The role of plantar cutaneous sensation in unperturbed stance

Postural control in 13-year-old soccer players

To evaluate the effect of early systematic soccer training on postural control we measured center-of-pressure (COP) variability, range, mean velocity and frequency in bipedal quiet stance with eyes open (EO) and closed (EC) in 44 boys aged 13 (25 boys who practiced soccer for 5–6 years and 19 healthy boys who did not practice sports). The soccer players had better stability, particularly in the medial–lateral plane (M/L); their COP variability and range were lower than in controls in both EO (p < 0.05) and EC (p < 0.0005) condition indicating that the athletes were less dependent on vision than non-athletes. Improved stability of athletes was accompanied by a decrease in COP frequency (p < 0.001 in EO, and p < 0.04 in EC) which accounted for lower regulatory activity of balance system in soccer players. The athletes had lower COP mean velocity than controls (p < 0.0001 in both visual condition), with larger difference in the M/L than A/P plane (p < 0.00001 and p < 0.05, respectively). Postural behavior was more variable within the non-athletes than soccer players, mainly in the EC stances (p < 0.005 for all COP parameters). We conclude that: (1) soccer training described was efficient in improving the M/L postural control in young boys; (2) athletes developed specific postural strategies characterized by decreased COP frequency and lower reliance on vision.

Disruption of cutaneous feedback alters magnitude but not direction of muscle responses to postural perturbations in the decerebrate cat

Quadrupeds and bipeds respond to horizontal perturbations of the support surface with muscular responses that are broadly tuned and directionally sensitive. Since the discovery of this directional sensitivity, interest has turned toward the critical sensory systems necessary to generate these responses. We hypothesize that cutaneous feedback affects the magnitude of muscle responses to postural perturbation but has little effect on the directionality of the muscle response. We developed a modified premammillary decerebrate cat preparation to evaluate the sensory mechanisms driving this directionally sensitive muscle activation in response to support surface perturbation. This preparation allows us the flexibility to isolate the proprioceptive (cutaneous and muscle receptors) system from other sensory influences. We found that loss of cutaneous feedback leads to a significant loss in background activity causing a smaller muscular response to horizontal perturbations. However, the directional properties of the muscular responses remained intact.

The effect of textured insoles on gait patterns of people with multiple sclerosis

BACKGROUND

Somatosensory deficit is a common feature of MS. One method serving to combat impaired plantar sensation may be to provide enhanced sensory feedback from the sole of the foot by changing the characteristics of a shoe sole or surface. This study aimed to inspect the effect of textured insoles on gait patterns in a group of MS patients.

METHODS

14 patients with MS and 10 healthy control subjects were recruited for this study. Plantar sensation was evaluated using Semmes-Weinstein monofilaments. Kinematic, kinetic and EMG gait data were collected for MS patients walking with flat shoes only and again with shoes and a textured insole in contact with the sole of patients' feet.

RESULTS

A reduction in plantar sensation was identified in the MS patient group compared to the control group. Wearing the textured insoles there was a significant increase in hip and knee sagittal plane excursion, maximum ankle dorsiflexion, knee flexion and in peak acceleration ground reaction force. Throughout the stance phase, EMG activity of shank muscles was typically found to increase whilst wearing the textured insoles.

DISCUSSION AND CONCLUSION

Despite some positive changes in gait patterns when wearing textured insoles, an increased foot-shank angle in terminal stance suggests that patients did not propel their swing limb through increased contribution of ankle plantarflexor muscles, perhaps favouring more proximal muscle groups. Whilst the textured insoles may alter gait patterns in MS patients, their contribution to achieving a more regular gait pattern with sufficient propulsion from ankle plantarflexors remains uncertain.

A novel approach to mechanical foot stimulation during human locomotion under body weight support

Input from the foot plays an essential part in perceiving support surfaces and determining kinematic events in human walking. To simulate adequate tactile pressure inputs under body weight support (BWS) conditions that represent an effective form of locomotion training, we here developed a new method of phasic mechanical foot stimulation using light-weight pneumatic insoles placed inside the shoes (under the heel and metatarsus). To test the system, we asked healthy participants to walk on a treadmill with different levels of BWS. The pressure under the stimulated areas of the feet and subjective sensations were higher at high levels of BWS and when applied to the ball and toes rather than heels. Foot stimulation did not disturb significantly the normal motor pattern, and in all participants we evoked a reliable step-synchronized triggering of stimuli for each leg separately. This approach has been performed in a general framework looking for "afferent templates" of human locomotion that could be used for functional sensory stimulation. The proposed technique can be used to imitate or partially restore surrogate contact forces under body weight support conditions.

Age-Related Differences in Stepping Response When Stepping onto a Known Soft Surface under Dual Task Conditions

The purpose of this study was to investigate whether age-related differences in stepping response influence postural control when stepping onto a known soft surface under dual task conditions. Nine young and eleven older female adults participated. First, they stepped on a flat surface while grasping an empty cup (single task), and then they repeated the task while grasping a cup filled with water (dual task). For the second experiment, they stepped on a soft surface placed in front of them while performing the above tasks. The main result was that %DIP (initiation phase as a percentage of the total stepping task time) was significantly higher for older than for young adults during the dual task on the soft surface. In conclusion, caution due to previous experience may increase attentional demand during dual tasks and lengthen the time required for central nervous processing in order to avoid losing postural stability in older adults, resulting in reductions in step velocity and step length compared to those in young adults.

Sensitivity mapping of the human foot: thresholds at 30 skin locations

BACKGROUND

Mechanoreceptors in the skin provide sensory input for the central nervous system about foot placement and loading. This information is used by the brain to actively control or regain balance and is important to establish memory traces for subsequent movement. A sensitivity map of the human foot could help to understand the mechanisms of the foot as a sensory organ for movement adjustment and balance control.

MATERIALS AND METHODS

Touch and vibration perception threshold values from 30 plantar and dorsal foot locations were determined in more than 40 women and men between 20 and 35 years. Semmes Weinstein monofilaments and a vibrotactile neurothesiometer were used for skin sensitivity threshold detection.

