An upper-body can improve the stability and efficiency of passive dynamic walking

The compass-gait walker proposed by McGeer can walk down a shallow slope with a self-stabilizing gait that requires no actuation or control. However, as the slope goes to zero so does the walking speed, and dynamic gait stability is only possible over a very narrow range of slopes. Gomes and Ruina have results demonstrating that by adding a torso to the compass-gait walker, it can walk passively on level-ground with a non-infinitesimal constant average speed. However, the gait involves exaggerated joint movements, and for energetic reasons horizontal passive dynamic walking cannot be stable. We show in this research that in addition to collision-free walking, adding a torso improves stability and walking speed when walking downhill. Furthermore, adding arms to the torso results in a collision-free periodic gait with natural-looking torso and limb movements. Overall, in contrast to the suggestions that active control may be needed to balance an upper-body on legs, it turns out that the upper and lower bodies can be integrated to improve the stability, efficiency and speed of a passive dynamic walker.     

The influence of gender and somatotype on single-leg upright standing postural stability in children

The purpose of this study was to investigate the influence of gender and somatotypes on single-leg upright standing postural stability in children. A total of 709 healthy children from different schools were recruited to measure the anthropometric somatotypes and the mean radius of center of pressure (COP) on a force platform with their eyes open and eyes closed. The results were that (a) girls revealed significantly smaller mean radius of COP distribution than boys, both in the eyes open and eyes closed conditions, and (b) the mesomorphic, muscular children had significantly smaller mean radius of COP distribution than the endomorphic, fatty children and the ectomorphic, linear children during the eyes closed condition. The explanation for gender differences might be due to the larger body weight in boys. The explanation for somatotype differences might be due to the significantly lower body height and higher portion of muscular profile in the mesomorphic children.     

The influence of geographic variations on the muscular activity in selected sports movements

Surface EMG (SEMG) has been used frequently to study motion techniques or skills, body positions, material or equipment used, training-methodology and learning processes in sports and ergonomics. Little if any information is available on the effect of the geographical environment on the neuromuscular control of an athlete or workman during his/her performance or effort.

Motions were chosen in Alpine skiing and cycling.

Thirty-one certified ski instructors and twelve professional road cyclists participated in the study of geographical variance and its impact on muscle activity.

SEMG was measured from the agonists and antagonists of the upper- and lower limb. Skiers were measured on downhill slopes ranging from 19 to 51% while the cyclists performed with different saddle positions on 2, 7 and 12% slope inclinations, respectively.

Verification of the variation of muscular intensity (IEMG) over the slope inclination during a simulated giant slalom indicated that the muscular activity increased with increasing slope angle and decreased with decreasing slope angle, while heart rate measured with short-range radio telemetry increased at a constant rate between start and finish independent of the geographical variations.

In a direct descent on different slopes % levels the integrated EMG is well related to the inclination (r=0.82) confirming the findings of the giant slalom.

In cycling we found that, regardless of the pelvis position, the muscular intensity of lower limb muscles increased with increasing slope inclination, while the muscular intensity of the arms decreased with the same increasing slope inclination. In addition the decreased intensity of the arm muscles remained significantly higher with the pelvis (saddle) fully forward.

The geography of the terrain did influence the neuromuscular work and therewith probably the performance also. The influence however, varies with specific circumstances and is coupled with items of variability of the equipment used and the body regions involved.     

Effect of dentures wearing on motor reaction time and balance function in elderly people

OBJECTIVE: To investigate the influence of dentures wearing on the parameters of physical fitness, particularly on agility and balance function in elderly people. DESIGN: A case control study.Setting: Motohachiohjimachi, Hachiohji, Tokyo, Japan. METHODS: Motor reaction time was measured in the presence and absence of dentures in the subjects who were 1) in a sitting position and lifted the lower limbs as fast as possible in response to a stimulus (Sitting Group) and those who were 2) in a standing position and jumped upright as fast as possible in response to a light stimulus (Jumping Group). The effects of dentures wearing on balance function were investigated by comparing the measured values of static and dynamic body sway. RESULTS AND CONCLUSIONS: Light-reaction time was not significantly influenced by dentures wearing in Sitting Group performing a light body movement that required little muscular force.In a relatively heavy body movement that required agility (i.e., jumping from the standing position), the reactivity changed depending on the muscular force; which might result in the difference of the reactivity due to dentures wearing (i.e., t-test showed a significant difference in the light-reaction time under clenching posture between with and without wearing dentures (p < 0.01)).No significant difference was observed in body sway under clenching posture between with and without wearing dentures.Therefore, we assumed that reaction speed varied depending upon dentures wearing.     

