Soleus H-reflex and its relation to static postural control

High-Definition Trans-Spinal Current Stimulation Improves Balance and Somatosensory Control: A Randomised, Placebo-Controlled Trial

OBJECTIVES

To investigate and compare the effects of three different high-definition (HD) non-invasive current stimulation (NICS) protocols on the spinal cord on support balance and somatosensory abilities in healthy young people.

METHODS

Fifty-eight students were enrolled in this crossover study. All participants underwent application of (i) 1.5 mA anodal high-definition trans spinal direct current stimulation (HD-tsDCS), (ii) 1.5 mA cathodal HD-tsDCS, (iii) 1.5 mA high-definition trans spinal alternating current stimulation (HD-tsACS), and (iv) sham HD-tsDCS/ACS over the eighth thoracic vertebra in a randomised order. Balance (Y Balance test), deep sensitivity (Tuning Fork Test), and superficial sensitivity (Monofilament Test) of the lower limbs were tested immediately before and after each intervention.

RESULTS

Balance ability improved significantly following anodal HD-tsDCS and HD-tsACS compared with that following sham HD-tsDCS/ACS. Similarly, deep sensitivity increased significantly with anodal HD-tsDCS and HD-tsACS compared to that with sham HD-tsDCS/ACS and cathodal HD-tsDCS. Furthermore, superficial sensitivity improved significantly following anodal HD-tsDCS compared with that after HD-tsACS and cathodal HD-tsDCS.

CONCLUSIONS

Our data show that HD-tsNICS effectively modulates the balance and somatosensory control of the lower limbs. Several diseases are associated with illness-induced changes in the spinal network in parallel with sensorimotor disabilities. Non-invasive spinal modulation may be a favourable alternative to conventional brain applications in rehabilitation. Future studies should therefore investigate these promising approaches among cohorts of patients with disabilities.

Effects of cerebellar transcranial direct current stimulation on the excitability of spinal motor neurons and vestibulospinal tract in healthy individuals

Cerebellar transcranial direct current stimulation (ctDCS) modulates cerebellar cortical excitability in a polarity-dependent manner and affects inhibitory pathways from the cerebellum. The cerebellum modulates spinal reflex excitability via the vestibulospinal tract and other pathways projecting to the spinal motor neurons; however, the effects of ctDCS on the excitability of spinal motor neurons and vestibulospinal tract remain unclear. The experiment involved 13 healthy individuals. ctDCS (sham-ctDCS, anodal-ctDCS, and cathodal-ctDCS) was applied to the cerebellar vermis at 2 mA with an interval of at least 3 days between each condition. We measured the maximal M-wave (Mmax) and maximal H-reflex (Hmax) in the right soleus muscle to assess the excitability of spinal motor neurons. We applied galvanic vestibular stimulation (GVS) for 200 ms at 100 ms before tibial nerve stimulation to measure Hmax conditioned by GVS (GVS-Hmax) and calculated the change rate of Hmax by GVS as the excitability of vestibulospinal tract. We measured the Mmax, Hmax, and GVS-Hmax before, during, and after ctDCS in the sitting posture. No main effects of tDCS condition, main effects of time, or interaction effects were observed in Hmax/Mmax or the change rate of Hmax by GVS. It has been suggested that ctDCS does not affect the excitability of spinal motor neurons and vestibulospinal tract, as measured by neurophysiological methods, such as the H-reflex, in healthy individuals in a sitting posture. Effect of ctDCS on other descending pathways to spinal motor neurons, the neurological mechanism of tDCS and the cerebellar activity during the experiment may have contributed to these results. Therefore, we need to investigate the involvement of the cerebellum in Hmax/Mmax and the change rate of Hmax by GVS under different neuromodulation techniques and postural conditions.

Influence of oral motor tasks on postural muscle activity during dynamic reactive balance

BACKGROUND

Jaw clenching improves dynamic reactive balance on an oscillating platform during forward acceleration and is associated with decreased mean sway speed of different body regions.

OBJECTIVE

It is suggested that jaw clenching as a concurrent muscle activity facilitates human motor excitability, increasing the neural drive to distal muscles. The underlying mechanism behind this phenomenon was studied based on leg and trunk muscle activity (iEMG) and co-contraction ratio (CCR).

METHODS

Forty-eight physically active and healthy adults were assigned to three groups, performing three oral motor tasks (jaw clenching, tongue pressing against the palate or habitual lower jaw position) during a dynamic one-legged stance reactive balance task on an oscillating platform. The iEMG and CCR of posture-relevant muscles and muscle pairs were analysed during platform forward acceleration.

RESULTS

Tongue pressing caused an adjustment of co-contraction patterns of distal muscle groups based on changes in biomechanical coupling between the head and trunk during static balancing at the beginning of the experiment. Neither iEMG nor CCR measurement helped detect a general neuromuscular effect of jaw clenching on the dynamic reactive balance.

CONCLUSION

The findings might indicate the existence of robust fixed patterns of rapid postural responses during the important initial phases of balance recovery.

Physical Therapy Intervention Effects on Alteration of Spinal Excitability in Patients With Chronic Ankle Instability: A Systematic Review and Meta-analysis

CONTEXT

Chronic ankle instability (CAI) is a common injury in athletes. Different forms of physical therapy have been applied to the population with CAI to assess their impact on spinal excitability.

OBJECTIVE

The purpose of this systematic review and meta-analysis was to investigate the effectiveness of various physical therapy interventions on the alteration of spinal excitability in patients with CAI.

DATA SOURCES

Four databases (EMBASE, MEDLINE, Cochrane CENTRAL, and Scopus) were searched from inception to November 2022.

STUDY SELECTION

A total of 253 studies were obtained and screened; 11 studies on the effects of physical therapy intervention on the alteration of spinal excitability in patients with CAI were identified for meta-analysis.

STUDY DESIGN

Systematic review and meta-analysis.

LEVEL OF EVIDENCE

Level 3a.

DATA EXTRACTION

A total of 11 studies that included the maximal Hoffmann reflex normalized by the maximal muscle response (H/M ratio) in the peroneus longus and soleus muscles were extracted and summarized. The quality of the studies was assessed using the PEDro scale.

RESULTS

The extracted studies had an average PEDro score of 4.7 ± 1.4, indicating that most of them had fair-to-good quality. The physical therapy interventions included cryotherapy, taping, mobilization, proprioceptive training, and dry needling. The overall effects showed that the H/M ratios of the peroneus longus (P = 0.44, I2 = 0%) and soleus (P = 0.56,I2 = 22%) muscles were not changed by physical therapy in patients with CAI.

CONCLUSION

The meta-analysis indicated that physical therapy interventions such as cryotherapy, taping, mobilization, proprioceptive training, and dry needling do not alter the spinal excitability in patients with CAI. Given that only 1 study reported ineffective changes in spinal excitability with dry needling, more research is essential to establish and validate its efficacy.