RESULTS

Large sensitivity differences were present between the 30 different foot sites. Gender effects were not present for touch but women had better sensitivities for vibration (p < 0.01), especially on the dorsal aspect of the foot. Age, in our cohort of 20- to 35-year-olds, did not have an influence on vibration or touch sensitivity. The heel had the highest detection thresholds for touch but was very sensitive for vibration stimuli. Compared to the dorsum, the plantar foot was substantially more sensitive, especially for vibration detection.

CONCLUSION

The results suggest that primarily the fast adapting plantar mechanoreceptors are important in assisting balance control during human locomotion.

CLINICAL RELEVANCE

The sensitivity map of the foot will help in understanding the function of the foot as a sensory organ and could be useful in creating footwear for better balance control and for the design of comfortable shoes.

Diabetic polyneuropathy may increase the handicap related to vestibular disease

BACKGROUND AND AIMS

We undertook this study to assess the influence of diabetic peripheral neuropathy on self-reported disability and postural control during quiet stance of patients with peripheral vestibular disease, before and after a standardized program of vestibular rehabilitation (Cawthorne & Cooksey exercises).

METHODS

Twenty patients with peripheral vestibular disease participated in the study (mean age 56+/-7.8 years), 10 with and 10 without peripheral neuropathy (age matched). The Dizziness Handicap Inventory and static posturography (eyes open/closed and firm/soft surface) were evaluated prior to rehabilitation and at week 7 of follow-up.

RESULTS

Compared to patients without neuropathy, patients with neuropathy had more time elapsed since the diabetes was diagnosed, higher glycemia and HbAc level and higher composite scores on the Dizziness Handicap Inventory, but similar results on static posturography. After rehabilitation, although scores on the Dizziness Handicap Inventory decreased in the two groups, the difference between them persisted. In patients with neuropathy, static posturography showed improvement of postural control only with the eyes closed and soft surface, whereas in patients without neuropathy the postural control improved during all sensory conditions (eyes open/closed and firm/soft surface).

CONCLUSIONS

In diabetic patients with peripheral vestibular disease, peripheral neuropathy contributes to self-reported disability and may interfere with complete balance recovery.

A model of postural control in quiet standing: robust compensation of delay-induced instability using intermittent activation of feedback control

The main purpose of this study is to compare two different feedback controllers for the stabilization of quiet standing in humans, taking into account that the intrinsic ankle stiffness is insufficient and that there is a large delay inducing instability in the feedback loop: 1) a standard linear, continuous-time PD controller and 2) an intermittent PD controller characterized by a switching function defined in the phase plane, with or without a dead zone around the nominal equilibrium state. The stability analysis of the first controller is carried out by using the standard tools of linear control systems, whereas the analysis of the intermittent controllers is based on the use of Poincaré maps defined in the phase plane. When the PD-control is off, the dynamics of the system is characterized by a saddle-like equilibrium, with a stable and an unstable manifold. The switching function of the intermittent controller is implemented in such a way that PD-control is 'off' when the state vector is near the stable manifold of the saddle and is 'on' otherwise. A theoretical analysis and a related simulation study show that the intermittent control model is much more robust than the standard model because the size of the region in the parameter space of the feedback control gains (P vs. D) that characterizes stable behavior is much larger in the latter case than in the former one. Moreover, the intermittent controller can use feedback parameters that are much smaller than the standard model. Typical sway patterns generated by the intermittent controller are the result of an alternation between slow motion along the stable manifold of the saddle, when the PD-control is off, and spiral motion away from the upright equilibrium determined by the activation of the PD-control with low feedback gains. Remarkably, overall dynamic stability can be achieved by combining in a smart way two unstable regimes: a saddle and an unstable spiral. The intermittent controller exploits the stabilizing effect of one part of the saddle, letting the system evolve by alone when it slides on or near the stable manifold; when the state vector enters the strongly unstable part of the saddle it switches on a mild feedback which is not supposed to impose a strict stable regime but rather to mitigate the impending fall. The presence of a dead zone in the intermittent controller does not alter the stability properties but improves the similarity with biological sway patterns. The two types of controllers are also compared in the frequency domain by considering the power spectral density (PSD) of the sway sequences generated by the models with additive noise. Different from the standard continuous model, whose PSD function is similar to an over-damped second order system without a resonance, the intermittent control model is capable to exhibit the two power law scaling regimes that are typical of physiological sway movements in humans.

The effect of reduced somatosensation on standing balance: a systematic review

The objective of this review is to identify and review publications describing the impact of reduced somatosensation on balance. Based on knowledge of the association between specific somatosensory loss and deterioration of balance, conclusions can be made about role of somatosensation in standing balance. A systematic literature review is presented in which publications from the years 1993 through 2007 were searched in Medline and Embase. Medical Subject Headings (MESH) terms and free text words (related to balance, somatosensory loss, and lower limb) were used to perform the searches. Fifteen articles were selected for detailed review based on predetermined inclusion criteria, and three of the included articles described the effect of experimentally reduced somatosensation on balance in healthy subjects. Ten of the articles described balance in diabetic neuropathy (DN). The last two included articles described balance in Charcot-Marie-Tooth (CMT) disease type 1A (CMT1A) or type 2 (CMT2). The literature indicates that the tactile sensation is reduced in DN, CMT1A, and CMT2 and when the plantar surface of the feet was hypothermically anesthetized. Joint motion sensation seems to be impaired in patients with DN, and passive joint position sensation appears to be reduced in healthy subjects with anesthesia of ankle and foot from prolonged ischemia. This reduced somatosensation seems to have a negative effect on balance in patients with DN and CMT2; however, this appeared not to be the case in patients with CMT1A and in healthy subjects.