Nonexercise movement in elderly compared with young people

The association between free-living daily activity and aging is unclear because nonexercise movement and its energetic equivalent, nonexercise activity thermogenesis, have not been exhaustively studied in the elderly. We wanted to address the hypothesis that free-living nonexercise movement is lower in older individuals compared with younger controls matched for lean body mass. Ten lean, healthy, sedentary elderly and 10 young subjects matched for lean body mass underwent measurements of nonexercise movement and body posture over 10 days using sensitive, validated technology. In addition, energy expenditure was assessed using doubly labeled water and indirect calorimetry. Total nonexercise movement (acceleration arbitrary units), standing time, and standing acceleration were significantly lower in the elderly subjects; this was specifically because the elderly walked less distance per day despite having a similar number of walking bouts per day compared with the young individuals. The energetic cost of basal metabolic rate, thermic effect of food, total daily energy expenditure, and nonexercise activity thermogenesis were not different between the elderly and young groups. Thus, the energetic cost of walking in the elderly may be greater than in the young. Lean, healthy elderly individuals may have a biological drive to be less active than the young.     

The effect of uphill and downhill walking on gait parameters: A self-paced treadmill study

It has been shown that gait parameters vary systematically with the slope of the surface when walking uphill (UH) or downhill (DH) (Andriacchi et al., 1977; Crowe et al., 1996; Kawamura et al., 1991; Kirtley et al., 1985; McIntosh et al., 2006; Sun et al., 1996). However, gait trials performed on inclined surfaces have been subject to certain technical limitations including using fixed speed treadmills (TMs) or, alternatively, sampling only a few gait cycles on inclined ramps. Further, prior work has not analyzed upper body kinematics. This study aims to investigate effects of slope on gait parameters using a self-paced TM (SPTM) which facilitates more natural walking, including measuring upper body kinematics and gait coordination parameters.Gait of 11 young healthy participants was sampled during walking in steady state speed. Measurements were made at slopes of +10°, 0° and −10°. Force plates and a motion capture system were used to reconstruct twenty spatiotemporal gait parameters. For validation, previously described parameters were compared with the literature, and novel parameters measuring upper body kinematics and bilateral gait coordination were also analyzed.Results showed that most lower and upper body gait parameters were affected by walking slope angle. Specifically, UH walking had a higher impact on gait kinematics than DH walking. However, gait coordination parameters were not affected by walking slope, suggesting that gait asymmetry, left-right coordination and gait variability are robust characteristics of walking. The findings of the study are discussed in reference to a potential combined effect of slope and gait speed. Follow-up studies are needed to explore the relative effects of each of these factors.     

Energetics and passive dynamics of the ankle in downhill walking

This study investigated the energetics of the human ankle during the stance phase of downhill walking with the goal of modeling ankle behavior with a passive spring and damper mechanism. Kinematic and kinetic data were collected on eight male participants while walking down a ramp with inclination varying from 0° to 8°. The ankle joint moment in the sagittal plane was calculated using inverse dynamics. Mechanical energy injected or dissipated at the ankle joint was computed by integrating the power across the duration of the stance phase. The net mechanical energy of the ankle was approximately zero for level walking and monotonically decreased (i.e., became increasingly negative) during downhill walking as the slope decreased. The indication is that the behavior of the ankle is energetically passive during downhill walking, playing a key role in dissipating energy from one step to the next. A passive mechanical model consisting of a pin joint coupled with a revolute spring and damper was fit to the ankle torque and its parameters were estimated for each downhill slope using linear regression. The passive model demonstrated good agreement with actual ankle dynamics as indicated by low root-mean-square error values. These results indicate the stance phase behavior of the human ankle during downhill walking may be effectively duplicated by a passive mechanism with appropriately selected spring and damping characteristics.     

