Differences between trunk sway characteristics on a foam support surface and on the Equitest ankle-sway-referenced support surface.

Trunk sway measures of postural stability during clinical balance tests: effects of a unilateral vestibular deficit.

Postural Effects of the Scaled Display of Visual Foot Center of Pressure Feedback Under Different Somatosensory Conditions at the Foot and the Ankle

Purpose. This study aimed to evaluate the effects of prosthetic foot types on the postural stability among transtibial amputees when standing on different support surfaces. Materials and Methods. The postural stability of 10 transtibial amputees wearing solid ankle cushion heel (SACH) foot, single-axis (SA) foot, and energy-saving and return (ESAR) foot was assessed. Results were compared with able-bodied participants. Anterior-posterior stability index (APSI), mediolateral stability index (MLSI), and overall stability index (OSI) were measured by computed posturography in an upright stance on firm, foam, and unstable support surfaces. Results. The mean OSI score of SACH foot was significantly lower than that of an ESAR foot when the participants were standing on a compliant surface. When compared to able-bodied group, MLSI score was significantly higher for each of the prosthetic foot groups while OSI score was significantly higher for ESAR foot only in foam condition. Conclusions. Differences between prosthetic foot types and groups (amputees versus able-bodied) can only be distinguished when individuals were standing on a compliant surface. Amputees exhibited an increased postural instability in the mediolateral direction than able-bodied individuals. Hence, the restoration of stability in the frontal plane and the enhancement of proprioception at the residual limb should be the basis of rehabilitation programs.

Background: Recently, the oscillatory bar has been proposed as a new and effective rehabilitation tool in people with nonspecific low back pain (NSLBP), although its effects on muscular control in this population have not been well documented, especially in lower extremity muscles and different support surface conditions.Objective: This study aimed to evaluate and compare the effects of flexi-bar use on stable and unstable surfaces on electromyographic activity of trunk and lower extremity muscles in healthy persons and those with NSLBP.Material and Methods: 18 healthy men and 18 men with NSLBP participated in this cross-sectional study. The root mean square value of electromyographic activity was calculated in the trunk and lower extremity muscles during 4 different task conditions: quiet standing (QS) or flexi-bar use on a rigid or foam support surface. A repeated measures test was used for statistical analysis. Results: The results showed that the amplitude activity of almost all muscles was significantly greater during flexi-bar use than in the QS condition (P<0.05). The rectus femoris, tibialis anterior, and gastrocnemius demands were significantly greater on the foam than the rigid surface (P<0.05).Conclusion: This study showed that oscillatory forces caused by flexi-bar use can increase muscle activation in multiple segments (hip and ankle in addition to trunk muscles) that are crucial for postural stability. Furthermore, the foam surface appeared to target the rectus femoris in addition to the ankle muscles. Using a flexi-bar may be helpful in NSLBP rehabilitation, and exercising on a foam surface may enhance additive hip muscle activity in people with NSLBP.

Directional effects of biofeedback on trunk sway during stance tasks in healthy young adults

Vestibular deficit patients have an increased fall risk and fear of falling. Postural threat, known to increase balance-related fear and anxiety, influences vestibular gains during quiet standing in young healthy adults. The current study examined whether there is a similar relationship for peripheral unilateral vestibular loss (UVL) patients in comparison to age-matched healthy controls (HC). University laboratory. Prospective laboratory study. Eleven UVL patients, nine with vestibular neurectomy. Eleven aged-matched HCs. Subjects stood on a hydraulic lift placed at two heights: low (0.8 m, away from the edge) and high (3.2 m, at the edge). Amplitude (root mean square), mean power frequency (MPF), and mean position were analyzed for center of foot pressure (COP) and 90% ranges for angle amplitude and velocity for trunk sway. Group interactions were strongest for anterior-posterior (AP) COP and trunk pitch angle. AP lean away from the edge was greater in HCs than UVLs. HCs, but not UVLs had a decrease in root mean square AP COP with height. Trunk pitch sway was changed similarly. Both groups had increased trunk pitch velocity at height. Changes with height were less for roll: MPF of lateral COP increased with height for UVLs with no changes for HCs, and trunk roll amplitude decreased for both groups. This report provides evidence for a differential effect of height induced postural threat on balance control between UVLs and HCs presumably due to the reduced vestibular-spinal gain in UVL subjects.

The findings of this study may serve as a basis for designing informed patient-specific balance rehabilitation programs and strategies to improve stability and minimize falls in patients with distal radius fractures. The integrative methodology presented in this work can be extended to postural control and balance assessment for various orthopaedic/neurological conditions.