PROSPERO REGISTRATION

CRD42022372998.

Direct Current Stimulation over the Primary Motor Cortex, Cerebellum, and Spinal Cord to Modulate Balance Performance: A Randomized Placebo-Controlled Trial

OBJECTIVES

Existing applications of non-invasive brain stimulation in the modulation of balance ability are focused on the primary motor cortex (M1). It is conceivable that other brain and spinal cord areas may be comparable or more promising targets in this regard. This study compares transcranial direct current stimulation (tDCS) over (i) the M1, (ii) the cerebellum, and (iii) trans-spinal direct current stimulation (tsDCS) in the modulation of balance ability.

METHODS

Forty-two sports students were randomized in this placebo-controlled study. Twenty minutes of anodal 1.5 mA t/tsDCS over (i) the M1, (ii) the cerebellum, and (iii) the spinal cord, as well as (iv) sham tDCS were applied to each subject. The Y Balance Test, Single Leg Landing Test, and Single Leg Squat Test were performed prior to and after each intervention.

RESULTS

The Y Balance Test showed significant improvement after real stimulation of each region compared to sham stimulation. While tsDCS supported the balance ability of both legs, M1 and cerebellar tDCS supported right leg stand only. No significant differences were found in the Single Leg Landing Test and the Single Leg Squat Test.

CONCLUSIONS

Our data encourage the application of DCS over the cerebellum and spinal cord (in addition to the M1 region) in supporting balance control. Future research should investigate and compare the effects of different stimulation protocols (anodal or cathodal direct current stimulation (DCS), alternating current stimulation (ACS), high-definition DCS/ACS, closed-loop ACS) over these regions in healthy people and examine the potential of these approaches in the neurorehabilitation.

Neural Correlates of Balance Skill Learning in Young and Older Individuals: A Systematic Review and Meta-analysis

BACKGROUND

Despite the increasing number of research studies examining the effects of age on the control of posture, the number of annual fall-related injuries and deaths continues to increase. A better understanding of how old age affects the neural mechanisms of postural control and how countermeasures such as balance training could improve the neural control of posture to reduce falls in older individuals is therefore necessary. The aim of this review is to determine the effects of age on the neural correlates of balance skill learning measured during static (standing) and dynamic (walking) balance tasks in healthy individuals.

METHODS

We determined the effects of acute (1-3 sessions) and chronic (> 3 sessions) balance skill training on balance in the trained and in untrained, transfer balance tasks through a systematic review and quantified these effects by robust variance estimation meta-analysis in combination with meta-regression. We systematically searched PubMed, Web of Science, and Cochrane databases. Balance performance and neural plasticity outcomes were extracted and included in the systematic synthesis and meta-analysis.

RESULTS

Forty-two studies (n = 622 young, n = 699 older individuals) were included in the systematic synthesis. Seventeen studies with 508 in-analysis participants were eligible for a meta-analysis. The overall analysis revealed that acute and chronic balance training had a large effect on the neural correlates of balance skill learning in the two age groups combined (g = 0.79, p < 0.01). Both age groups similarly improved balance skill performance in 1-3 training sessions and showed little further improvements with additional sessions. Improvements in balance performance mainly occurred in the trained and less so in the non-trained (i.e., transfer) balance tasks. The systematic synthesis and meta-analysis suggested little correspondence between improved balance skills and changes in spinal, cortical, and corticospinal excitability measures in the two age groups and between the time courses of changes in balance skills and neural correlates.

CONCLUSIONS

Balance skill learning and the accompanying neural adaptations occur rapidly and independently of age with little to no training dose-dependence or correspondence between behavioral and neural adaptations. Of the five types of neural correlates examined, changes in only spinal excitability seemed to differ between age groups. However, age or training dose in terms of duration did not moderate the effects of balance training on the changes in any of the neural correlates. The behavioral and neural mechanisms of strong task-specificity and the time course of skill retention remain unclear and require further studies in young and older individuals.

REGISTRATION

PROSPERO registration number: CRD42022349573.

The stepping test, and infrared depth sensor, provide reliable measures of balance in community-dwelling older adults

[Purpose] The purpose was to examine relationships between variables characterizing the 20-second stepping test movement pattern, assessed with an infrared depth sensor (KinectTM), and measurements of dynamic and static balance. [Participants and Methods] A total of 27 independent-living, older adults (7 males and 20 females) participated in this study. For each participant, the stepping test total movement distance, movement displacement, knee movement distance, and step number were calculated from Kinect closed joint-point coordinate data. Dynamic and static balance were assessed using a NeuroCom Balance Master Platform system. [Results] The stepping test total movement distance had a moderate negative correlation with endpoint excursion (r=-0.469) and a moderate positive correlation with total movement distance, corrected for knee movement distance (r=0.557). Step numbers had a moderate negative correlation with stepping test total movement distance (r=-0.667) and total movement distance, corrected for knee movement distance (r=-0.531). Division into high and low-balance sub-groups (based on endpoint excursion or sway velocity scores) revealed that stepping test total movement distances and movement displacements were greater, and step numbers were fewer, in low balance groups. [Conclusion] The stepping test, combined with a KinectTM-assessed movement pattern provides a simple, objective, reliable means for assessing balance in community-dwelling, independent-living older adults.

Heating the skin on the foot sole enhances cutaneous reflexes in the lower limb

Cutaneous input is important in postural control and balance. Aging and diabetes impair skin sensitivity and motor control. Heat application can improve skin sensation, but its influence on motor control remains unknown. This study investigated the effects of heating the skin of the foot sole on lower limb cutaneous reflexes. Reflexes were evoked in the tibialis anterior muscle of 20 young, healthy adults before and after heating the foot sole to a maximum of 42°C. While holding a 15% maximum root mean square EMG generated during maximum isometric dorsiflexion, a filtered white noise (0-50 Hz) vibration at 10 times the perceptual threshold was applied to the heel to stimulate cutaneous mechanoreceptors. Reflexes were analyzed in both the time (cumulant density) and frequency (coherence, gain) domains. Heat increased foot skin temperature ∼15.4°C (P < 0.001). Cumulant density peak to peak amplitude significantly increased by 44% after heating (P = 0.01) while latencies did not vary (P = 0.46). Coherence and gain were significantly greater in the 30- to 40-Hz range following heating (P = 0.048; P = 0.02). Heating significantly enhances lower limb cutaneous reflexes. This may be due to the increased ability of cutaneous mechanoreceptors to encode in the 30- to 40-Hz range.NEW & NOTEWORTHY Cutaneous input is a known modulator of muscle activity. Targeting skin to intentionally enhance motor output has received little attention. We explored local skin heating to enhance skin sensitivity and found a significant increase in the amplitude, coherence, and gain of cutaneous reflexes in the tibialis anterior. Our current findings provide the first support for the use of heat as a viable and easily integrated modality in rehabilitation technology to improve balance and postural control.