New assistive walker improved local dynamic stability in young healthy adults

In this study, we investigated the effect of walker type on gait pattern characteristics comparing normal gait (NG), gait with a regular walker (RW), and gait with a newly developed walker with vertical moveable handlebars, the Crosswalker (CW).Partial weight bearing (PWB) of the feet, peak joint angles and largest Lyapunov exponent (λ_max) of the lower extremities (hip, knee, ankle) in the sagittal plane, and gait parameters (gait velocity, stride length, cadence, stride duration) were determined for 18 healthy young adults performing 10 walking trials for each walking condition. Assistive gait with the CW improved local dynamic stability in the lower extremities (hip, knee, ankle) compared with RW and was not significantly different from NG. However, peak joint angles and stride characteristics in CW were different from NG. The PWB on the feet was lower with the RW (70.3%) compared to NG (82.8%) and CW (80.9%). This improved stability may be beneficial for the elderly and patients with impaired gait. However, increased PWB is not beneficial for patients during the early stages of rehabilitation.     

A model of cerebrocerebello-spinomuscular interaction in the sagittal control of human walking

A computationally developed model of human upright balance control (Jo and Massaquoi on Biol cybern 91:188–202, 2004) has been enhanced to describe biped walking in the sagittal plane. The model incorporates (a) non-linear muscle mechanics having activation level -dependent impedance, (b) scheduled cerebrocerebellar interaction for control of center of mass position and trunk pitch angle, (c) rectangular pulse-like feedforward commands from a brainstem/ spinal pattern generator, and (d) segmental reflex modulation of muscular synergies to refine inter-joint coordination. The model can stand when muscles around the ankle are coactivated. When trigger signals activate, the model transitions from standing still to walking at 1.5 m/s. Simulated natural walking displays none of seven pathological gait features. The model can simulate different walking speeds by tuning the amplitude and frequency in spinal pattern generator. The walking is stable against forward and backward pushes of up to 70 and 75 N, respectively, and with sudden changes in trunk mass of up to 18%. The sensitivity of the model to changes in neural parameters and the predicted behavioral results of simulated neural system lesions are examined. The deficit gait simulations may be useful to support the functional and anatomical correspondences of the model. The model demonstrates that basic human-like walking can be achieved by a hierarchical structure of stabilized-long loop feedback and synergy-mediated feedforward controls. In particular, internal models of body dynamics are not required.     

Stick insects walking along inclined surfaces

In the experiments stick insects walk on an inclined substratesuch that the legs of one side of the body point uphill andthe legs of the other side point downhill. In this situationthe vertical axis of the body is rotated against the inclinationof the substrate as if to compensate for the effect of substrateinclination. A very small effect has been found when the experimentwas performed with animals standing on a tilted platform whichshows that the effect depends on the behavioral context. When,however, animals first walked along the inclined surface andthen, before measurement, stopped walking spontaneously, a rotationof the body has been observed similar to that in walking animals.In a second experiment it was tested whether the observed bodyrotation is caused by the change of direction of gravity vectoror by the fact that on an inclined surface gravity necessarilyhas a component pulling the body sideways. Experiments withanimals standing on horizontal ground and additional weightsapplied pulling the body to the side showed similar body rotationssupporting the latter idea. In a simulation study it could beshown that the combined activity of proportional feedback controllersin the leg joints is sufficient to explain the observed behavior.This is however only possible if the gain factors of coxa-trochanterjoint controller and of femur-tibia joint controller show aratio in the order of 1 : 0.05 to 1 : 1.8. In order to describethe behavior of animals standing on a tilted platform, a ratioof 1 : 1.7 is necessary. In walking animals, this body rotationrequires to change the trajectories of stance and swing movements.The latter have been studied in more detail. During swing, thefemur-tibia joint is more extended in the uphill legs. Conversely,the coxa-trochanter joint appears to be more elevated in thedownhill legs which compensates the smaller lift in the femur-tibiajoint. The results are discussed in the context of differenthypotheses.     

The relationship between physical fitness and ambulatory activity in very elderly women with normal functioning and functional limitations