Plantar cutaneous sensory stimulation improves single-limb support time, and EMG activation patterns among individuals with Parkinson's disease

Parkinson's disease is a chronic neurological disorder that results in gait and posture impairment. There is increasing evidence that these motor impairments may be partially due to deficits within the sensory system. In this study, the effects of a facilitatory insole that provides increased plantar sensory stimulation, was evaluated during gait, in a group of individuals with Parkinson's disease in comparison with healthy age-matched controls. Spatial-temporal parameters of gait were evaluated using an instrumented carpet, and muscle activation patterns were evaluated using surface EMG. All participants were tested with both a facilitatory (ribbed) insole and a conventional (flat) insole while walking 20 feet. Results indicated that the use of the facilitatory insole produced a significant increase in single-limb support time. Additionally, the muscle activation sequence of the tibialis anterior was normalized by the facilitatory insole, at the time of initial ground contact. These changes may lead to an overall improvement in gait pattern and stability, and suggest that the use of this type of facilitatory insole may be a useful treatment strategy for improving the gait of individuals with Parkinson's disease. This also provides support for the role of facilitation of the sensory system in improving motor output in individuals with Parkinson's disease.

Effect of reduced cutaneous cues on motion perception and postural control

To investigate whether the sensory perception could be a more direct assessment of sensory deficit as oppose to the postural performance, we examined the effect of reduced cutaneous cues on motion perception and motion control. The subject was translated in a mediolateral direction with a single sinusoidal acceleration at a stimulus frequency of 0.25 Hz with a peak acceleration magnitude ranging from 0.25 to 8 mG in the dark. Two different plantar cutaneous conditions were provided: the control condition (barefoot) and the reduced cutaneous condition (foot on a spongy surface). For each foot-sole sensory condition, the subject completed six sets of 33 randomly ordered translation stimuli. After each translational stimulus, the subject reported their perceived direction of motion by pressing a hand-held button. The center of pressure (COP) and joint kinematics of the quiet stance were also measured. The results showed a significant increase in perception threshold as well as COP variation in the anteroposterior direction in the reduced cutaneous cue trials. However, a non-significant increase in COP in the mediolateral direction was shown. Multivariate covariance analysis of joint kinematics showed changes in postural coordination, such as increased reliance on hip strategy under reduced cutaneous cues condition, that have not been differentiated by univariate measures. The observed discrepancy in the significance of the contribution of plantar cutaneous cues to the detection threshold and the COP variation implies that the 'perception' could provide more direct and sensitive assessment of the sensory degradation than the 'action'.

Effects of plantar hardness discrimination training on standing postural balance in the elderly: a randomized controlled trial

Objective: To investigate the effects of sensory perception exercises for discrimination of surface hardness by the soles of the feet on standing postural balance in the elderly.

Design: A randomized two-group parallel controlled trial.

Subjects: Twenty-four healthy people aged from 61 to 71 years were enrolled and randomly assigned to a perception exercise group (n = 12) or a control group (n = 12).

Intervention: The perception exercise group were given a task designed to train ability to discriminate different degrees of hardness of foam rubber. The training period was 10 days. Control group subjects were instructed to maintain a standing posture on foam rubber for 10 seconds for a total of 10 days.

Measurements: Before and after training we measured centre-of-gravity sway with the subject standing, obtaining sway path length and area of ellipse. The Functional Reach Test was used to measure the forward displacement distance of the centre of gravity.

Results: Our data revealed a significant reduction in centre-of-gravity sway post training in the perception exercise group as well as a significant increase in forward displacement of the centre of gravity. These parameters were unchanged in the control group. As to change values (difference between pre- and post-training values), the perception exercise group had significantly better values than the control group, indicating the efficacy of sensory perception exercises.

Conclusions: We demonstrated that standing postural balance was improved by sensory perception exercises involving the soles of the feet. Used in addition to balance training, such training for hardness discrimination could be effective in the clinical setting to improve balance in the elderly.

Frontal plane ankle proprioceptive thresholds and unipedal balance

Reliable unipedal balance is fundamental to safe ambulation. Accordingly, older persons with peripheral neuropathy (PN), who are at increased risk for falls, demonstrate impaired unipedal balance. To explore the relationship between afferent function and unipedal balance, frontal plane proprioceptive thresholds at the ankle were quantified in 22 subjects (72.5 +/- 6.3 years; 11 with PN and 11 matched controls) while they were standing using a foot cradle system and a staircase series of 100 rotational stimuli. PN subjects, as compared to controls, demonstrated shorter median unipedal balance times (3.4 +/- 2.7 vs. 14.3 +/- 8.9 s; P = 0.0017) and greater (less precise) combined ankle inversion/eversion proprioceptive thresholds (1.17 +/- 0.36 vs. 0.65 +/- 0.37 degrees ; P = 0.0055). Combined ankle inversion/eversion proprioceptive thresholds explained approximately half the variance in unipedal balance time (R2 = 0.5138; P = 0.0004). Given prior work demonstrating a similarly strong relationship between ankle torque generation and unipedal balance, neuropathy-associated impairments in ankle frontal plane afferent and efferent function appear to be equally responsible for the inability of older persons with PN to reliably balance on one foot. They therefore provide distinct targets for intervention.

Electromyographic responses from the hindlimb muscles of the decerebrate cat to horizontal support surface perturbations

The sensory and neural mechanisms underlying postural control have received much attention in recent decades but remain poorly understood. Our objectives were 1) to establish the decerebrate cat as an appropriate model for further research into the sensory mechanisms of postural control and 2) to observe what elements of the postural response can be generated by the brain stem and spinal cord. Ten animals were decerebrated using a modified premammillary technique, which consists of a premammillary decerebration that is modified with a vertical transection near the subthalamic nucleus to eliminate spontaneous locomotion. Horizontal support surface perturbations were applied to all four limbs and electromyographic recordings were collected from 14 muscles of the right hindlimb. Muscle activation was quantified with tuning curves, which compared increases and decreases in muscle activity to background and graphed the difference against perturbation direction. Parallels were drawn between these tuning curves, which were further quantified with a principal direction and breadth (range of directions of muscle activation), and data collected by other researchers from the intact animal. We found a strong similarity in the direction and breadth of the tuning curves generated in the decerebrate and intact cat. These results support our hypothesis that directionally specific tuning of muscles in response to support surface perturbations does not require the cortex, further indicating a strong role for the brain stem and spinal cord circuits in mediating directionally appropriate muscle activation patterns.