Sex differences concerning the effects of ankle muscle fatigue on static postural control and spinal proprioceptive input at the ankle

Aims

The main aim of this study was to determine sex differences in postural control changes with ankle muscle fatigue during a standing forward leaning (FL) task under different vision conditions. The secondary aim was to examine sex differences in the effect of fatigue on soleus (SOL) H-reflex amplitude, a measure of motoneuron excitability with activation of Ia afferents.

Methods

Fifteen healthy young adult males (mean age: 28.0 years) and 16 healthy young adult females (mean age: 26.1 years) were asked to perform four consecutive FL tasks [30 s; two with eyes open (EO) and two with eyes closed (EC)] before, and immediately following a fatiguing exercise consisting of alternating ankle plantarflexion (6 s) and dorsiflexion (2 s) maximal isometric contractions, and at 5 and 10 min of recovery. Center of pressure (COP) sway variables (mean position, standard deviation, ellipse area, average velocity, and frequency), an ankle co-contraction index, and a ratio of SOL H-reflex to the maximum amplitude of the compound muscle action potential (M-max) were obtained during the FL tasks. A rating of perceived fatigue (RPF) was also documented at the different time points.

Results

Time to task failure (reduction of 50% in maximal voluntary isometric contraction torque of ankle plantar flexors) and the increase in RPF value were not significantly different between males and females. Both sex groups showed similar and significant increases (p < 0.05) in mean COP sway velocity with no significant changes in co-contraction indices. No significant effects of fatigue and related interactions were found for SOL H/M-max ratio.

Discussion

The absence of a significant sex difference in postural control change (sway and co-contraction) with fatigue could be explained by similar perceived (RPF) and performance fatigability (exercise duration) between males and females in the present study. Fatigue did not lead to significant changes in SOL spinal motoneuron excitability with activation of Ia afferents.

Effects of a short period of postural training on postural stability and vestibulospinal reflexes

The effects of postural training on postural stability and vestibulospinal reflexes (VSRs) were investigated in normal subjects. A period (23 minutes) of repeated episodes (n = 10, 50 seconds) of unipedal stance elicited a progressive reduction of the area covered by centre of pressure (CoP) displacement, of average CoP displacement along the X and Y axes and of CoP velocity observed in this challenging postural task. All these changes were correlated to each other with the only exception of those in X and Y CoP displacement. Moreover, they were larger in the subjects showing higher initial instability in unipedal stance, suggesting that they were triggered by the modulation of sensory afferents signalling body sway. No changes in bipedal stance occurred soon and 1 hour after this period of postural training, while a reduction of CoP displacement was apparent after 24 hours, possibly due to a beneficial effect of overnight sleep on postural learning. The same period of postural training also reduced the CoP displacement elicited by electrical vestibular stimulation (EVS) along the X axis up to 24 hours following the training end. No significant changes in postural parameters of bipedal stance and VSRs could be observed in control experiments where subjects were tested at identical time points without performing the postural training. Therefore, postural training led to a stricter control of CoP displacement, possibly acting through the cerebellum by enhancing feedforward mechanisms of postural stability and by depressing the VSR, the most important reflex mechanism involved in balance maintenance under challenging conditions.

Priming locomotor training with transspinal stimulation in people with spinal cord injury: study protocol of a randomized clinical trial

BACKGROUND

The seemingly simple tasks of standing and walking require continuous integration of complex spinal reflex circuits between descending motor commands and ascending sensory inputs. Spinal cord injury greatly impairs standing and walking ability, but both improve with locomotor training. However, even after multiple locomotor training sessions, abnormal muscle activity and coordination persist. Thus, locomotor training alone cannot fully optimize the neuronal plasticity required to strengthen the synapses connecting the brain, spinal cord, and local circuits and potentiate neuronal activity based on need. Transcutaneous spinal cord (transspinal) stimulation alters motoneuron excitability over multiple segments by bringing motoneurons closer to threshold, a prerequisite for effectively promoting spinal locomotor network neuromodulation and strengthening neural connectivity of the injured human spinal cord. Importantly, whether concurrent treatment with transspinal stimulation and locomotor training maximizes motor recovery after spinal cord injury is unknown.

METHODS

Forty-five individuals with chronic spinal cord injury are receiving 40 sessions of robotic gait training primed with 30 Hz transspinal stimulation at the Thoracic 10 vertebral level. Participants are randomized to receive 30 min of active or sham transspinal stimulation during standing or active transspinal stimulation while supine followed by 30 min of robotic gait training. Over the course of locomotor training, the body weight support, treadmill speed, and leg guidance force are adjusted as needed for each participant based on absence of knee buckling during the stance phase and toe dragging during the swing phase. At baseline and after completion of all therapeutic sessions, neurophysiological recordings registering corticospinal and spinal neural excitability changes along with clinical assessment measures of standing and walking, and autonomic function via questionnaires regarding bowel, bladder, and sexual function are taken.

DISCUSSION

The results of this mechanistic randomized clinical trial will demonstrate that tonic transspinal stimulation strengthens corticomotoneuronal connectivity and dynamic neuromodulation through posture-dependent corticospinal and spinal neuroplasticity. We anticipate that this mechanistic clinical trial will greatly impact clinical practice because, in real-world clinical settings, noninvasive transspinal stimulation can be more easily and widely implemented than invasive epidural stimulation. Additionally, by applying multiple interventions to accelerate motor recovery, we are employing a treatment regimen that reflects a true clinical approach.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04807764 . Registered on March 19, 2021.

Protocols Targeting Afferent Pathways via Neuromuscular Electrical Stimulation for the Plantar Flexors: A Systematic Review

This systematic review documents the protocol characteristics of studies that used neuromuscular electrical stimulation protocols (NMES) on the plantar flexors [through triceps surae (TS) or tibial nerve (TN) stimulation] to stimulate afferent pathways. The review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement, was registered to PROSPERO (ID: CRD42022345194) and was funded by the Greek General Secretariat for Research and Technology (ERA-NET NEURON JTC 2020). Included were original research articles on healthy adults, with NMES interventions applied on TN or TS or both. Four databases (Cochrane Library, PubMed, Scopus, and Web of Science) were systematically searched, in addition to a manual search using the citations of included studies. Quality assessment was conducted on 32 eligible studies by estimating the risk of bias with the checklist of the Effective Public Health Practice Project Quality Assessment Tool. Eighty-seven protocols were analyzed, with descriptive statistics. Compared to TS, TN stimulation has been reported in a wider range of frequencies (5-100, vs. 20-200 Hz) and normalization methods for the contraction intensity. The pulse duration ranged from 0.2 to 1 ms for both TS and TN protocols. It is concluded that with increasing popularity of NMES protocols in intervention and rehabilitation, future studies may use a wider range of stimulation attributes, to stimulate motor neurons via afferent pathways, but, on the other hand, additional studies may explore new protocols, targeting for more optimal effectiveness. Furthermore, future studies should consider methodological issues, such as stimulation efficacy (e.g., positioning over the motor point) and reporting of level of discomfort during the application of NMES protocols to reduce the inherent variability of the results.