The effect of daily ambulatory activity on physical fitness has not yet been identified by quantitatively measuring the time spent on the intensity levels of ambulatory activity in elderly women over 75 with different functional capacity levels. The subjects consisted of 147 elderly women over 75 years old (82.8±4.3 years old) who were all capable of performing basic daily activities by themselves. Physical fitness was measured for 7 items (handgrip strength, knee extensor strength, postural stability, stepping, one-legged standing time with eyes open, 10 m walking, and the Timed Up and Go Test). The subjects wore a triaxial accelerometer for 2 consecutive weeks to measure their daily physical activities. The functional capacity level was assessed by the Tokyo Metropolitan Institute of Gerontology Index of Competence. The subjects were divided into two groups, a group with a score ≥10 points (high functional capacity group, n=59) and a score <10 points (low functional capacity group, n=88), and the relationship between physical fitness and physical activity was examined in both groups. In both the high and low functional capacity groups, 10 m walking, the Timed Up and Go Test, and one-legged standing time with eyes open significantly correlated with either the total steps/day or the ambulatory activity intensity. In the high functional capacity group, the knee extensor strength also significantly correlated with the total steps/day and moderate ambulatory activity. It is suggested that very elderly women with a reduced functional capacity should maintain their mobility by simply increasing their daily ambulatory activity.     

Kinematics and muscle activities of the lumbar spine during and after working in stooped postures

Existing biomechanical evidence suggests mechanisms of low back injuries and disorders associated with prolonged stooping. However, no research has tested realistic and more natural stooped work conditions with human subjects in the investigation of the biomechanical responses of the low back in prolonged stooping. The current study was aimed to explore various biomechanical responses of the low back in more realistic and work-related loading and posture conditions of prolonged stooping. Twenty two subjects performed stooped work tasks for 7 min with periodic micro-breaks in upright standing, and various measures for assessing biomechanical responses of the low back were obtained before, during and immediately after the stooped work period. Study results found significant increases (p < 0.05) in the range of lumbar flexion and myoelectric activation of the low back muscles after the stooped work period. During stooped work, the low back extensor muscles did not show flexion–relaxation. It could be concluded that the natural and unrestricted stooped work conditions produced similar viscoelastic responses of the low back to what more severe stooping conditions with posture restrictions did in previous research, but could be more fatigue-prone due to low but consistent activation of the low back extensor muscles during stooped work activities.     

Patient controlled electrical stimulation via EMG signature discrimination for providing certain paraplegics with primitive walking functions

In this paper we present the first patient-based results for a micro computer-based EMG signature-controlled functional electrical stimulation (FES) system, for restoring walker-supported and brace-free primitive walking to complete paraplegics, at the patients own command. Stimulation is thus controlled directly by the patient's own EMG signatures, generated by him at will, and which are produced by him at his erector spinae back muscles (while activating these muscles more or less as he would during normal walking, had the person not been a paraplegic). In this manner a switch-free simplistic but reliable information-gap is produced across the paraplegic's lesion, such that the above lesion's relatively normal EMG provides the control command to electrical stimulation of paralyzed peripheral (lower limb) nerves, to provide the basic functions of standing up, sitting-down and walking. The FES signals are at pulse rates close to the average ones occurring naturally at the corresponding nerves. The paper reports actual patient results for 3 paraplegics, two at T-9 (one complete, one with only residual sensation) and one T-6 complete paraplegic, who all subsequently achieved walking between parallel bars and two even with a walker (no braces in all cases), using the FES system, this walking being, to our knowledge the first hand-switch-free patient-controlled FES walking reported ever. The EMG signature-discrimination for control is as previously developed by D. Graupe for artificial-limb control, and it depends only on the EMG signature temporal parameters, while completely ignoring EMG power (amplitude) level. Whereas all 3 patients produced EMG parameters in the range reported below, adequate for controlling all functions involved, only one, a T-6 complete paraplegic, has so far (due to time limitations) achieved EMG controlled walking between parallel bars and by now also a few steps with a walker. One T-9 complete paraplegic, injured 5 years before coming to our program, was however able, within 4 weeks, to walk via FES with a walker, though with manual control. Note that the present approach is valid only for upper motor neuron paralysis situations (intact peripheral nerves and muscles). We are thus also attempting to apply this approach to certain hemiplegics and quadraplegics, for restoring some upper limb functions, using EMG signals from the trapezius (shoulder) level.     