Plantar pressure distribution in gait is not affected by targeted reduced plantar cutaneous sensation

BACKGROUND

Plantar ulcers are a common and severe complication of the diabetic neuropathic foot. Increased plantar pressures while walking are associated to incidence of plantar ulcer formation in diabetes. There is a strong correlation between the increase in plantar pressures and the severity of peripheral neuropathy. One consequence of peripheral sensory neuropathy is insensitive skin. The influence of reduced plantar sensitivity on changes in plantar pressure distribution is not well understood. The purpose of this study was to identify possible causal dependences between reduced plantar cutaneous sensation and plantar pressure distribution during gait.

METHODS

Dynamic pressure distribution in gait and sensory perception threshold for pressure touch and vibration (25Hz/200Hz) of the plantar foot were determined pre and post sensory intervention in ten healthy subjects. Cutaneous sensation in both foot soles was experimentally reduced by means of intradermal injections of an anaesthetic solution. This procedure leaves foot and ankle proprioception as well as intrinsic foot muscles unaffected.

FINDINGS

The intervention significantly reduced plantar cutaneous sensation to the level of sensory neuropathy. Plantar pressure and force variables, contact times for the entire foot and for the plantar foot regions were not influenced significantly.

INTERPRETATION

Experimentally reducing plantar cutaneous sensation causes no changes in plantar pressure distribution while walking. Our findings suggest that in the diabetic neuropathic foot insensitive plantar skin due to peripheral sensory neuropathy may be not a decisive factor for altering plantar pressures. This is underpinning the importance of concomitant affection of different systems secondary to diabetic peripheral neuropathy.

Potential roles of force cues in human stance control

Human stance is inherently unstable. A small deviation from upright body orientation is enough to yield a gravitational component in the ankle joint torque, which tends to accelerate the body further away from upright ('gravitational torque'; magnitude is related to body-space lean angle). Therefore, to maintain a given body lean position, a corresponding compensatory torque must be generated. It is well known that subjects use kinematic sensory information on body-space lean from the vestibular system for this purpose. Less is known about kinetic cues from force/torque receptors. Previous work indicated that they are involved in compensating external contact forces such as a pull or push having impact on the body. In this study, we hypothesized that they play, in addition, a role when the vestibular estimate of the gravitational torque becomes erroneous. Reasons may be sudden changes in body mass, for instance by a load, or an impairment of the vestibular system. To test this hypothesis, we mimicked load effects on the gravitational torque in normal subjects and in patients with chronic bilateral vestibular loss (VL) with eyes closed. We added/subtracted extra torque to the gravitational torque by applying an external contact force (via cable winches and a body harness). The extra torque was referenced to body-space lean, using different proportionality factors. We investigated how it affected body-space lean responses that we evoked using sinusoidal tilts of the support surface (motion platform) with different amplitudes and frequencies (normals +/-1 degrees, +/-2 degrees, and +/-4 degrees at 0.05, 0.1, 0.2, and 0.4 Hz; patients +/-1 degrees and +/-2 degrees at 0.05 and 0.1 Hz). We found that added/subtracted extra torque scales the lean response in a systematic way, leading to increase/decrease in lean excursion. Expressing the responses in terms of gain and phase curves, we compared the experimental findings to predictions obtained from a recently published sensory feedback model. For the trials in which the extra torque tended to endanger stance control, predictions in normals were better when the model included force cues than without these cues. This supports our notion that force cues provide an automatic 'gravitational load compensation' upon changes in body mass in normals. The findings in the patients support our notion that the presumed force cue mechanism provides furthermore vestibular loss compensation. Patients showed a body-space stabilization that cannot be explained by ankle angle proprioception, but must involve graviception, most likely by force cues. Our findings suggest that force cues contribute considerably to the redundancy and robustness of the human stance control system.

Can tactile plantar stimulation improve postural control of persons with superficial plantar sensory deficit?

BACKGROUND AND AIMS

Complex interactions between visual, vestibular and somatosensory information and the cerebellar system are involved in the maintenance of upright posture. Previous studies have shown that normal aging and pathologies may lead to deterioration of the control of upright standing posture.

METHODS

In order to investigate postural control during quiet standing in the elderly, the center of pressure (CoP) was analysed on two force platforms in three different groups. The first group was composed of 13 healthy older adults (O), the second consisted of 9 older adults with plantar sole deficit (OD), and the third (control) group was composed of 8 young healthy subjects (Y). All subjects were tested with eyes closed, before and after tactile plantar stimulation lasting ten minutes. Center of pressure displacements were analyzed in terms of sway area, mean velocity, and mean root mean square (RMS) along both mediolateral and antero-posterior axes.

RESULTS

Results showed that, before tactile plantar stimulation, the sway area and mean RMS were greater in O and OD subjects compared with Y ones. After tactile plantar stimulation, a decrease in the mean RMS was observed in OD subjects, this effect being significant only for the medio-lateral axis.

CONCLUSIONS

These results suggest that application of tactile plantar stimulation may compensate a loss of superficial plantar sensitivity.

Foot and ankle compression improves joint position sense but not bipedal stance in older people

This study investigates the effects of foot and ankle compression on joint position sense (JPS) and balance in older people and young adults. 12 independently living healthy older persons (77-93 years) were recruited from a senior accommodation facility. 15 young adults (19-24 years) also participated. Compression was applied at the ankles and feet using medical compression hosiery. The mean velocity of the centre of pressure (CoP) displacements and the root mean square of the CoP velocity in both anteroposterior and mediolateral directions, were measured with a foot pressure plate. In older people, ankle compression was associated with an improvement of JPS towards normal values. However, a concurrent deterioration of their balance was found. In young adults compression had no effect on either JPS or balance.

