Neck vibration causes short-latency electromyographic activation of lower leg muscles in postural reactions of the standing human

Does vibration frequency and location influence the effect of neck muscle vibration on postural sway? A cross-sectional study in asymptomatic participants

INTRODUCTION

Postural control is of utmost importance for human functioning. Cervical proprioception is crucial for balance control. Therefore, any change to it can lead to balance problems. Previous studies used neck vibration to change cervical proprioception and showed changes in postural control, but it remains unknown which vibration frequency or location causes the most significant effect. Therefore, this study aimed to investigate the effect of different vibration frequencies and locations on postural sway and to serve as future research protocol guidance.

METHODS

Seventeen healthy young participants were included in the study. We compared postural sway without vibration to postural sway with six different combinations of vibration frequency (80, 100, and 150 Hz) and location (dorsal neck muscles and sternocleidomastoid). Postural sway was evaluated using a force platform. The mean center of pressure (CoP) displacement, the root mean square (RMS), and the mean velocity in the anteroposterior and mediolateral direction were calculated, as well as the sway area. The aligned rank transform tool and a three-way repeated measures ANOVA were used to identify significant differences in postural sway variables.

RESULTS

Neck vibration caused a significant increase in all postural sway variables (p < 0.001). Neither the vibration frequency (p > 0.34) nor location (p > 0.29) nor the interaction of both (p > 0.30) influenced the magnitude of the change in postural sway measured during vibration.

CONCLUSION

Neck muscle vibration significantly changes CoP displacement, mean velocity, RMS, and area. However, we investigated and found that there were no significant differences between the different combinations of vibration frequency and location.

The effect of foot posture on static balance, ankle and knee proprioception in 18-to-25-year-old female student: a cross-sectional study

BACKGROUND & PURPOSE

Afferent input from the sole affects postural stability. Cutaneous reflexes from the foot are important to posture and gait. Lower-limb afferents alone provide enough information to maintain upright stance and are critical in perceiving postural sway. Altered feedback from propreoceptive receptors alters gait and patterns of muscle activation. The position and posture of the foot and ankle may also play an important role in proprioceptive input.Therefore, the current research aims to compare static balance and ankle and knee proprioception in people with and without flexible flatfeet.

METHODOLOGY

91 female students between the ages of 18 and 25 voluntarily participated in this study, of which 24 were in the flexible flatfoot group and 67 were in the regular foot group after evaluating the longitudinal arch of the foot. The position sense of ankle and knee joints were measured using the active reconstruction test of the ankle and knee angle; Static balance was measured using the Sharpened Romberg test. Data were non-normally distributed. Accordingly, non-parametric tests were applied. The Kruskal-Wallis test was applied to compare differences between groups in variables.

RESULT

Kruskal-Wallis test showed a significant difference between two groups of flat feet and normal feet in the variables of static balance and position sense of ankle plantarflexion, ankle dorsiflexion, and knee flexion (p ≤ 0.05). A significant correlation was found between static balance and sense of ankle and knee position in the group with normal feet. The analysis of the regression line also showed that ankle and knee position sense could predict the static balance score in the regular foot group (ankle dorsiflexion position sense 17% (R² = 0.17), ankle plantarflexion position sense 17% (R² = 0.17) and knee flexion position sense 46% (R² = 0.46) explain of changes in static balance).

DISCUSSION & CONCLUSION

Flexible flatfoot soles can cause loss of balance and sense of joint position; therefore, according to this preliminary study, clinicians must be aware and should take into account this possible deficit in the management of these patients.

Perception of gait motion during multiple lower-limb vibrations in young healthy individuals: a pilot study

