Threat) the expectation of receiving a postural perturbation (i.e., forward/backward support surface translation). Mean electrodermal activity and anterior-posterior centre of pressure (COP) sample entropy, mean position, root mean square, mean power frequency, and power within low (0-0.05 Hz), medium (0.5-1.8 Hz), and high-frequency (1.8-5 Hz) components were calculated for each trial. Perceived anxiety and attention focus to balance, task objectives, threat-related stimuli, self-regulatory strategies, and task-irrelevant information were rated after each trial. Significant threat effects were observed for all measures, except low-frequency sway. Participants were more physiologically aroused, more anxious, and directed more attention to balance, task objectives, threat-related stimuli, and self-regulatory strategies, and less to task-irrelevant information in the Threat compared to No Threat condition. Participants also increased sample entropy, leaned further forward, and increased the amplitude and frequency of COP displacements, including medium and high-frequency sway, when threatened. Males and females responded in the same way when threatened, except males had significantly larger threat-induced increases in attention to balance and high-frequency sway. A combination of sex and threat-induced changes in physiological arousal, perceived anxiety, and attention focus accounted for threat-induced changes in specific traditional balance measures, but not sample entropy. Increased sample entropy when threatened may reflect a shift to more automatic control. Directing more conscious control to balance when threatened may act to constrain these threat-induced automatic changes to balance.

Cortical potentials time-locked to discrete postural events during quiet standing are facilitated during postural threat exposure.

During unperturbed bipedal standing, postural control is governed primarily by subcortical and spinal networks. However, it is unclear if cortical networks begin to play a greater role when stability is threatened. This study investigated how initial and repeated exposure to a height-related postural threat modulates cortical potentials time-locked to discrete centre of pressure (COP) events during standing. Twenty-seven young adults completed a series of 90-s standing trials at LOW (0.8m above the ground, away from edge) and HIGH (3.2m above the ground, at edge) threat conditions. Three LOW trials were completed before and after 15 consecutive HIGH trials. Participants stood on a force plate while electroencephalographic (EEG) activity was recorded. To examine changes in cortical activity in response to discrete postural events, prominent forward and backward peaks in the anterior-posterior COP time series were identified. EEG data were waveform-averaged to these events and the amplitude of event-related cortical activity was calculated. At the LOW condition, event-related potentials (ERPs) were scarcely detectable. However, once individuals stood at the HIGH condition, clear ERPs were observed, with more prominent potentials being observed for forward (edge-directed), compared to backward, COP events. Since forward COP peaks accelerate the centre of mass away from the platform edge, these results suggest there is intermittent recruitment of cortical networks that may be involved in the detection and minimization of postural sway toward a perceived threat. This altered cortical engagement appears resistant to habituation and may contribute to threat-related balance changes that persist following repeated threat exposure. KEY POINTS: While standing balance control is regulated primarily by subcortical and spinal processes, it is unclear if cortical networks play a greater role when stability is threatened. This study examined how cortical potentials time-locked to prominent peaks in the anterior-posterior centre of pressure (COP) time series were modulated by exposure to a height-related postural threat. While cortical potentials recorded over the primary sensorimotor cortices were scarcely detectable under non-threatening conditions, clear cortical potentials were observed when individuals stood under conditions of height-related threat. Cortical potentials were larger in response to COP peaks directed toward, compared to away from, the platform edge, and showed limited habituation with repeated threat exposure. Since forward COP peaks accelerate the centre of mass away from the platform edge, these findings suggest that when balance is threatened, there is intermittent recruitment of cortical networks, which may minimize the likelihood of falling in the direction of a perceived threat.