Effects of external loads on balance control during upright stance: experimental results and model-based predictions

The purpose of this study was to identify the effects of external loads on balance control during upright stance, and to examine the ability of a new balance control model to predict these effects. External loads were applied to 12 young, healthy participants, and effects on balance control were characterized by center-of-pressure (COP) based measures. Several loading conditions were studied, involving combinations of load mass (10% and 20% of individual body mass) and height (at or 15% of stature above the whole-body COM). A balance control model based on an optimal control strategy was used to predict COP time series. It was assumed that a given individual would adopt the same neural optimal control mechanisms, identified in a no-load condition, under diverse external loading conditions. With the application of external loads, COP mean velocity in the anterior-posterior direction and RMS distance in the medial-lateral direction increased 8.1% and 10.4%, respectively. Predicted COP mean velocity and RMS distance in the anterior-posterior direction also increased with external loading, by 11.1% and 2.9%, respectively. Both experimental COP data and model-based predictions provided the same general conclusion, that application of larger external loads and loads more superior to the whole body center of mass lead to less effective postural control and perhaps a greater risk of loss of balance or falls. Thus, it can be concluded that the assumption about consistency in control mechanisms was partially supported, and it is the mechanical changes induced by external loads that primarily affect balance control.

Post-effect of forward and backward locomotion on body orientation in space during quiet stance

Neural circuits responsible for stance control serve other motor tasks as well. We investigated the effect of prior locomotor tasks on stance, hypothesizing that postural post-effects of walking are dependent on walking direction. Subjects walked forward (WF) and backward (WB) on a treadmill. Prior to and after walking they maintained quiet stance. Ground reaction forces and centre of foot pressure (CoP), ankle and hip angles, and trunk inclination were measured during locomotion and stance. In WF compared to WB, joint angle changes were reversed, trunk was more flexed, and movement of CoP along the foot sole during the support phase of walking was opposite. During subsequent standing tasks, WB induced ankle extension, hip flexion, trunk backward leaning; WF induced ankle flexion and hip extension. The body CoP was displaced backward post-WB and forward post-WF. The post-effects are walking-direction dependent, and possibly related to foot-sole stimulation pattern and trunk inclination during walking.

The effect of immersion cryotherapy on medial-lateral postural sway variability in individuals with a lateral ankle sprain

BACKGROUND AND PURPOSE

Postural stability has been shown to be impaired after a lateral ankle sprain (LAS) and after immersion cryotherapy in healthy ankles. This study was performed to determine the effects of cryotherapy on postural stability after LAS.

METHOD

A single-session, repeated measures design was used. Fifteen 18- to 29-year-old males (mean age 21.33 +/- 3.54, height 71.23 +/- 2.50 cm, mass 170.33 +/- 19.77 kg) with relatively recent grade I LAS volunteered. Medial-lateral postural sway variability was assessed during single-leg barefoot stance using a Bertec force platform. Sway was tested before cryotherapy ('Pre'), immediately after 20 minutes of lower-leg immersion cryotherapy ('Post(0)'), and 10 and 20 minutes after cryotherapy ('Post(10)' and 'Post(20)'). Both legs were tested (individually) before cryotherapy; the involved leg was tested alone after cryotherapy. The uninvolved leg served as a control.

RESULTS

Postural sway variability of the involved le was significantly greater than the uninvolved le before cryotherapy (p = 0.001). Postural sway variability of the involved leg was also significantly greater than the uninvolved LE during Post(0) (p = 0.000), Post(10) (p = 0.000) and Post(20) testing (p = 0.003) with the largest increase in sway variability occurring at Post(0).

CONCLUSIONS

Medial-lateral postural sway variability was greater after LAS. This effect was augmented by immersion cryotherapy.

Identifying deficits in balance control following vestibular or proprioceptive loss using posturographic analysis of stance tasks

OBJECTIVE

To distinguish between normal and deficient balance control due to vestibular loss (VL) or proprioceptive loss (PL) using pelvis and shoulder sway measures.

METHODS

Body-worn gyroscopes measured pelvis and shoulder sway in pitch (anterior-posterior) and roll (side-to-side) directions in 6 VL, 6 PL and 26 control subjects during 4 stance tasks. Sway amplitudes were compared between groups, and were used to select optimal measures that could distinguish between these groups.

RESULTS

VL and PL patients had greater sway amplitudes than controls when standing on foam with eyes closed. PL patients also swayed more when standing with eyes closed on firm support and eyes open on foam. Standard sensory analysis techniques only differentiated VL patients from controls. Stepwise discriminate analysis showed that differentiation required pitch measures for VL patients, roll measures for PL patients, and both measures for all three groups. Pelvis measures yielded better discrimination than shoulder measures.

CONCLUSIONS

Distinguishing between normal and deficient balance control due to VL or PL required pitch and roll pelvis sway measures.

SIGNIFICANCE

Accurate identification of balance deficits due to VL or PL may be useful in clinical practice as a functional diagnostic tool or to monitor balance improvements in VL or PL patients.

Sensitivity of plantar cutaneous sensation and postural stability

BACKGROUND

Impaired plantar cutaneous sensation is often seen clinically and can lead to postural instability. It is not clear if the severity of such sensory loss would be associated with postural stability, and if such an association would be affected by sensory redundancy and task difficulty. The purpose of this study was to investigate the association of the degree of somatosensory loss and postural stability by experimentally induced somatosensory loss in healthy young adults.

METHODS

Twenty-one healthy young adults performed four quiet standing tasks (normal or narrow base, and eyes open or closed) on a force platform under three somatosensory conditions induced by ischemic blocking of afferent conduction below the ankle, normal, partial loss and complete loss. Differences in the standing center of pressure motion between the three sensory loss conditions were compared.

FINDINGS

There was a significant trend of greater center of pressure motion with increasing severity of sensory loss in all task conditions. The differences in the center of pressure motion between partial and total loss conditions were significant only in conditions where vision was removed and the support surface was narrow.

INTERPRETATION

Increased severity of experimentally induced loss of plantar cutaneous sensitivity was associated with greater postural sway. Such an association was affected by the availability of visual input and the size of the support surface. Clinically for patients with somatosensory impairments of the foot, postural stability should be given special attention.

Do spike insoles enhance postural stability and plantar-surface cutaneous sensitivity in the elderly?