Priming locomotor training with transspinal stimulation in people with spinal cord injury: study protocol of a randomized clinical trial

Background

The seemingly simple tasks of standing and walking require continuous integration of complex spinal reflex circuits between descending motor commands and ascending sensory inputs. Spinal cord injury greatly impairs standing and walking ability, but both improve with locomotor training. However, even after multiple locomotor training sessions, abnormal muscle activity and coordination persist. Thus, locomotor training alone cannot fully optimize the neuronal plasticity required to strengthen the synapses connecting the brain, spinal cord, and local circuits and potentiate neuronal activity based on need. Transcutaneous spinal cord (transspinal) stimulation alters motoneuron excitability over multiple segments by bringing motoneurons closer to threshold, a prerequisite for effectively promoting spinal locomotor network neuromodulation and strengthening neural connectivity of the injured human spinal cord. Importantly, whether concurrent treatment with transspinal stimulation and locomotor training maximizes motor recovery after spinal cord injury is unknown.

Methods

Forty-five individuals with chronic spinal cord injury are receiving 40 sessions of robotic gait training primed with 30 Hz transspinal stimulation at the Thoracic 10 vertebral level. Participants are randomized to receive 30-minutes of active or sham transspinal stimulation during standing or active transspinal stimulation while supine followed by 30-minutes of robotic gait training. Over the course of locomotor training, the body weight support, treadmill speed, and leg guidance force are adjusted as needed for each participant based on absence of knee buckling during the stance phase and toe dragging during the swing phase. At baseline and after completion of all therapeutic sessions, neurophysiological recordings registering corticospinal and spinal neural excitability changes along with clinical assessment measures of standing and walking, and autonomic function via questionnaires regarding bowel, bladder and sexual function are taken.

Discussion

The results of this mechanistic randomized clinical trial will demonstrate that tonic transspinal stimulation strengthens corticomotoneuronal connectivity and dynamic neuromodulation through posture-dependent corticospinal and spinal neuroplasticity. We anticipate that this mechanistic clinical trial will greatly impact clinical practice because in real-world clinical settings, noninvasive transspinal stimulation can be more easily and widely implemented than invasive epidural stimulation. Additionally, by applying multiple interventions to accelerate motor recovery, we are employing a treatment regimen that reflects a true clinical approach.

Trial registration

ClinicalTrials.gov: NCT04807764; Registered on March 19, 2021.

Comparison of the soleus and plantaris muscles in humans and other primates: Macroscopic neuromuscular anatomy and evolutionary significance

In humans, the soleus is more developed compared to other primates and has a unique architecture composed of anterior bipennate and posterior unipennate parts, which are innervated by different nerve branches. The anterior part of the human soleus was proposed to be important for bipedalism, however, the phylogenetic process resulting in its acquisition remains unclear. Providing insights into this process, the anterior part of the soleus was suggested to be closely related to the plantaris based on the branching pattern of their nerve fascicles. To reveal the phylogeny of the soleus and plantaris in primates, the innervation patterns of the posterior crural muscles were compared among a wide range of species. From their branching pattern, posterior crural muscles could be classified into superficial and deep muscle groups. The anterior part of the soleus and plantaris both belonged to the deep muscle group. In all the examined specimens of ring-tailed lemurs and chimpanzees, as well as in one out of two specimens of siamang, the nerve branches corresponding to those innervating the anterior part of the human soleus were found. The muscular branches innervating the anterior part of the soleus and plantaris formed a common trunk or were connected in all the specimens. These results indicate that the anterior part of the soleus is closely related to the plantaris across different species of primates. In turn, this suggests that the anterior part of the soleus is maintained among primates, and especially in humans, where it develops as the characteristic bipennate structure.

The effect of loss of foot sole sensitivity on H-reflex of triceps surae muscles and functional gait

Objective: To investigate the effects of foot sole insensitivity on the outcomes of the triceps surae muscle H-reflex and functional gait. Material and Methods: People with peripheral neuropathy were recruited and divided into two groups: people with more (n = 13, 73.3 ± 4.3 years old) or less (n = 10, 73.5 ± 5.3) sensitive tactile sensation. Their monofilament testing scores were 9.0 ± 1.5 (range: 7-10) and 2.3 ± 2.4 (range: 0-6) out of 10, respectively. H-reflex of the triceps surae muscles during quiet standing and their relationship with functional gait, 6 min walking distance (6MWD), and timed-up-and-go duration (TUG), were compared between groups. Results: No significant difference was detected for H-reflex parameters between the groups. The less sensitive group showed reduced (p < .05) functional gait capacity compared to the other group, 38.4 ± 52.7 vs. 463.5 ± 47.6 m for 6MWD, and 9.0 ± 1.5 vs. 7.2 ± 1.1s for TUG, respectively. A significant correlation (p < .05), worse functional gait related to greater H/M ratio, was observed in the less sensitive group, not the other group. Conclusion: Although there was no significant H-reflex difference between the groups, more pronounced tactile sensation degeneration affected functional gaits and their relationship with H-reflex.

The Impact of Hoffmann Reflex on Standing Postural Control Complexity in the Elderly with Impaired Plantar Sensation

In people with peripheral neuropathy (PN), impaired plantar sensation can cause adaptive changes in the central nervous system (CNS), resulting in changes in the standing postural control, which is reflected in the variability of standing output signals. Standard deviation (SD) and entropy are reliable indicators of system variability, especially since entropy is highly sensitive to diseased populations. The relation between SD and entropy, CNS and center of pressure (COP) variability is unclear for people with severe PN. The purpose of this study was to explore the adaptability of the CNS to the severe of PN and its effect on the degree and complexity of COP variability. Here, people with PN were divided into less affected (LA) and more affected (MA) groups based on plantar pressure sensitivity. We studied Hoffmann reflex (H-reflex) and standing balance performance with the control group (n = 8), LA group (n = 10), and MA group (n = 9), recording a 30 s COP time series (30,000 samples) of double-leg standing with eyes open. We observed that the more affected group had less COP complexity than people without PN. There is a significant negative correlation between the SD and sample entropy in people without PN, less affected and more affected. The COP complexity in people without PN was inversely correlated with H-reflex. We concluded that: (1) The complexity of COP variability in patients with severe plantar sensory impairment is changed, which will not affect the degree of COP variability; (2) The independence of the COP entropy in the AP and ML directions decreased, and the interdependence increased in people with PN; (3) Although the CNS of people with PN has a greater contribution to standing balance, its modulation of standing postural control is decreased.