This study was designed to provide evidence for the hypothesis that human balance corrections in response to pitch perturbations are controlled by muscle action mainly about the ankle and knee joints, whereas balance corrections for roll perturbations are controlled predominantly by motion about the hip and lumbro-sacral joints. A dual-axis rotating support surface delivered unexpected random perturbations to the stance of 19 healthy young adults through eight different directions in the pitch and the roll planes and three delays between pitch and roll directions. Roll delays with respect to pitch were no delay, a short 50-ms delay of roll with respect to pitch movements, (chosen to correspond to the onset time of leg muscle stretch reflexes), and a long 150-ms delay between roll and pitch movements (chosen to shift the time when trunk roll velocity peaks to the time when trunk peak pitch velocity normally occurs). Delays of stimulus roll with respect to pitch resulted in delayed roll responses of the legs, trunk, arms, and head consistent with stimulus delay without any changes in roll velocity amplitude. Delayed roll perturbations induced only small changes in the pitch motion of the legs and trunk; however, major changes were seen in the time when roll motion of the trunk was arrested. Amplitudes and directional sensitivity of short-latency (SL) stretch reflexes in ankle muscles were not altered with increasing roll delay. Small changes to balance correcting responses in ankle muscles were observed. SL stretch reflexes in hip and trunk muscles were delayed, and balance-correcting responses in trunk muscles became split into two distinct responses with delayed roll. The first of these responses was small and had a directional responsiveness aligned more along the pitch plane. The main, larger, response occurred with an onset and time-to-peak consistent with the delay in trunk roll displacement and its directional responsiveness was roll oriented. The sum of the amplitudes of these two types of balance-correcting responses remained constant with roll delay. These results support the hypothesis that corrections of the body's pitch and roll motion are programmed separately by neural command signals and provide insights into possible triggering mechanisms. The evidence that lower leg muscle balance-correcting activity is hardly changed by delayed trunk roll also indicates that lower leg muscle activity is not predominant in correcting roll motion of the body. Lower leg and trunk muscle activity appears to have a dual action in balance corrections. In trunk muscles the main action is to correct for roll perturbations and the lesser action may be an anticipatory stabilizing reaction for pitch perturbations. Likewise, the small changes in lower leg muscle activity may result from a generalized stabilizing reaction to roll perturbations, but the main action is to correct for pitch perturbations.

Objective:The purpose of this study was to measure muscle activation during ascending and descending phases of the push-up exercise on both stable and unstable support surfaces.Participants:Fourteen asymptomatic male amateur badminton players. During push-up exercises on stable and unstable bases, muscle activation measurements were collected with phase divisions (ascending and descending phase).Methods:Electromyography (EMG) was utilized to measure activation of the upper trapezius (UT) and lower trapezius (LT), middle serratus anterior (MSA) and lower serratus anterior (LSA), pectoralis major (PM), and triceps brachii (TB) muscles.Results:An unstable support surface produced significantly greater activation of the UT, LT, LSA, and PM muscles than a stable support surface (p &lt; 0.05). The MSA, LSA, TB, and PM muscles demonstrated greater activation during the ascending phase than the descending phase of the push-up exercise (p &lt; 0.05).Conclusions:The unstable support surface appeared to produce relatively greater activation of the LSA than that of the MSA. The descending phase of the push-up did not demonstrate a higher level of activation for any of the muscles tested.

Purpose: The purpose of this study was to investigate the effects of core muscle strengthening training and core exercise on unstable support on the balance and performance of a shooter. Methods: Fourteen athletes were randomly assigned to perform core muscle strength training for seven athletes, and seven athletes were exercised on an unstable surface. Two groups were conducted three times a week for 20 minutes. Static balance, dynamic balance, and shooting scores were measured before and after the experiment. Results: There was a statistically significant difference in static balance, dynamic balance in the group trained on the unstable support surface (p<.05). Conclusion: Based on this experiment, it can be seen that the balance training of the shooter on the unstable support surface is more effective than the balance of other methods.

Normal young children ranging in age from 1 1/2 to 10 years were assessed in a number of experimental paradigms testing the ability to adapt quickly their strategy of control to altered support surface and visual conditions. The experimental protocols, using a movable platform and visual surround, and the analytic techniques, using EMGs and measures of reaction forces and body motions, were identical to those employed in a complementary study in this issue (Nashner, L. M., F. O. Black, and C. Wall, III (1982) J. Neurosci. 2: 536-544). The structure of automatic postural adjustments in young children was, with the exception of greater variability, similar to that of adult subjects studied previously. However, young children below the age of 7 1/2 years were unable to suppress systematically the influence of inputs derived from the support surface or from vision when these provided inappropriate orientation information due to the motion of these surfaces. The discussion emphasizes that the automatic postural adjustments and the context-dependent reweighting of support surface, vestibular, and visual inputs are organizationally separate processes and that the hierarchically lower level automatic process matures before the higher level adaptive processes.