Balance problems are often related to a loss of plantar-sensitivity in elderly people. The purpose of this study was to explore the contribution of plantar cutaneous inputs induced by a spike support surface to the control of stance. Nineteen elderly (mean age 69.0 years, range 62-80) and 19 young adults (mean age 25.9 years, range 21-32) were instructed to stand (standing session) or to walk (walking session) for 5 min with sandals equipped with spike insoles (spike condition). Both sessions also involved a no spike condition in which participants stood or walked for 5 min without these insoles (no spike condition). In all conditions, postural responses were assessed during unperturbed stance and were performed (1) immediately after putting the spike or the no spike insoles, and (2) 5 min after standing or walking with them. Sway parameters, such as centre of foot pressure mean location, surface area, mean speed, root mean square and median frequency on the antero-posterior and medio-lateral axes, were calculated. As postural performances are often related to plantar-surface sensitivity, cutaneous sensitivity threshold was also evaluated with Semmes-Weinstein monofilaments. Although no immediate effect of the spike insoles was found, results indicated that standing or walking for 5 min with sandals equipped with spike insoles led to a significant improvement of quiet standing in the elderly. Balance improvement was also observed in young adults. The results provided evidence that wearing sandals with spike insoles can contribute, at least temporarily, to the improvement of unperturbed stance in elderly people with relatively intact plantar cutaneous sensation. Further research is needed to assess the effects of longer and discontinuous stimulations with spike insoles on postural control.

Biomechanics of Tai Chi: a review

Tai Chi Chuan is a favourite form of exercise throughout the world and has drawn increasing research interest from international scientists. Biomechanical research into Tai Chi has grown substantially and has provided evidence of the beneficial effects of Tai Chi exercise on health, fitness, and prevention of falls. This paper reviews studies that have explored the biomechanical aspects of Tai Chi, such as balance, kinematics, kinetics, strength, and neuromuscular activities.

Sensory supplementation system based on electrotactile tongue biofeedback of head position for balance control

The present study aimed at investigating the effects of an artificial head position-based tongue-placed electrotactile biofeedback on postural control during quiet standing under different somatosensory conditions from the support surface. Eight young healthy adults were asked to stand as immobile as possible with their eyes closed on two Firm and Foam support surface conditions executed in two conditions of No-biofeedback and Biofeedback. In the Foam condition, a 6-cm thick foam support surface was placed under the subjects' feet to alter the quality and/or quantity of somatosensory information at the plantar sole and the ankle. The underlying principle of the biofeedback consisted of providing supplementary information about the head orientation with respect to gravitational vertical through electrical stimulation of the tongue. Centre of foot pressure (CoP) displacements were recorded using a force platform. Larger CoP displacements were observed in the Foam than Firm conditions in the two conditions of No-biofeedback and Biofeedback. Interestingly, this destabilizing effect was less accentuated in the Biofeedback than No-biofeedback condition. In accordance with the sensory re-weighting hypothesis for balance control, the present findings evidence that the availability of the central nervous system to integrate an artificial head orientation information delivered through electrical stimulation of the tongue to limit the postural perturbation induced by alteration of somatosensory input from the support surface.

Effects of changing the initial horizontal location of the center of mass on the anticipatory postural adjustments and task performance associated with step initiation

The aim of this study was to elucidate whether and how the duration and/or amplitude parameters of anticipatory postural adjustments (APAs) affected the task performance in a single step forward from differences in the initial horizontal location of CoM. Ten male subjects performed initiation of a single step forward with the right swing leg with strict regulation of the step length at three initial body positions (Sw, step initiation from a 50% position of the center of pressure (CoP) shift in the maximum lateral right side; N, step initiation from the upright position at rest; St, step initiation from a 50% position of the CoP shift in the maximum lateral left side). The duration required for stepping from the heel-off to foot-contact of the swing leg (step time) in the Sw condition was significantly shorter than of the other two conditions. The APAs durations in the Sw condition was significantly longer than in the other two conditions. In the Sw condition, the durations of the anticipatory electromyographic (EMG) activities of the tibialis anteriors (TA) of the swing leg correlated significantly with mechanical parameters (the displacement of the CoM, velocity of the CoM, and propulsive force) in the anticipatory phase, while the mean amplitudes of the anticipatory EMG activities of the TA of the swing leg did not correlate significantly with mechanical parameters in the anticipatory phase. The present results suggest that the duration parameters of the APAs associated with single step forward motion are dependent on the displacement of the CoM estimated by the initial cutaneous messages from the swing leg prior to initiation of the single step, and that the APAs may be directly involved not only in the increase in propulsive force towards the supporting leg, but also increasing the forward propulsive force at heel-off.

The load/capacity ratio affects the sit-to-stand movement strategy

BACKGROUND

In this study the effect of a changed load/capacity ratio on sit-to-stand performance and on the underlying net joint moments was investigated. In subjects with muscle weakness the load/capacity ratio is increased due to reduced muscle capacity. In the current study this ratio was manipulated by changing the load. This approach allowed studying the isolated effect of an increased load/capacity ratio on sit-to-stand strategy.

METHODS

Ten healthy women performed sit-to-stand movements under four load conditions. The load/capacity ratio was manipulated by adding 0%, 15%, 30% and 45% of the body mass to a weight vest. To determine changes in sit-to-stand strategy flexion of the trunk and temporal characteristics were assessed. Joint moments at ankle, knee and hip joints and activation patterns of major leg muscles were determined from the kinematics and kinetics.

FINDINGS

Increasing the extra load from 30% to 45% changed the sit-to-stand performance. In the 45% condition maximal trunk flexion was increased and movement time significantly elongated. The strategy change was associated with a disproportionate increase of the net hip extension moment and a delayed peak of the net knee extension moment.

INTERPRETATION

This study shows that experimentally observed changes in sit-to-stand strategy can be attributed to an increase in the load/capacity ratio. For treatment purposes this implies that increasing muscle strength, reducing body mass or a combination of these could be a suitable approach to improve sit-to-stand performance. The experimental model applied will be useful to study the isolated effect of the load/capacity ratio.