Non-invasive brain stimulation for improving gait, balance, and lower limbs motor function in stroke

Objectives

This systematic review and meta-analysis aim to summarize and analyze the available evidence of non-invasive brain stimulation/spinal cord stimulation on gait, balance and/or lower limb motor recovery in stroke patients.

Methods

The PubMed database was searched from its inception through to 31/03/2021 for randomized controlled trials investigating repetitive transcranial magnetic stimulation or transcranial/trans-spinal direct current/alternating current stimulation for improving gait, balance and/or lower limb motor function in stroke patients.

Results

Overall, 25 appropriate studies (including 657 stroke subjects) were found. The data indicates that non-invasive brain stimulation/spinal cord stimulation is effective in supporting recovery. However, the effects are inhomogeneous across studies: (1) transcranial/trans-spinal direct current/alternating current stimulation induce greater effects than repetitive transcranial magnetic stimulation, and (2) bilateral application of non-invasive brain stimulation is superior to unilateral stimulation.

Conclusions

The current evidence encourages further research and suggests that more individualized approaches are necessary for increasing effect sizes in stroke patients.

Soleus H-reflex modulation in cerebral palsy and its relationship with neural control complexity: a pilot study

Individuals with cerebral palsy (CP) display motor control patterns that suggest decreased supraspinal input, but it remains unknown if they are able to modulate lower-limb reflexes in response to more complex tasks, or whether global motor control patterns relate to reflex modulation capacity in this population. Eight ambulatory individuals with CP (12-18 years old) were recruited to complete a task complexity protocol, where soleus H-reflex excitability was compared between bilateral (baseline) and unilateral (complex) standing. We also investigated the relationship between each participant's ability to modulate soleus H-reflex excitability and the complexity of their walking neural control pattern determined from muscle synergy analysis. Finally, six of the eight participants completed an exoskeleton walking protocol, where soleus H-reflexes were collected during the stance phase of walking with and without stance-phase plantar flexor resistance. Participants displayed a significant reduction in soleus H-reflex excitability (- 26 ± 25%, p = 0.04) with unilateral standing, and a strong positive relationship was observed between more refined neural control during walking and an increased ability to modulate reflex excitability (R = 0.79, p = 0.04). There was no difference in neuromuscular outcome measures with and without the ankle exoskeleton (p values all > 0.05), with variable reflex responses to walking with ankle exoskeleton resistance. These findings provide evidence that ambulatory individuals with CP retain some capacity to modulate lower-limb reflexes in response to increased task complexity, and that less refined neural control during walking appears to be related to deficits in reflex modulation.

The Reduced Adaptability of H-Reflex Parameters to Postural Change With Deficiency of Foot Plantar Sensitivity

Purpose: The project was to examine the influence of peripheral neuropathy (PN) severity on the relationship between Hoffmann-reflex (H-reflex) and postures.

Methods: A total of 34 participants were recruited. H-reflex (H/M ratio and H-index) during prone, standing, and the heel-contact phase of walking was tested, along with foot sole sensitivity.

Results: The participants were divided into three groups based on the severity of the foot sole sensitivity deficit: control, less (LA), and more (MA) affected with both feet 5.07 monofilament test scores ranging 10, 0–5, and 6–9, respectively. A significant group by the posture interaction was observed in the H/M ratio (F_{3.0, 41.9} = 2.904, p = 0.046, η_p² = 0.172). In the control group, the H/M ratio of prone (22 ± 7%) was greater than that of the standing (13 ± 3%, p = 0.013) and heel-contact phase (10 ± 2%, p = 0.004). In the MA group, the H/M ratio of standing (13 ± 3%) was greater than that of the heel-contact phase (8 ± 2%, p = 0.011). The H-index was significantly different among groups (F_2,28 = 5.711, p = 0.008, and η_p²= 0.290). Post hoc analysis showed that the H-index of the control group (80.6 ± 11.3) was greater than that of the LA (69.8 ± 12.1, p = 0.021) and MA groups (62.0 ± 10.6, p = 0.003).

Conclusion: In a non-PN population, the plantar sensory input plays an important role in maintaining standing postural control, while as for the PN population with foot sole sensitivity deficiency, type Ⅰ afferent fibers reflex loop (H-reflex) contributes more to the standing postural control. The H-index parameter is an excellent method to recognize the people with and without PN but not to distinguish the severity of PN with impaired foot sole sensitivity.

Effects of H-Reflex Onset Latency on Gait in Elderly and Hemiplegic Individuals

Background and Objectives: The Hoffmann’s reflex (H-reflex) is important in electrodiagnostic testing because it improves sensitivity and specificity in diagnosing radiculopathies. Although quantitative electromyography (EMG) measurements for H-reflex amplitudes during the gait cycle have been performed in both hemiplegic and healthy individuals, research on the H-wave latency in these individuals during the gait cycle is lacking. Materials and Methods: The H-reflex latency of the soleus muscle was investigated in hemiplegic stroke patients and healthy elderly persons in this observational analytical study. Two groups of individuals participated in this study: healthy adults (n = 25) and stroke patients with hemiplegia (n = 25) were compared. An MP150 with Ag-Ag/Cl electrodes was utilized to record and analyse electromyography measurements. All individuals could walk independently indoors. Stimuli were administered to elicit the H-reflex in the four gait phases as the participant walked. Results: Stroke patients had a significantly shorter latency than did healthy patients in the mid-swing, mid-stance, and toe-off phases of the gait cycle; heel-strike latency did not significantly differ. Conclusions: These results can be used as diagnostic data to help account for patient characteristics or measure the recovery extent for treatment planning and gait training in hemiplegic individuals.

Transcutaneous spinal direct current stimulation (tsDCS) does not affect postural sway of young and healthy subjects during quiet upright standing

Transcutaneous spinal direct current stimulation (tsDCS) is an effective non-invasive spinal cord electrical stimulation technique to induce neuromodulation of local and distal neural circuits of the central nervous system (CNS). Applied to the spinal cord lumbosacral region, tsDCS changes electrophysiological responses of the motor, proprioceptive and nociceptive pathways, alters the performance of some lower limb motor tasks and can even modulate the behavior of supramedullary neuronal networks. In this study an experimental protocol was conducted to verify if tsDCS (5 mA, 20 minutes) of two different polarizations, applied over the lumbosacral region (tenth thoracic vertebrae (T10)), can induce changes in postural sway oscillations of young healthy individuals during quiet standing. A novel initialization of the electrical stimulation was developed to improve subject blinding to the different stimulus conditions including the sham trials. Measures of postural sway, both global and structural, were computed before, during and following the DC stimulation period. The results indicated that, for the adopted conditions, tsDCS did not induce statistically significant changes in postural sway of young healthy individuals during quiet standing.