Precision aiming performance with the paretic upper limb is associated with center of pressure patterns in individuals with chronic stroke

BackgroundIndividuals with stroke commonly demonstrate upper-limb sensorimotor impairments. Upper-limb tasks occur against a background level of postural control and thus require a flexible postural control system to facilitate performance. Anterior precision aiming tasks, for example, benefit from lower medial-lateral (ML) center of pressure (COP) fluctuations (where increased fluctuations erode performance) relative to anterior-posterior (AP) fluctuations (where increased fluctuations do not strongly influence performance). After stroke, individuals may compensate for upper-limb impairments by increasing trunk movement which increases overall COP fluctuations and thus may make it more difficult to modulate COP in a task-sensitive manner. Research questionDo upper-limb task demands modulate COP movement patterns after stroke? MethodsIn this cross-sectional study, adults with chronic stroke (n = 23) and unilateral upper-limb impairments were immersed in a virtual environment displaying an anterior target. Participants aimed to maintain the position of a virtual laser pointer (via handheld controller) in the target with each hand. COP was concurrently recorded. Mixed effects models and correlations were used to detect differences in COP patterns between limbs and movement planes and evaluate associations between task performance and COP patterns, respectively. ResultsParticipants showed greater COP standard deviation and regularity in the AP compared to the ML direction. The magnitude of difference between AP and ML COP metrics was greater using the nonparetic limb. Task performance was moderately and positively associated with task-sensitive COP patterns (i.e., higher AP:ML ratios of COP metrics) using the paretic upper limb. Participants consistently demonstrated high levels of task performance and task-sensitive COP movement patterns using the nonparetic limb. SignificanceImpairments in postural control after stroke may be related to the upper limb used. It is important to recognize the role of directional COP variability and regularity in the context of a task goal after stroke.

Changes in postural sway during upright stance after short-term lower limb physical inactivity: A prospective study.

Previous studies have reported that motor behavior is affected by short-term physical inactivity using cast immobilization; however, the effects of inactivity on postural sway are not well-understood. This study aimed to investigate the effects of short-term lower limb disuse on postural sway in the upright position after cast removal. Twenty-two healthy young adults were enrolled, and each participant’s lower limb on one side was fixed with a soft bandage and medical splint made from metal and soft urethane for 10 h. Fluctuations in the center of pressure (COP) were measured before and after immobilization; the total trajectory length, mean velocity, COP root mean square (RMS) area, mean medial-lateral (M-L) COP, and mean anterior-posterior (A-P) COP were selected as evaluation parameters. Compared with the postural sway before cast application, we noted an increase and shift (from the fixed to the nonfixed side) in the postural sway after cast removal. Our results therefore suggest that short-term disuse may cause acute changes in COP movements during quiet standing. Moreover, patients may maintain their standing posture by adopting a compensatory strategy involving lateral control, similar to individuals with stroke and patients who have undergone total knee arthroplasty.

102. An introductory investigation of standing postural control ‘error’ and its relation to balance in adult spinal deformity surgery patients

102. An introductory investigation of standing postural control ‘error’ and its relation to balance in adult spinal deformity surgery patients

Effects of Changing Center of Pressure Position on Knee and Ankle Extensor Moments During Double-Leg Squatting.

The effects of changes in the anterior-posterior center of pressure (AP-COP) position on the lower limb joint moments during double-leg squatting remain unclear. The purpose of this study was to determine the effects of AP-COP positional changes on the hip, knee, and ankle extensor moments during double-leg squatting. Sixteen male participants (22.1 ± 1.5 years) performed double-leg squatting under two conditions (anterior and posterior COP conditions) with visual feedback on their COP positions. Kinematics and kinetics were analyzed using a three-dimensional motion analysis system and force plates. The hip, knee and ankle flexion angles and extensor moments at peak vertical ground reaction force were compared between the two conditions using paired t tests. The COP position was 53.5 ± 2.4% of the foot length, starting from the heel, under the anterior condition and 44.4 ± 2.1% under the posterior condition (P < 0.001). The knee extensor moment was significantly smaller under the anterior than the posterior COP condition (P = 0.003, 95% confidence interval (CI) -0.087 to -0.021 Nm/kg/m), while the ankle extensor moment significantly larger under the anterior COP condition than under the posterior COP condition (P < 0.001, 95% CI 0.113 to 0.147 Nm/kg/m). There was no significant difference in hip extensor moment (P = 0.431). The ankle dorsiflexion angle was significantly larger under the anterior than the posterior COP condition (P = 0.003, 95% CI 0.6 to 2.6°), while there was no difference in trunk, hip, or knee flexion angle. The present results indicate that changes in the AP-COP position mainly affect the ankle and knee extensor moments during double-leg squatting, while the effect on the lower limb joint and trunk flexion angles was limited. Visual feedback on the AP-COP position could be useful for modifying the ankle and knee extensor moments during double-leg squatting.