In virtual reality (VR), immersion can be created through synchronous visuomotor stimulations and enhanced by adding auditory or kinesthetic stimulations. Multiple patterned vibrations applied at the lower limbs might be a way to induce kinesthetic perception of gait motion that could be combined with VR stimulations to add the perception of self-motion. However, gait motion perception using multiple vibrations has not yet been evaluated. The objective of the study was to quantify the perception of gait motion while applying multiple, patterned vibrations to the lower limbs in healthy individuals. Twenty young healthy participants (25.1 ± 4.4 years) experienced multiple vibrations in 1-min trials. Stimulation consisted of a vibration pattern based on the sequence of muscle lengthening during a 2-s gait cycle. Stimulation was applied on participants in a standing position, under 11 experimental conditions controlling visual information (eyes open/closed), vibration frequency (40-80 Hz), and number and location of the joints stimulated (hips, knees, ankles isolated or combined two by two). Perception of gait motion was quantified for each condition using a 10-point visual analog scale (VAS, 0: "no perception", 10: "Perception of gait movements"). All participants except one achieved a score higher than 5/10 in at least one condition. Great variability was found for perception of gait motion within participants and conditions (VAS ranging from 0 to 9.6/10). Differences were found between conditions (p < 0.01), with higher mean and median scores in conditions that included knee vibration. Inducing gait motion perception is possible using multiple vibrations in healthy individuals. Stimulation of the knees seems to positively influence perception of gait motion.

Muscle activity during backward perturbation response in patients with clinical vertebral compression fractures

The present study examined muscle activity in response to backward perturbation in patients with clinical vertebral compression fracture (CVCF). The subjects were 32 patients aged 65 years and above consisting of 16 each with (CVCF group) and without (control group) CVCF. The time to peak activity, and time of onset of muscle activity of the anterior tibial, vastus medialis, and rectus abdominis muscles when unexpected backward perturbation was applied were evaluated by surface electromyography. The strength of perturbation was 4% or 6% of the subject's body weight. In addition, the presence of the stepping reaction to perturbation, severity of low back pain, and vertebral alignment were evaluated. Each item was compared between the two groups. In the CVCF group, kyphosis and severity of low back pain were significantly more severe, the time to peak activity of the anterior tibial muscle after the application of perturbation at 6% of the body weight was significantly shorter, and the time of onset of activity of the rectus abdominis muscle was significantly delayed. This suggests that the time to peak activity of the anterior tibial muscle is shortened and the time of onset of activity of the rectus abdominis muscle is delayed in unexpected backward perturbation in patients with CVCF.

Sensory Re-Weighting in Human Bipedal Postural Control: The Effects of Experimentally-Induced Plantar Pain

The present study was designed to assess the effects of experimentally-induced plantar pain on the displacement of centre of foot pressure during unperturbed upright stance in different sensory conditions of availability and/or reliability of visual input and somatosensory input from the vestibular system and neck. To achieve this goal, fourteen young healthy adults were asked to stand as still as possible in three sensory conditions: (1) No-vision, (2) Vision, and (3) No-vision - Head tilted backward, during two experimental conditions: (1) a No-pain condition, and (2) a condition when a painful stimulation was applied to the plantar surfaces of both feet (Plantar-pain condition). Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed that (1) experimentally-induced plantar pain increased CoP displacements in the absence of vision (No-vision condition), (2) this deleterious effect was more accentuated when somatosensory information from the vestibular and neck was altered (No-vision - Head tilted backward condition) and (3) this deleterious effect was suppressed when visual information was available (Vision condition). From a fundamental point of view, these results lend support to the sensory re-weighting hypothesis whereby the central nervous system dynamically and selectively adjusts the relative contributions of sensory inputs (i.e. the sensory weightings) in order to maintain balance when one or more sensory channels are altered by the task (novel or challenging), environmental or individual conditions. From a clinical point of view, the present findings further suggest that prevention and treatment of plantar pain may be relevant for the preservation or improvement of balance control, particularly in situations (or individuals) in which information provided by the visual, neck proprioceptive and vestibular systems is unavailable or disrupted.

Stance- and Locomotion-Dependent Processing of Vibration-Induced Proprioceptive Inflow From Multiple Muscles in Humans

We performed a whole-body mapping study of the effect of unilateral muscle vibration, eliciting spindle Ia firing, on the control of standing and walking in humans. During quiet stance, vibration applied to various muscles of the trunk-neck system and of the lower limb elicited a significant tilt in whole body postural orientation. The direction of vibration-induced postural tilt was consistent with a response compensatory for the illusory lengthening of the stimulated muscles. During walking, trunk-neck muscle vibration induced ample deviations of the locomotor trajectory toward the side opposite to the stimulation site. In contrast, no significant modifications of the locomotor trajectory could be detected when vibrating various muscles of the lower as well as upper limb. The absence of correlation between the effects of muscle vibration during walking and standing dismisses the possibility that vibration-induced postural changes can account for the observed deviations of the locomotor trajectory during walking. We conclude that the dissimilar effects of trunk-neck and lower limb muscle vibration during walking and standing reflect a general sensory-motor plan, whereby muscle Ia input is processed according to both the performed task and the body segment from which the sensory inflow arises.