The Effects of Intermittent Trunk Flexion With and Without Support on Sitting Balance in Young Adults

Prolonged trunk flexion is known to affect passive and active stabilization of the trunk. Previous studies have evaluated changes in spinal range of motion, muscle activity and reflex behavior induced by prolonged trunk flexion, whereas the effect on sitting postural control is vastly underexplored. In this study, we compared the effects of supported and unsupported intermittent trunk flexion on center of pressure (CoP) motion during sitting on an unstable seat. Participants (n = 21; 11 males, 23.2 ± 2.0 years; 10 females, age 24.3 ± 4.0) were exposed to 1-h intermittent (60-s sets with 30 s of rest) trunk flexion (80% of the maximal range of motion) and CoP root mean square distance, velocity and frequency before and after the exposure were assessed. Contrary to our hypothesis, there were no main effects of exposure (pre. vs. post flexion protocol; p = 0.128–0.709), no main effects of condition (supported vs. unsupported; p = 0.134–0.931), and no interaction between exposure and condition (p = 0.163–0.912). Our results indicate that prolonged intermittent flexion does not induce any changes in CoP motion during a seated balance task, regardless of the presence of a trunk support during prolonged intermittent flexion. This suggests a successful compensation of decreased passive stiffness by increased reflex activity.

Hoffmann Reflex Measured From Lateral Gastrocnemius Is More Reliable Than From Soleus Among Elderly With Peripheral Neuropathy

Introduction

Peripheral neuropathy (PN) affects up to 20% of the population over the age of 60. Hoffmann reflex (H-reflex) may assess PN adaptation by measuring the function of the peripheral neural system and central nervous system (CNS) modulation. This project aimed to find a reliable muscle among triceps surae muscles during standing and walking among the PN population.

Materials and Methods

Sixteen older adults (> 65 years of age) diagnosed with PN were recruited in this study. The H-reflex test was conducted on the muscle belly of the soleus (SOL), the medial (MG), and lateral gastrocnemius (LG) during standing and walking (heel contact, midstance, and toe-off phases). All measurements were collected on two occasions, separated by at least 7 days. Intraclass correlation coefficients (ICCs) and their confidence intervals (CIs) were used to examine the consistency of the H-reflex outcome variables in the repeated tests for all three tested muscles.

Results

The ICCs of H-index during standing and the three walking phases were poor to moderate in SOL (0.486∼0.737) and MG (0.221∼0.768), and moderate to high in LG (0.713∼0.871). The ICCs of H/M ratio were poor to moderate in SOL (0.263∼0.702) and MG (0.220∼0.733), and high in LG (0.856∼0.958).

Conclusion

The H-reflex of LG was more reliable than SOL and MG during standing and walking among older adults with peripheral neuropathy. It is crucial for future studies in this population to study H-reflex of LG, not SOL and MG, for more reliable results.

Acute effects of ankle plantar flexor force-matching exercises on postural strategy during single leg standing in healthy adults

BACKGROUND

Ankle plantar flexor force steadiness, assessed by measuring the fluctuation of the force around the submaximal target torque, has been associated with postural stability.

RESEARCH QUESTION

To investigate whether a force-matching exercise, where submaximal steady torque is maintained at the target torque, can modulate postural strategy immediately.

METHODS

Twenty-eight healthy young adults performed ankle plantar flexor force-matching exercises at target torques of 5%, 20%, and 50% of maximum voluntary contraction (MVC), in a randomized crossover trial. Participants with their ankle in a neutral position were instructed to maintain isometric contraction at each target torque, as measured by a dynamometer, for 20 s with 3 sets of 5 contractions. Before and after the force-matching exercises, the anterior-posterior velocities and standard deviation of the center of pressure (COP) on the stable platform and the tilt angle of the unstable platform during 20-seconds single-leg standing were measured. The velocities and standard deviations of the COP and tilt angle before and after the exercises were compared using paired t-tests.

RESULTS

The tilt angle velocity of an unstable platform significantly decreased after the force-matching exercise at a target torque of 5% MVC (p = 0.029), whereas it was unchanged after the exercises at target torques of 20% and 50% MVC. The standard deviations of the tilt angle of unstable platform test did not change significantly after any exercise. Furthermore, no significant differences were observed in the COP velocities or standard deviations on the stable platform test after any exercise.

SIGNIFICANCE

Our findings suggest that repeated exertion training at low-intensity contractions can affect postural stability in an unstable condition. Particularly, force-matching exercise at very low-intensity torque, such as 5% of MVC, may be an effective method to improve postural control in the unstable condition, but not in a stable condition.

An overview of the effects of whole-body vibration on individuals with cerebral palsy

The purpose of this review is to examine how whole-body vibration can be used as a tool in therapy to help improve common physical weaknesses in balance, bone density, gait, spasticity, and strength experienced by individuals with cerebral palsy. Cerebral palsy is the most common movement disorder in children, and whole-body vibration is quickly becoming a potential therapeutic tool with some advantages compared to traditional therapies for individuals with movement disorders. The advantages of whole-body vibration include less strain and risk of injury, more passive training activity, and reduced time to complete an effective therapeutic session, all of which are appealing for populations with physiological impairments that cause physical weakness, including individuals with cerebral palsy. This review involves a brief overview of cerebral palsy, whole-body vibration's influence on physical performance measures, its influence on physical performance in individuals with cerebral palsy, and then discusses the future directions of whole-body vibration therapy in the cerebral palsy population.

Soleus H-Reflex Change in Poststroke Spasticity: Modulation due to Body Position

Purpose

This study is aimed at exploring how soleus H-reflex change in poststroke patients with spasticity influenced by body position.

Materials and Methods

Twenty-four stroke patients with spastic hemiplegia and twelve age-matched healthy controls were investigated. Maximal Hoffmann-reflex (Hmax) and motor potential (Mmax) were elicited at the popliteal fossa in both prone and standing positions, respectively, and the Hmax/Mmax ratio at each body position was determined. Compare changes in reflex behavior in both spastic and contralateral muscles of stroke survivors in prone and standing positions, and match healthy subjects in the same position.

Results

In healthy subjects, Hmax and Hmax/Mmax ratios were significantly decreased in the standing position compared to the prone position (Hmax: p = 0.000, Hmax/Mmax: p = 0.016). However, Hmax/Mmax ratios were increased in standing position on both sides in poststroke patients with spasticity (unaffected side: p = 0.006, affected side: p = 0.095). The Hmax and Hmax/Mmax ratios were significantly more increased on the affected side than unaffected side irrespective of the position.