Postural Control Differences between Patients with Posterior Tibial Tendon Dysfunction and Healthy People during Gait.

Background: Patients with posterior tibial tendon dysfunction (PTTD) may exhibit postural instability during walking likely due to a loss of medial longitudinal arch, abnormal foot alignment, and pain. While many studies have investigated gait alterations in PTTD, there is no understanding of dynamic postural control mechanisms in this population during gait, which will help guide rehabilitation and gait training programs for patients with PTTD. The purpose of the study was to assess dynamic postural control mechanisms in patients with stage II PTTD as compared to age and gender matched healthy controls. Methods: Eleven patients with stage II PTTD (4 males and 7 females; age 59 ± 1 years; height 1.66 ± 0.12 m; mass 84.2 ± 16.0 kg) and ten gender and age matched controls were recruited in this study. Participants were asked to walk along a 10 m walkway. Ten Vicon cameras and four AMTI force platforms were used to collect kinematic and center of pressure (COP) data while participants performed gait. To test differences between PTTD vs. control groups, independent t-tests (set at α < 0.05) were performed. Results: Patients with PTTD had significantly higher double stance ratio (+23%) and anterior-posterior (AP) time to contact (TTC) percentage (+16%) as compared to healthy control. However, PTTD had lower AP COP excursion (−19%), AP COP velocity (−30%), and medial-lateral (ML) COP velocity (−40%) as compared to healthy controls. Mean ML COP trace values for PTTD were significantly decreased (−23%) as compared to controls, indicating COP trace for PTTD tends to be closer to the medial boundary than controls during single-support phase of walking. Conclusion: PTTD patients showed more conservative and cautious postural strategies which may help maintain balance and reduce the need for postural adjustment during PTTD gait. They also showed more medially shifted COP patterns than healthy controls during single-support phase of walking. Dynamic postural control outcomes could be used to develop effective gait training programs aimed at alleviating a medial shift of COP (everted foot) for individuals with PTTD in order to improve their functionality and gait efficiency.

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.

Effects of age, sex and task on postural sway during quiet stance

BackgroundPostural sway during quiet standing has been shown as a useful task to assess risk of falling in older adults. While the risk of falling is consistently reported to be higher in older females than males, the sex-related differences in postural sway are not consistent across the studies. Research questionWhat are the effects of age and sex on postural sway during quiet standing during different stance conditions? MethodsWe examined the effects of age (40 young and 34 older adults), sex (37 males and 37 females), and their interaction on the postural sway during different stance conditions. We compared the center of pressure (CoP) velocity, amplitude and frequency during parallel (eyes open and eyes closed) and semi-tandem (eyes open) stances. ResultsOur results suggest that postural sway is similar between sexes in young participants, while older males exhibit larger postural sway than older female participants (10/21 outcomes). Older female participants exhibited lower CoP amplitude (but larger total and anterior-posterior CoP velocity) compared to young female participants. We also found that the increase in the postural sway with increasing task difficulty is more pronounced in older vs. young adults. SignificanceThis study shows that ageing-related changes in postural sway are sex- and task-specific. Researchers and clinicians need to be aware of these effects when comparing groups or monitoring changes in time.

Changes in Center of Pressure after Robotic Exoskeleton Gait Training in Adults with Acquired Brain Injury.

Acquired brain injury (ABI) resulting in hemiplegia, is one of the leading causes of gait and balance deficits in adults. Gait and balance deficits include reduced momentum for forward progression, reduced step length, increased spatial and temporal asymmetry, and decreased speed; resulting in reduced functional ambulation, activities of daily living, and quality of life. Wearable lower extremity robotic exoskeletons (REs) are becoming an effective method for gait neurorehabilitation in individuals with ABI. REs can provide high dose, consistent, goal-directed repetition of movements as well as balance & stability for individuals with ABI. The objective of this study is to understand the effect of RE gait training using center of pressure (COP) displacement, temporal & spatial parameters, and functional outcomes for individuals with ABI. The results from this investigation show improved anterior-posterior COP displacement & rate of progression, spatial symmetry, step length, walking speed, and decreased time during the gait cycle. These preliminary results suggest that high dose, repetitive gait training using robotic exoskeletons has the potential to induce recovery of function in adults diagnosed with ABI.