Craniocentric body-sway responses to 500 Hz bone-conducted tones in man

Whole-body responses evoked by bone-conducted sound, a stimulus known to activate vestibular afferents, were recorded in standing subjects deprived of vision. With the head facing forward, unilateral mastoid vibration (500 Hz, 2 s, 136 dB force level) produced an oblique body sway with a consistent lateral component away from the stimulated ear and an average forward component. The side of stimulation had a powerful influence on the direction but not the magnitude of sway. Individuals' mean response directions were significantly clustered between subjects, as well as within subjects for 12 of 16 subjects when tested on five occasions. Single trial analysis did not reveal any habituation of the response. To investigate whether muscle spindle activation might be responsible for the response, vibration was applied directly over posterior and anterior neck muscles and tendons. This generally produced responses that were smaller and with different direction characteristics than with mastoid vibration. In contrast, stimulation over the temporal fossa produced responses similar in magnitude and direction to mastoid stimulation. When the head was turned in yaw to face in different directions the sway response changed direction by the same amount but with no change in magnitude, suggesting response organization in a craniocentric reference frame. Whole-body sway evoked by 500 Hz vibration delivered over sites close to the ear is thus likely to represent a vestibular-evoked balance response. When compared with sway responses evoked by 500 Hz vibration of the left temporal fossa, responses to 1 mA left cathodal galvanic vestibular stimulation were of similar magnitude, yet significantly different in direction, suggesting differences in the end organ afferents activated by these two stimuli. This may enable investigation of previously inaccessible aspects of vestibular function in intact freely behaving human subjects.

Postural reactions to neck vibration in Parkinson's disease

To test the hypothesis that reduced reactions to proprioceptive input signals contribute to postural instability in Parkinson's disease (PD), pulses of mechanical vibration were applied to the neck muscles of PD patients and healthy controls. This stimulus elicits postural reactions in standing subjects. Participating were 13 moderately affected PD patients, 13 severely affected PD patients, and 13 age-matched healthy subjects. Patients were tested on and off medication. Three-second-long pulses of vibration were regularly (10 times) applied to the posterior neck muscles while subjects kept their eyes open or closed. Postural responses to the stimuli were measured by static posturography. No intergroup difference in the pattern and latencies of responses was found. However, the amplitudes of the postural reactions (shift of center of foot pressure) were significantly larger in advanced PD patients; those of moderately affected PD patients did not differ from those of control subjects. Moreover, the size of postural responses in both latter groups decreased across the trial contrary to that of advanced PD patients. Comparison of the measures during on and off testing revealed no significant differences. These results indicate that neither afferent proprioceptive deficits nor central integrative functions but rather scaling and habituation of erroneous proprioceptive information are disturbed in the postural control of advanced PD. Nondopaminergic structures seem to be responsible for this impairment.

Comparison of tap-evoked and tone-evoked postural reflexes in humans

To find an easy clinical test of postural reflexes, we compared tone and tap stimuli for eliciting postural reactions in leg muscles in 13 healthy subjects during upright stance. Tones (1000 Hz, 90 dB nHl) were presented monaurally via headphones; taps were applied with a reflex hammer to the forehead. Surface EMG was recorded from the medial gastrocnemius and the sternocleidomastoid muscles, and rectified and averaged. Tapping the forehead of a standing subject evoked leg muscle reflexes that began 50 ms after the stimulus in all subjects. Tone-evoked leg muscle reflexes behaved differently, i.e., they had smaller amplitudes and could be recorded in only 5 of 13 subjects. However, this same acoustic stimulus elicited reflex activity in the neck muscles of all subjects. There were also other differences (amplitudes, dependence on pre-activation) between these two reflexes. Tone-evoked leg muscle responses and tone-evoked neck muscle responses seem to be mediated by different structures, i.e., the latter by an oligosynaptic pathway and the former by polysynaptic neural circuits. We conclude that tap-evoked leg muscle responses are not or not solely mediated by saccular receptors but other receptors (i.e., proprioceptors, semicircular canals) are probably also involved.