Conclusions

The motor neuron excitability of both sides was not suppressed but instead upregulated in the standing position in subjects with spasticity, which may suggest that there was abnormal regulation of the Ia pathway on both sides.

Challenges to the Vestibular System in Space: How the Brain Responds and Adapts to Microgravity

In the next century, flying civilians to space or humans to Mars will no longer be a subject of science fiction. The altered gravitational environment experienced during space flight, as well as that experienced following landing, results in impaired perceptual and motor performance-particularly in the first days of the new environmental challenge. Notably, the absence of gravity unloads the vestibular otolith organs such that they are no longer stimulated as they would be on earth. Understanding how the brain responds initially and then adapts to altered sensory input has important implications for understanding the inherent abilities as well as limitations of human performance. Space-based experiments have shown that altered gravity causes structural and functional changes at multiple stages of vestibular processing, spanning from the hair cells of its sensory organs to the Purkinje cells of the vestibular cerebellum. Furthermore, ground-based experiments have established the adaptive capacity of vestibular pathways and neural mechanism that likely underlie this adaptation. We review these studies and suggest that the brain likely uses two key strategies to adapt to changes in gravity: (i) the updating of a cerebellum-based internal model of the sensory consequences of gravity; and (ii) the re-weighting of extra-vestibular information as the vestibular system becomes less (i.e., entering microgravity) and then again more reliable (i.e., return to earth).

Effect of Incorporating Short-Foot Exercises in the Balance Rehabilitation of Flat Foot: A Randomized Controlled Trial

Effective balance rehabilitation is essential to address flat foot (pes planus) which is closely associated with reduced postural stability. Although sensorimotor training (SMT) and short-foot exercise (SFE) have been effective for improving postural stability, the combined effects of SMT with SFE have not been evaluated in previous studies. The aim of this study was to compare the lone versus combined effects of SMT with SFE on postural stability among participants with flat foot. This was a single-blinded, randomized controlled trial. A total of 32 flat-footed participants were included in the study (14 males and 18 females) and assigned to the SMT combined with SFE group and SMT alone group. All participants underwent 18 sessions of the SMT program three times a week for six weeks. Static balance, dynamic balance, and the H_max/M_max ratio were compared before and after the interventions. Static and dynamic balance significantly increased in the SMT combined with SFE group compared with the SMT alone group. However, the H_max/M_max ratio was not significantly different between the two groups. Therefore, this study confirms that the combination of SMT and SFE is superior to SMT alone to improve postural balance control in flat-footed patients in clinical settings.

Effect of posture and body weight loading on spinal posterior root reflex responses

The posterior root muscle response (PRM) is a monosynaptic reflex that is evoked by single pulse transcutaneous spinal cord stimulation (tSCS). The main aim of this work was to analyse how body weight loading influences PRM reflex threshold measured from several lower limb muscles in healthy participants. PRM reflex responses were evoked with 1-ms rectangular monophasic pulses applied at an interval of 6 s via a self-adhesive electrode (9 × 5 cm) at the T11-T12 vertebral level. Surface electromyographic activity of lower limb muscles was recorded during four different conditions, one in decubitus supine (DS) and the other three involving standing at 100%, 50%, and 0% body weight loading (BW). PRM threshold intensity, peak-to-peak amplitude, and latency for each muscle were analysed in different conditions study. PRM reflex threshold increased with body weight unloading compared with DS, and the largest change was observed between DS and 0% BW for the proximal muscles and between DS and 50% BW for distal muscles. Peak-to-peak amplitude analysis showed only a significant mean decrease of 34.6% (SD 10.4, p = 0.028) in TA and 53.6% (SD 15.1, p = 0.019) in GM muscles between DS and 50% BW. No significant differences were observed for PRM latency. This study has shown that sensorimotor networks can be activated with tSCS in various conditions of body weight unloading. Higher stimulus intensities are necessary to evoke reflex response during standing at 50% body weight loading. These results have practical implications for gait rehabilitation training programmes that include body weight support.

Effect of inhibitory kinesiotaping on spasticity in patients with chronic stroke: a randomized controlled pilot trial

BACKGROUND

There is no consensus regarding the positive effect of kinesiotaping (KT) on spasticity. All previous studies have measured spasticity by Modified Ashworth Scale (MAS) scale which is a subjective clinical assessment.

OBJECTIVE

To investigate the effect of inhibitory KT on the spasticity of plantar flexor muscles using both Hoffmann-reflex (H-reflex) and MAS scale. H-reflex is a neurophysiological technique that objectively evaluates spasticity by reflecting the excitability of motor neurons.

METHODS

Thirty patients were randomly assigned into inhibitory KT (n = 15) and control (n = 15) groups. The inhibitory KT group received KT from insertion to the origin of gastrocsoleus muscle . Spasticity was assessed at baseline and 30 min and 48 h after taping by H-reflex and MAS scale. The control group received no taping and spasticity was assessed at baseline and 30 min and 48 h after the baseline.

RESULT

There was a significant time × group effect for the maximal peak-to-peak amplitude of the H_max/M_max ratio (p = .007), indicating that H_max/M_max ratio decreased significantly after 48 h in the inhibitory KT in comparison with the baseline (P = .001) and 30 min after-intervention (p = .002); meanwhile, it did not change significantly in the control group (P > .05). However, none of the groups showed a statistically significant change in MAS score (P > .05).

CONCLUSIONS

Application of inhibitory KT was found to be able to reduce the H_max/M_max ratio in patients with stroke. As a result, inhibitory KT could have beneficial effects on spasticity.

Acute Effects of Kinesiology Taping Stretch Tensions on Soleus and Gastrocnemius H-Reflex Modulations

This study examined the acute effects of stretch tensions of kinesiology taping (KT) on the soleus (SOL), medial (MG), and lateral (LG) gastrocnemius Hoffmann-reflex (H-reflex) modulation in physically active healthy adults. A cross-over within-subject design was used in this study. Twelve physically active collegiate students voluntarily participated in the study (age = 21.3 ± 1.2 years; height = 175.6 ± 7.1 cm; body weight = 69.9 ± 7.1 kg). A standard Y-shape of KT technique was applied to the calf muscles. The KT was controlled in three tension intensities in a randomised order: paper-off, 50%, and 100% of maximal stretch tension of the tape. The peak-to-peak amplitude of maximal M-wave (M_max) and H-reflex (H_max) responses in the SOL, MG, and LG muscles were assessed before taping (pre-taping), taping, and after taping (post-taping) phases in the lying prone position. The results demonstrated significantly larger LG H_max responses in the pre-taping condition than those in the post-taping condition during paper-off KT (p = 0.002). Moreover, the ΔH_max/M_max of pre- and post-taping in the SOL muscle was significantly larger during 50%KT tension than that of paper-off (p = 0.046). In conclusion, the stretch tension of KT contributes minor influence on the spinal motoneuron excitability in the triceps surae during rest.