The purpose of this study was to assess the influence of electrotactile feedback on postural control performance during binaural galvanic vestibular stimulation (GVS). Postural equilibrium was measured with a computerized hydraulic platform in 10 healthy adults (6M, 4F, 24-65 y). Feedback of anterior-posterior (AP) and mediallateral (ML) body sway was derived from a 2-axis linear accelerometer mounted on a torso belt and displayed on a 144-point electrotactile array held against the anterior dorsal tongue. Subjects were trained to use the tongue electrotactile feedback (TEF) by voluntarily swaying to draw figures on their tongue, both with and without GVS. Subjects performed 24 randomized trials (20-s duration with eyes closed, 2 trials per condition), including 4 support surface conditions (fixed, rotational sway-referenced, translating the support surface proportional to AP sway, and combined rotational-translational support-platform sway referencing), and 3 feedback conditions (baseline, GVS, and GVS with TEF). Postural performance was assessed using deviations from upright (peak-to-peak and root-mean-square sway) and convergence toward stability limits (time and distance to limit of support boundaries). Postural stability was impaired (with respect to baseline) during GVS in all platform conditions, with larger decrements in performance during trials with rotation sway-referencing. Electrotactile feedback improved performance with GVS toward non-GVS levels, especially during trials with rotation sway-referencing. These results demonstrate the effectiveness of TEF in providing sensory substitution to maintain postural stability during vestibular disturbances.

The vertical posture was studied during standing with fееt on the support surfaces of different structures. The movements of the center of pressure (CP) of each leg and the common CP (CCP) were recorded while the subject stood with a support on a smooth floor and with the support of one foot on a spike mat (SM) with different load distributions between the legs. When the body weight was transferred to one leg during standing under ordinary conditions on a smooth floor, the CP of the loaded leg moved more than the CP of the unloaded leg; i.e., the posture sway was compensated mainly due to the activity of the loaded leg, which created a larger torque. When the subject stood with one foot on the SM, the CP movement of this leg did not depend on the leg load and was about 60% of the CP movement of the leg on the smooth floor. Apparently, the CP displacement of the unloaded leg on smooth support was larger than the CP displacement of the loaded leg creating the torque necessary for compensating the body sway. Thus, maintaining the vertical posture was carried out mainly by the leg standing on the smooth support. It is assumed that additional stimulation of different surface and deep receptors of the foot caused by foot support on the SM hampered the perception of its CP position, and the vertical posture was maintained mainly by the leg afferent signals from which more precisely reflected the CP position.

One of the signatures of balance deficits observed in vestibular loss subjects is the greater instability in the roll compared to pitch planes. Directional differences in the timing and strengths of vestibular and proprioceptive sensory signals between roll and pitch may lead to a greater miscalculation of roll than pitch motion of the body in space when vestibular input is absent. For this reason, we compared the timing and amplitude of vestibular information, (observable in stimulus-induced head accelerations when subjects are tilted in different directions), with that of proprioceptive information caused by stimulus induced rotations of ankle and hip joints [observable as short latency (SL) stretch responses in leg and trunk muscle EMG activity]. We attempted to link the possible mode of sensory interaction with the deficits in balance control. Six subjects with bilaterally absent vestibular function and 12 age-matched controls were perturbed, while standing, in 8 directions of pitch and roll support surface rotation in random order. Body segment movements were recorded with a motion analysis system, head accelerations with accelerometers, and muscle activity with surface EMG. Information on stimulus pitch motion was available sequentially. Pitch movements of the support surface were best coded in amplitude by ankle rotation velocity, and by head vertical linear acceleration, which started at 13 ms after the onset of ankle rotation. EMG SL reflex responses in soleus with onsets at 46 ms provided a distal proprioceptive correlate to the pitch motion. Roll information on the stimulus was available simultaneously. Hip adduction and lumbo-sacral angular velocity were represented neurally as directionally specific short latency stretch and unloading reflexes in the bilateral gluteus medius muscles and paraspinal muscles with onsets at 28 ms. Roll angular accelerations of the head coded roll amplitude and direction at the same time (31 ms). Significant differences in amplitude coding between vestibular loss subjects and controls were only observed as a weaker coding between stimulus motion and head roll and head lateral linear accelerations. The absence of vestibular inputs in vestibular loss subjects led to characteristic larger trunk in motion in roll in the direction of tilt compared to pitch with respect to controls. This was preceded by less uphill flexion and no downhill extension of the legs in vestibular loss subjects. Downhill arm abduction responses were also greater. These results suggest that in man vestibular inputs provide critical information necessary for the appropriate modulation of roll balance-correcting responses in the form of stabilising knee and arm movements. The simultaneous arrival of roll sensory information in controls may indicate that proprioceptive and vestibular signals can only be interpreted correctly when both are present. Thus, roll proprioceptive information may be interpreted inaccurately in vestibular loss subjects, leading to an incorrect perception of body tilt and insufficient uphill knee flexion, especially as cervico-colic signals appear less reliable in these subjects as an alternative sensory input.

Core muscle activity during suspension exercises