Postural responses and spatial orientation to neck proprioceptive and vestibular inputs during locomotion in young and older adults

Both vestibular and neck proprioceptive inputs contribute towards maintaining a walking trajectory. We investigated how aging alters neck proprioceptive and vestibular interaction for preserving equilibrium and spatial orientation during locomotion. Young and healthy elderly were exposed to two sensory manipulations as they walked, eyes closed, to a target located straight ahead: (1) right side dorsal neck muscle vibration (Vib), and (2) Vib + transmastoidal galvanic vestibular stimulation (Vib + GVS). The maximum path deviation, average frontal centre of mass velocity and average trunk roll were evaluated. Trunk yaw rotation was computed at every metre of the path. We observed that directional responses to neck muscle stimulation were very sensitive to the reference frame generated by vestibular information. The attenuation of path deviation in older adults can be attributed to a reduced sensitivity of the neck proprioceptive system rather than the vestibular system.

Gait-dependent integration of neck muscle afferent input

We investigated the integration of neck muscle afferents during walking and running. Subjects walked or ran straight ahead, with or without an additional mass (20% of body weight). They performed all trials without vibration and with continuous vibration (80 Hz) applied to the lateral aspect of the neck. Vibration systematically caused body deviation toward the side opposite to the stimulation. The amplitude of vibration-induced body deviations was dramatically larger for walking (21.6 +/- 4.6 degrees ) than for running (8.0 +/- 2.5 degrees ). The additional mass marginally straightened body trajectory (average 5.6%), indicating that the gait-dependent effect of neck vibration cannot solely be attributed to differences in body inertia between walking and running. We concluded that neck muscle afferences are selectively gated according to the gait performed.

Vestibular actions on back and lower limb muscles during postural tasks in man

The vestibular system was activated by galvanic electrical stimulation in 19 normal subjects. With the head turned to one side so that the stimulating anode was on the posterior mastoid process, stimulation caused standing subjects to sway backwards in the sagittal plane. Electromyography showed bilateral activation of erector spinae, gluteus maximus, biceps femoris, soleus and intrinsic foot (toe flexor) muscles. When head direction or electrode polarity was reversed so that the anode was anterior, all those muscles became less active and the subjects swayed forwards. With the head facing forward, stimulation caused sideways sway in the coronal plane, towards the anode, with excitation of the erector spinae on the anode side and reduced activity on the cathode side. The limb muscles were activated on the side opposite the anode and showed complex responses on the anode side. Responses were detectable in the erectores spinae muscles in sitting subjects. No responses in limb muscles were detected in the sitting posture. Subject responses in erector spinae recorded at L3/L4 had latencies from 59 to 110 ms, using a 2 mA stimulus. Latencies in lower limb muscles were longer. The results suggest a role for the vestibular system and descending brain stem motor pathways to the erectores spinae muscles in the control of postural orientation of the back when sitting and standing. The conduction velocity in the motor pathway was estimated to be 13 +/- 10 m s(-1) (mean +/- S.D., n = 12 subjects).

Neck muscle vibration and spatial orientation during stepping in place in humans

Unilateral long-lasting vibration was applied to the sternomastoid muscle to assess the influence of asymmetric neck proprioceptive input on body orientation during stepping-in-place. Blindfolded subjects performed 3 sequences of 3 trials, each lasting 60 s: control, vibration applied during stepping (VDS), and vibration applied before stepping (VBS). VDS caused clear-cut whole body rotation toward the side opposite to vibration. The body rotated around a vertical axis placed at about arm's length from the body. The rotation did not begin immediately on switching on the vibrator. The delay varied from subject to subject from a few seconds to about 10 s. Once initiated, the angular velocity of rotation was remarkably constant (about 1 degrees /s). In VBS, at the beginning of stepping, subjects rotated for a while as if their neck were still vibrated. At a variable delay, the direction of rotation reversed, and the effects were opposite to those observed during VDS. Under no condition did head rotation, head roll, or lateral body tilt accompany rotation. The results confirm and extend the notion that the neck proprioceptive input plays a major role in body orientation during locomotion. The body rotation does not seem to depend on the same mechanisms that modify the erect posture; rather, the asymmetric neck input would seem to modify the egocentric body-centered coordinate system.