Correlates of upper and lower body muscular strength in children

Despite the widespread use of and acceptance of muscular fitness field tests in national youth fitness test batteries, little is known about how these field tests compare to 1 repetition maximum (1RM) strength in children. Therefore, the aim of this study was to characterize and identify correlates of muscular strength in children 7 to 12 years of age. Ninety children (39 girls and 51 boys) between the ages of 6.7 and 12.3 years volunteered to participate in this study. Children were tested on 1RM chest press (CP) strength, 1RM leg press (LP) strength, handgrip strength, vertical jump, long jump, sit and reach flexibility, and height and weight (used to determine body mass index [BMI]). For the combined sample, LP 1RM ranged from 75% to 363% of body weight and CP 1RM ranged from 25% to 103% of body weight. Multiple regression analyses predicting LP 1RM showed that BMI and long jump were significant (R = 44.4% with age and gender not significant) and BMI and vertical jump were significant (R = 40.8% with age and gender not significant). Multiple regression analyses predicting CP 1RM showed that BMI and handgrip strength were significant (R = 58.6% with age and gender not significant). Age and gender alone accounted for 4.6% (not significant) of the variation in LP 1RM and 15.4% (significant) in CP 1RM. In summary, these data indicate that BMI, handgrip strength, long jump, and vertical jump relate to 1RM strength in children and therefore may be useful for assessing muscular fitness in youths.     

Energy efficient walking with central pattern generators: from passive dynamic walking to biologically inspired control

Like human walking, passive dynamic walking—i.e. walking down a slope with no actuation except gravity—is energy efficient by exploiting the natural dynamics. In the animal world, neural oscillators termed central pattern generators (CPGs) provide the basic rhythm for muscular activity in locomotion. We present a CPG model, which automatically tunes into the resonance frequency of the passive dynamics of a bipedal walker, i.e. the CPG model exhibits resonance tuning behavior. Each leg is coupled to its own CPG, controlling the hip moment of force. Resonance tuning above the endogenous frequency of the CPG—i.e. the CPG’s eigenfrequency—is achieved by feedback of both limb angles to their corresponding CPG, while integration of the limb angles provides resonance tuning at and below the endogenous frequency of the CPG. Feedback of the angular velocity of both limbs to their corresponding CPG compensates for the time delay in the loop coupling each limb to its CPG. The resonance tuning behavior of the CPG model allows the gait velocity to be controlled by a single parameter, while retaining the energy efficiency of passive dynamic walking.     

An application of scissored-pair control moment gyroscopes in a design of wearable balance assistance device for the elderly

Impaired balance control ability and degraded functional mobility increases the risk of falling in elderly people. The elderly show more postural sway when standing compared with young people. A sway fall occurs when the center of gravity moves outside the limit of stability. In order to reduce the fall risk from the excessive sway, this study presents the design of wearable balance assistance device for the elderly. Scissored-pair control moment gyroscopes were selected as a torque actuator. A two-axis inclination sensor was used to detect the inclined angle of the wearer’s body. The direction of sway was calculated from the detected inclined angle. The designed device weighs 8.2 kg with a height of 32 cm × width of 40 cm × depth of 22 cm. A multi-segment model of a standing human was used to investigate the device’s performance for balance recovery. According to the simulations, balance recovery in any direction was successfully accomplished with the appropriate initial angle. The relationship between the effective initial angle and detected inclined angle was subsequently established. The stability provided by activation of the device was able to limit the unstable user’s sway boundary. The designed device shows promise for use as a balance assistance device for the elderly.     

Redistribution of intra- and inter-limb support moments during downhill walking on different slopes

Downhill walking presents a greater risk of falling as a result of slipping or loss of balance in comparison with level walking. The current study aimed to investigate the effects of inclination angles on the intra-limb (inter-joint) and inter-limb sharing of the body support during downhill walking for a better understanding of the associated control strategy. Fifteen young male adults (age: 32.6±5.2 years, height: 168.9±5.5 cm, mass: 68.4±8.7 kg) performed level and downhill walking while their kinematic and kinetic data were measured for calculating joint moments and total support moments of the lower limbs using inverse dynamics analysis. The peak total support moments of both the leading and trailing limbs increased with increasing inclination angles (p<0.05) with different sharing patterns among individual joints. Being the major contributor to the peak total support moment during early single-limb support, the contribution of the knee remained unaltered (p>0.05), but the contributions of the hip increased with reduced contributions from the ankle (p<0.05). For the increased peak total support moment during late single-limb support, the intra-limb sharing changed from a major ankle contribution to a major knee contribution strategy. The hip contribution was also increased (p<0.05) but the hip flexor moment remained unaltered (p>0.05). During double-limb support, the main contributor to the whole body support changed from the trailing limb to the leading limb with increasing inclination angles (p<0.05).     