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

Assistive 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. Is postural sway control in single limb stance during a balance perturbance affected by walker type? Twenty-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. The 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. The 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.

Validity and reliability of standing balance control measurement on the left unilateral spatial neglect model

BACKGROUND: The present study developed a head-mounted display with the visual direction of a web camera modified to the right as a left unilateral spatial neglect (USN) model with respect to postural balance control. AIM: We aimed to estimate the validity and reliability of center of pressure (CoP) measurements in static standing balance (SSB) and dynamic standing balance (DSB) of healthy participants were using the USN model and to examine whether this model's use influenced postural balance control. METHOD: A portable CoP force plate was used to quantify postural balance control in 64 healthy participants as the model. The CoP displacement of the non-USN and USN models in the medial-lateral (ML) and anterior-posterior (AP) planes, CoP length, and bilateral load ratio in SSB and DSB to the right (R) and left (L) were evaluated. RESULTS: Regression analysis indicated that most CoP measurements have excellent concurrent validity. Bland–Altman plots showed good agreement between the non-USN and USN models in the CoP measurements. Test-retest reliability estimation between two times measurements varied in the frontal and sagittal planes. A Comparison of the results demonstrated that the CoP-AP and CoP length changed (-1.40% and 7.67%, respectively) significantly in SSB (P&lt;0.05). Moreover, the CoP-AP changed very significantly in DSB-R and DSB-L (-1.50% and 1.86%, respectively) in opposite directions (P&lt;0.01) when the subjects performed as the model. CONCLUSION: CoP measurements are valid and reliable to quantify standing balance control in both non-USN and USN models that appear to modulate changes in postural adaptation and adjustment.

The association of reactive balance control and spinal curvature under lumbar muscle fatigue.

BackgroundAlthough low back fatigue is an important intervening factor for physical functioning among sedentary people, little is known about its possible significance in relation to the spinal posture and compensatory postural responses to unpredictable stimuli. This study investigates the effect of lumbar muscle fatigue on spinal curvature and reactive balance control in response to externally induced perturbations.MethodsA group of 38 young sedentary individuals underwent a perturbation-based balance test by applying a 2 kg load release. Sagittal spinal curvature and pelvic tilt was measured in both a normal and Matthiass standing posture both with and without a hand-held 2 kg load, and before and after the Sørensen fatigue test.ResultsBoth the peak anterior and peak posterior center of pressure (CoP) displacements and the corresponding time to peak anterior and peak posterior CoP displacements significantly increased after the Sørensen fatigue test (all at p < 0.001). A lumbar muscle fatigue led to a decrease of the lumbar lordosis in the Matthiass posture while holding a 2 kg load in front of the body when compared to pre-fatigue conditions both without a load (p = 0.011, d = 0.35) and with a 2 kg load (p = 0.000, d = 0.51). Also the sacral inclination in the Matthiass posture with a 2 kg additional load significantly decreased under fatigue when compared to all postures in pre-fatigue conditions (p = 0.01, d = 0.48). Contrary to pre-fatigue conditions, variables of the perturbation-based balance test were closely associated with those of lumbar curvature while standing in the Matthiass posture with a 2 kg additional load after the Sørensen fatigue test (r values in range from −0.520 to −0.631, all at p < 0.05).ConclusionThese findings indicate that lumbar muscle fatigue causes changes in the lumbar spinal curvature and this is functionally relevant in explaining the impaired ability to maintain balance after externally induced perturbations. This emphasizes the importance for assessing both spinal posture and reactive balance control under fatigue in order to reveal their interrelations in young sedentary adults and predict any significant deterioration in later years.