Re-weighting of somatosensory inputs from the foot and the ankle for controlling posture during quiet standing following trunk extensor muscles fatigue

The present study focused on the effects of trunk extensor muscles fatigue on postural control during quiet standing under different somatosensory conditions from the foot and the ankle. With this aim, 20 young healthy adults were asked to stand as immobile as possible in two conditions of No fatigue and Fatigue of trunk extensor muscles. In Experiment 1 (n = 10), somatosensation from the foot and the ankle was degraded by standing on a foam surface. In Experiment 2 (n = 10), somatosensation from the foot and ankle was facilitated through the increased cutaneous feedback at the foot and ankle provided by strips of athletic tape applied across both ankle joints. The centre of foot pressure displacements (CoP) were recorded using a force platform. The results showed that (1) trunk extensor muscles fatigue increased CoP displacements under normal somatosensatory conditions (Experiment 1 and Experiment 2), (2) this destabilizing effect was exacerbated when somatosensation from the foot and the ankle was degraded (Experiment 1), and (3) this destabilizing effect was mitigated when somatosensation from the foot and the ankle was facilitated (Experiment 2). Altogether, the present findings evidenced re-weighting of sensory cues for controlling posture during quiet standing following trunk extensor muscles fatigue by increasing the reliance on the somatosensory inputs from the foot and the ankle. This could have implications in clinical and rehabilitative areas.

A rehabilitation tool for functional balance using altered gravity and virtual reality

Background

There is a need for effective and early functional rehabilitation of patients with gait and balance problems including those with spinal cord injury, neurological diseases and recovering from hip fractures, a common consequence of falls especially in the elderly population. Gait training in these patients using partial body weight support (BWS) on a treadmill, a technique that involves unloading the subject through a harness, improves walking better than training with full weight bearing. One problem with this technique not commonly acknowledged is that the harness provides external support that essentially eliminates associated postural adjustments (APAs) required for independent gait. We have developed a device to address this issue and conducted a training study for proof of concept of efficacy.

Methods

We present a tool that can enhance the concept of BWS training by allowing natural APAs to occur mediolaterally. While in a supine position in a 90 deg tilted environment built around a modified hospital bed, subjects wear a backpack frame that is freely moving on air-bearings (cf. puck on an air hockey table) and attached through a cable to a pneumatic cylinder that provides a load that can be set to emulate various G-like loads. Veridical visual input is provided through two 3-D automultiscopic displays that allow glasses free 3-D vision representing a virtual surrounding environment that may be acquired from sites chosen by the patient. Two groups of 12 healthy subjects were exposed to either strength training alone or a combination of strength and balance training in such a tilted environment over a period of four weeks.

Results

Isokinetic strength measured during upright squat extension improved similarly in both groups. Measures of balance assessed in upright showed statistically significant improvements only when balance was part of the training in the tilted environment. Postural measures indicated less reliance on visual and/or increased use of somatosensory cues after training.

Conclusion

Upright balance function can be improved following balance specific training performed in a supine position in an environment providing the perception of an upright position with respect to gravity. Future studies will implement this concept in patients.

Body weight is a strong predictor of postural stability

Proper balance control is a key aspect of acitivities of daily living. The aim of this study was to determine the contribution of body weight to predict balance stability. The balance stability of 59 male subjects with BMI ranging from 17.4 to 63.8kg/m(2) was assessed using a force platform. The subjects were tested with and without vision. A stepwise multiple regression analysis was used to determine the independent effect of body weight, age, body height and foot length on balance stability (i.e., mean speed of the center of foot pressure). With vision, the stepwise multiple regression revealed that body weight accounted for 52% of the variance of balance stability. The addition of age contributed a further 3% to explain balance control. Without vision, body weight accounted for 54% of the variance and the addition of age and body height added a further 8% and 1% to explain the total variance, respectively. The final model explained 63% of the variance. A decrease in balance stability is strongly correlated to an increase in body weight. This suggests that body weight may be an important risk factor for falling. Future studies should examine more closely the combined effect of aging and obesity on falling and injuries and the impact of obesity on the diverse range of activities of daily living.

Diminished plantar cutaneous sensation and postural control

The purpose of this study was to assess the effect of diminished plantar cutaneous sensation induced by cooling on postural control during double- and single-limb quiet standing. 32 healthy adults were tested on an intervention day and control day. The intervention consisted of 10 min. of ice immersion of the plantar aspect of the feet prior to balance testing. Dependent variables were center of pressure velocity and area during double- and single-limb stance with eyes open and closed. Significant interactions were found between sensation and vision for double-limb center of pressure area, with a significant reduction in area of center of pressure excursions after reducing sensation with eyes closed but not with eyes open. The area of center of pressure excursions may have been reduced in an effort to curtail exploratory postural behavior given the altered afferent input from plantar receptors. There were no significant differences for plantar hypoesthesia in single-limb stance.

Reliability of voluntary step execution behavior under single and dual task conditions

Background

The current study investigated the repeatability (test-retest reliability) of ground reaction force parameters recorded during a voluntary step execution under single (motor task) and dual task (motor and cognitive task) conditions for healthy adults and elderly individuals as well as the number of trials required to produce repeatable results.

Methods

Twenty-four healthy adults (21–63 years old) and 16 elderly adults (66–87 years) performed a voluntary rapid step execution following a tap on their heel while standing on a force platform under single and dual task conditions on three separate occasions. The first two tests were performed 30–60 minutes apart and the third test was performed a week later. Variables analyzed from the ground reaction force data included onset latency of step initiation (initiation phase), preparation and swing phases, foot-off and foot-contact times.

Results

Intraclass correlation coefficients (ICC(2,1)) were good to excellent across all parameters and test conditions for the pooled population and for elderly (0.74–0.92 and 0.62–0.88, respectively) except for the swing phase duration where lower values were seen (0.54–0.60 and 0.32–0.64 respectively). Values were similar under single and dual task conditions.

Conclusion

A voluntary step execution test, performed under single and dual task conditions especially foot-off and foot-contact times, is a reliable outcome measure that may be a useful tool to asses dynamic balance function for diagnostic purposes as well as clinical intervention trials.