Subject-specific responses to an adaptive ankle prosthesis during incline walking

Individuals with lower-limb amputation often have difficulty walking on slopes, in part due to limitations of conventional prosthetic feet. Conventional prostheses have fixed ankle set-point angles and cannot fully replicate able-bodied ankle dynamics. Microprocessor-controlled ankles have been developed to help overcome these limitations. The objective of this study was to characterize how the slope adaptation feature of a microprocessor-controlled ankle affected individual prosthesis user gait biomechanics during sloped walking. Previous studies on similar microprocessor-controlled ankles have focused on group-level results (inter-subject mean), but did not report individual subject results. Our study builds upon prior work and provides new insight by presenting subject-specific results and investigating to what extent individual responses agree with the group-level results. We performed gait analysis on seven individuals with unilateral transtibial amputation while they walked on a 7.5° incline with a recently redesigned microprocessor-controlled ankle that adjusts ankle set-point angle to the slope. We computed gait kinematics and kinetics, and compared how users walked with vs. without this set-point adjustment. The microprocessor-controlled ankle increased minimum toe clearance for all subjects. Despite the microprocessor-controlled ankle behaving similarly for each user, we observed marked differences in individual responses. For instance, two users switched from a forefoot landing pattern with the microprocessor-controlled ankle locked at neutral angle to rearfoot landing when the microprocessor-controlled ankle adapted to the slope, while two maintained a forefoot and three maintained a rearfoot landing pattern across conditions. Changes in knee angle and moment were also subject-specific. Individual user responses were often not well represented by inter-subject mean. Although the prevailing experimental paradigm in prosthetic gait analysis studies is to focus on group-level analysis, our findings call attention to the high inter-subject variability which may necessitate alternative experimental approaches to assess prosthetic interventions.     

Age-related changes in the behavior of the muscle-tendon unit of the gastrocnemius medialis during upright stance

Mechanical properties of the muscle-tendon unit change with aging, but it is not known how these modifications influence the control of lower leg muscles during upright stance. In this study, young and elderly adults stood upright on a force platform with and without vision while muscle architecture and myotendinous junction movements (expressed relative to the change in the moment on the x-axis of the force platform) were recorded by ultrasonography and muscle activity by electromyography. The results show that the maximal amplitude of the sway in the antero-posterior direction was greater in elderly adults (age effect, P < 0.05) and was accompanied by an increase in lower leg muscle activity compared with young adults. Moreover, the data highlight that fascicles shorten during forward sway and lengthen during backward sways but more so for young (-4 ± 3 and -4 ± 3 mm/Nm, respectively) than elderly adults (-0.7 ± 3 and 0.8 ± 3 mm/Nm, respectively; age × sway, P < 0.001). Concurrently, the pennation angle increased and decreased during forward and backward sways, respectively, with greater changes in young than elderly adults (age × sway, P < 0.001). In contrast, no significant differences were observed between age groups for tendon lengthening and shortening during sways. The results indicate that, compared with young, elderly adults increase the stiffness of the muscular portion of the muscle-tendon unit during upright stance that may compensate for the age-related decrease in tendon stiffness. These observations suggest a shift in the control strategy used to maintain balance.     

Muscle post-effects and upright standing in healthy subjects and patients with sensory-motor integration disorders

We compared the upright standing in 7 patients with sensory-motor disorders and 7 healthy subjects (control) before and after 30-s involuntary neck muscle contraction. A trajectory of the center of pressure was recorded during 30-s standing with the eyes open, eyes closed and standing on a foam-rubber with the eyes open. As compared to healthy subjects, patients exhibited an increased body sway area during standing with the eyes open on both the firm surface and foam-rubber and a backward shift of the center of pressure during standing with the eyes both open and closed. Closing the eyes affected the upright standing of patients to a lesser extent than standing of healthy subjects. Involuntary neck muscle contraction within 30 s elicited a backward shift of the center of pressure in healthy subjects, especially during standing with the eyes closed, and a decrease in the length of the center-of-pressure trajectory, especially of its frontal component during standing on the foam-rubber. In patients, a post-effect of the neck muscle contraction manifested itself as a decrease in the body sway area during standing on the foam-rubber and relative increase in the frontal component of the center-of-pressure trajectory during standing with the eyes closed. The results suggest that the upright standing of patients with sensory-motor disorders is more sensitive to somatosensory than visual input, and 30-s neck muscle contraction approach their postural stability to the age-matched control.