Trunk kinematics and muscle activation patterns during stand-to-sit movement and the relationship with postural stability in aging

BackgroundStand-to-sit (StandTS) movement is an important functional activity that can be challenging for older adults due to age-related changes in neuromotor control. Although trunk flexion, eccentric contraction of the rectus femoris (RF), and coordination of RF and biceps femoris (BF) muscles are important to the StandTS task, the effects of aging on these and related outcomes are not well studied. Research questionWhat are the age-related differences in trunk flexion, lower extremity muscle activation patterns, and postural stability during a StandTS task and what is the relationship between these variables? MethodsTen younger and ten older healthy adults performed three StandTS trials at self-selected speeds. Outcomes included peak amplitude, peak timing, burst duration, and onset latency of electromyography (EMG) activity of the RF and BF muscles, trunk flexion angle and angular velocity, whole body center of mass (CoM) displacement, center of pressure (CoP) velocity, and ground reaction force (GRF). ResultsThere were no age-related differences in weight-bearing symmetry, StandTS and trunk flexion angular velocity, or BF activity. In both groups, EMG peak timing of RF was preceded by BF. Compared to younger adults, older adults demonstrated shorter RF EMG burst duration, reduced trunk flexion, and reduced stability as indicated by the longer duration in which CoM was maintained beyond the posterior limit of base of support (BoS), greater mean anterior-posterior CoP velocity and larger standard deviation of CoM vertical acceleration during StandTS with smaller vertical GRF immediately prior to StandTS termination. Trunk flexion angle and RF EMG burst duration correlated with stability as measured by the duration in which the CoM stayed within the BoS. SignificanceDecreased trunk flexion and impaired eccentric control of the RF are associated with StandTS instability in aging and suggest the importance of including StandTS training as a part of a comprehensive balance intervention.

Bidirectional causal control in the dynamics of handstand balance

The aim of this study was to identify motor control solutions associated with the ability to maintain handstand balance. Using a novel approach, we investigated the dynamical interactions between centre of pressure (CoP) and centre of mass (CoM) motion. A gymnastics cohort was divided into a ‘less skilled’ group, who held handstands for 4–6 s, and a ‘more skilled’ group, who held handstands in excess of 10 s. CoP–CoM causality was investigated in anterior–posterior (AP) and medio-lateral (ML) directions, in addition to time–space, time–frequency and Hurst Exponent (H) analyses. Lower AP CoP to CoM causal drive and lower H values (> 0.6) indicated the more skilled gymnasts were less reliant on CoP mechanics to drive CoM motion. More skilled performance demonstrated greater adaptability through use of reactive, as opposed to anticipatory, control strategies. Skilled performers additionally exploited mechanical advantages in ML (e.g. a wider base of support), compared to the less skilled athletes. A multiple regression analysis revealed H and frequency domain measures to be better predictors of handstand balance duration than time–space domain measures. The study findings highlight the advantage of an adaptable motor control system with a directional profile, and provide new insight into the clear, measurable footprint of CoP on the dynamics of CoM.

A systematic review of center of pressure measures to quantify gait changes in older adults.

Measures of gait center of pressure (COP) can be recorded using simple available technologies in clinical settings and thus can be used to characterize gait quality in older adults and its relationship to falls. The aim of this systematic review was to investigate the association between measures of gait COP and aging and falls. A comprehensive search of electronic databases including MEDLINE, Embase, Cochrane Central Register of Controlled Trials, CINAHL (EBSCO), Ageline (EBSCO) and Scopus was performed. The initial search yielded 2809 papers. After removing duplicates and applying study inclusion/exclusion criteria, 34 papers were included in the review. Gait COP has been examined during three tasks: normal walking, gait initiation, and obstacle negotiation. The majority of studies examined mean COP position and velocity as outcome measures. Overall, gait in older adults was characterized by more medial COP trajectory in normal walking and lower average anterior-posterior and medio-lateral COP displacements and velocity in both gait initiation and obstacle crossing. Moreover, findings suggest that Tai chi training can enhance older adults' balance control during gait initiation as demonstrated by greater COP backward, medial and forward shift in all three phases of gait initiation. These findings should be interpreted cautiously due to inadequacy of evidence as well as methodological limitations of the studies such as small sample size, limited numbers of 'fallers', lack of a control group, and lack of interpretation of COP outcomes with respect to fall risk. COP measures can be adopted to assess fall-related gait changes in older adults but more complex measures of COP that reveal the dynamic nature of COP behavior in step-to-step variations are needed to adequately characterize gait changes in older adults.