Control of upright stance over inclined surfaces

The present work investigated the control of upright posture on inclined surfaces (14 degrees). Such conditions could, for example, change the contributions of muscle spindles resulting in alterations in postural sway. Subjects stood in quiet stance over a force platform positioned in one of three different fixed positions: horizontal (H), toes-up (ankle dorsi-flexion, D) and toes-down (ankle plantar-flexion, P). The experiments were done in the presence and also in the absence of vision. The analysis of the resulting sway was based on the power spectrum of the center of pressure displacement in the anterior-posterior direction (CP_ap). Analysis of the electromyogram (EMG) of the leg muscles and evaluation of the level of presynaptic inhibition (PSI) of the soleus (SO) Ia afferents complemented the study. The results showed that the spectrum of the CP_ap changed with the inclination of the surface of support. In condition D a higher instability was found as reflected by the higher spectral amplitudes at lower frequencies (below 0.3 Hz). On the other hand, the CP_ap of subjects in condition P contained increased amplitudes at high frequencies (above 0.3 Hz) and smaller amplitudes at low frequencies. The modifications found in the CP_ap power spectra when standing over an inclined surface may indicate changes in both short-term and long-term systems of postural control. These results do not seem to be associated with changes in group Ia feedback gain since no changes in the level of PSI were found among the three standing conditions. The SO EMG increased in condition P but did not change in condition D. On the other hand, the tibialis anterior had a tendency towards increased bursting activity in condition D. Eye closure caused an increase in the power of the oscillations at all spectral frequencies in the three standing conditions (H, P or D) and also a change in the profile of the CP_ap power spectrum. This may suggest a nonlinearity in the postural control system. The control of the slow component of the postural sway was more dependent on vision when the subject was in condition D, probably in association with the biomechanical constraints of standing on a toes-up ramp. A conclusion of this work was that, depending on the postural demand (direction of the ramp of support), the ensuing proprioceptive and biomechanical changes affect differentially the fast and slow mechanisms of balance control.

A systematic review of the effects of shoes and other ankle or foot appliances on balance in older people and people with peripheral nervous system disorders

The objective of this paper is to identify and review all publications on effects ankle and/or foot appliances (AFA) on balance in older people (>or=60 years) and patients with peripheral nervous system disorders (PNSD). These two groups account for the majority of the population with deteriorated balance due to peripheral somatosensory feedback problems. To provide a context for understanding and interpreting the studies that have been published to date, we will briefly summarize current theories on the role of somatosensory mechanisms in control of balance and how balance can be affected by AFA. A systematic literature review is presented in which publications were searched in Medline, Embase and Recal. In total 146 papers were identified and 18 were selected based on title and abstract for qualitative assessment by two independent reviewers. Based on assessment of the total articles, seven of the 18 papers fulfilled predetermined qualitative criteria and were selected for detailed review. No definitive conclusions can be drawn concerning the effects of AFA on balance in older people or in patients with PNSD because of the small number of studies and the weak level of evidence. The available literature seems to indicate that a training program may be helpful in ensuring the effectiveness of an appliance. Insoles with tubing or vibrating elements may improve balance, whereas thick or soft soles may deteriorate balance. The effects of these different types of insoles or soles are consistent with theories about somatosensory mechanisms that play a role in control of balance. More and better quality research is needed to support the prevalent use of appliances in these populations.

Analysis of Center-of-Pressure Data during Unipedal and Bipedal Standing Using Fractional Brownian Motion Modeling

To question the relation between uni- and bipedal postural skills, 21 subjects were required to stand on a force platform through uni- and bipedal conditions. These two protocols are commonly used paradigms to assess the balance capacities of healthy and disabled patients. The recorded displacements of the center of pressure (CP) were decomposed along mediolateral and anteroposterior axes and assessed through variance positions and parameters obtained from fractional Brownian motion (fBm) modeling to determine the nature and the spatiotemporal organization of the successive controlling mechanisms. The variances underline the relative independence of the two tasks. Nevertheless, as highlighted by the fBm framework, postural correction is initiated for the unipedal stance after shorter time delays and longer covered distances. When compared to bipedal standing, one of the main characteristics of unipedal standing is to induce better-controlled CP trajectories, as deduced from the scaling regimes computed from the fBm modeling. Lastly, the control of the CP trajectories during the shortest time intervals along the anteroposterior axis appears identical for both uni- and bipedal conditions. Unipedal and bipedal standing controls should thus be viewed as two complementary tasks, each providing specific and complementary insights into the postural control organization.

Plantar cutaneous input modulates differently spinal reflexes in subjects with intact and injured spinal cord

STUDY DESIGN

Spinal reflex excitability study in sensory-motor incomplete spinal cord-injured (SCI) and spinal intact subjects.

OBJECTIVES

To investigate the effects of plantar cutaneous afferent excitation on the soleus H-reflex and flexion reflex in both subject groups while seated.

SETTING

Rehabilitation Institute of Chicago and City University of New York, USA.

METHODS

The flexion reflex in SCI subjects was elicited by non-nociceptive stimulation of the sural nerve. In normal subjects, it was also elicited via innocuous medial arch foot stimulation. In both cases, reflex responses were recorded from the ipsilateral tibialis anterior muscle. Soleus H-reflexes were elicited and recorded via conventional methods. Both reflexes were conditioned by plantar cutaneous afferent stimulation at conditioning test intervals ranging from 3 to 90 ms.

RESULTS

Excitation of plantar cutaneous afferents resulted in facilitation of the soleus H-reflex and late flexion reflex in SCI subjects. In normal subjects, the soleus H-reflex was depressed while the late flexion reflex was absent. The early flexion reflex was irregularly observed in SCI patients, while in normal subjects a bimodal reflex modulation pattern was observed.

CONCLUSION

The effects of plantar cutaneous afferents change following a lesion to the spinal cord leading to exaggerated activity in both flexors and extensors. This suggests impaired modulation of the spinal inhibitory mechanisms involved in the reflex modulation. Our findings should be considered in programs aimed to restore sensorimotor function and promote recovery in these patients.

SPONSORSHIP

NIH, NICHD, Grant no. 1R03 HD 043951-01 and PSC CUNY Research Award no. 67051-0036.