Effect of Acute Heart Rate Variability Biofeedback on H-reflex Modulation: A Pilot Study

Heart rate variability biofeedback (HRV BFB) is paced breathing scheme that stimulates resonance in the cardiovascular system. This study aimed to investigate the effect of a single-session HRV BFB on Hoffman reflex (H-reflex) of the soleus muscle. Twelve healthy males (height: 173.7 ± 7.18 cm; weight: 72.7 ± 17.7 kg; age: 24.0 ± 5.02 yrs) completed a randomized-crossover intervention involving a 10-minute HRV BFB and normal breathing (CON) separated by 48 hours. Results revealed significantly lower 1a afferent activation after HRV BFB. Similarly, the HRV BFB also demonstrated lower proportion of activated motor neurons from 1a afferents. In conclusion, an acute HRV BFB influenced the reduction in motoneuron excitability at resting condition.

Wearing compression garments differently affects monopodal postural balance in high-level athletes

This study investigated the acute effects of compression garments (CG) on balance control in elite athletes. 15 male professional handball players were recruited. They had to stand as motionless as possible in a monopedal stance on a force plate with the eyes closed and on a wobble board with the eyes open, while wearing CG or not. Centre of foot pressure mean velocity and surface area were calculated. Statistics were first calculated with the data from the whole sample. A hierarchical cluster analysis was also performed in order to categorize the participants’ behaviours into subgroups with similar characteristics. The whole group analysis showed that there were no significant effects attributed to CG. The clustering analysis identified two distinct and homogeneous subgroups of participants. Only athletes with the best balance abilities at baseline could benefit from CG wearing to improve their balance control. These athletes, who swayed less and were more sensitive to somatosensory manipulation due to CG wearing, seem to control balance by adopting a support-dependent preferred sensorimotor tactic. Our findings suggest that amongst high-level athletes, the ability to benefit from CG wearing to improve balance control seems to depend on participants’ intrinsic balance skills and/or preferred sensorimotor tactics.

Acute effects of kinesiology tape tension on soleus muscle h-reflex modulations during lying and standing postures

Kinesiology tape (KT) has been widely used in the areas of sports and rehabilitation. However, there is no gold standard for the tape tension used during a KT application. The purpose of this study was to examine the effects of KT application with different tension intensities on soleus muscle Hoffmann-reflex (H-reflex) modulation during lying and standing postures. Fifteen healthy university students were tested with 3 tape tension intensities during separate visits with a randomized sequence: tape-on no tension (0KT), moderate (about 50% of the maximal tape tension: (ModKT), and maximal tape tension (MaxKT). During each experimental visit, the H-reflex measurements on the soleus muscle were taken before, during, and after the KT application for both lying and standing postures. The H-wave and M-wave recruitment curves were generated using surface electromyography (EMG). There was a main effect for posture (p = 0.001) for the maximal peak-to-peak amplitude of the H-wave and M-wave (H_max/M_max) ratio, showing the depressed H_max/M_max ratio during standing, when compared to the lying posture. Even though the tension factor had a large effect (η_p² = 0.165), different tape tensions showed no significant differential effects for the H_max/M_max ratio. The spinal motoneuron excitability was not altered, even during the maximal tension KT application on the soleus muscle. Thus, the tension used during a KT application should not be a concern in terms of modulating the sensorimotor activity ascribed to elastic taping during lying and standing postures.

Sensory Sub- and Suprathreshold TENS Exhibit No Immediate Effect on Postural Steadiness in Older Adults with No Balance Impairments

Transcutaneous electrical nerve stimulation (TENS) has been reported to attenuate postural sway; however, the results are inconclusive, with some indicating the effect and others not. The study aimed to evaluate the effect of sensory sub- and suprathreshold low-frequency TENS applied through the plantar surface and posterior aspect of shanks on postural sway. In a group of healthy community-dwelling older adults, TENS was delivered with two different current intensities: (1) subsensory which is below conscious perception and (2) suprasensory threshold which is within the range of conscious perception. Frequencies of the TENS stimulation were sweeping from 5 to 180 Hz and were delivered through the plantar surface and posterior shanks of both legs. Postural sway was measured with a force platform in eyes-open and eyes-closed conditions. To evaluate potential fast adaptability to TENS stimuli, the results were evaluated in two time intervals: 30 seconds and 60 seconds. The results indicated that TENS with the chosen frequencies and electrode placement did not affect postural sway in both the sub- and suprathreshold intensities of TENS, in eyes-open and eyes-closed conditions, and in 30-second and 60-second time intervals. In conclusion, given that in this study sub- and suprathreshold TENS applied via the plantar surface of the feet did not attenuate postural sway, it would be easy to conclude that this type of electrical stimuli is ineffective and no further research is required. We must caution against this, given the specificity of the electrode placements. We recommend that future research be performed consisting of individuals with balance impairments and with different positions of electrodes.

Modulation of the Hoffmann reflex in the tibialis anterior with a change in posture

Hoffmann (H-) reflex amplitudes in plantar flexor soleus muscle are modulated by posture, yet dorsiflexor tibialis anterior (TA) H-reflex parameters have sparingly been studied. The purpose was to investigate modulation of the TA H-reflex when postural demands are increased from sitting to standing. In this study, data from 18 participants (Age: 25 ± 4 years, Height: 170.9 ± 9.5 cm, Weight: 75.9 ± 17.2 kg) allowed comparison of two experimental conditions involving different postures (i.e. sitting and standing). Maximal amplitude of the TA H-reflex (Hmax ) as a percent of the maximal M-wave amplitude (Mmax ) (Hmax (% Mmax )) during sitting and standing was compared using ANOVA. Modulation of TA H-reflex amplitude was found: Eleven participants showed facilitation and seven showed no change of reflex amplitudes. Only participants in the facilitation group showed modulation related to changes in posture (sitting: 8.7 ± 2.9%; standing: 14.8 ± 6.7%, P = 0.005). These data provide evidence of the sensitivity to posture of TA H-reflexes. As with task-dependent changes in soleus H-reflexes, presynaptic regulation of Ia afferent transmission is a possible mechanism. Further investigations into causes of modulation are warranted.

Examining Neural Plasticity for Slip-Perturbation Training: An fMRI Study

Perturbation-based balance training has shown to induce adaptation of reactive balance responses that can significantly reduce longer-term fall risk in older adults. While specific cortical and subcortical areas in control of posture and locomotion have been identified, little is known about the training-induced plasticity occurring in neural substrates for challenging tasks involving reactive balance control. The purpose of this study was to use functional neuroimaging to examine and determine the neural substrates, if any, involved in inducing adaptation to slip-like perturbations experienced during walking over 3 consecutive training days. We used a mental imagery task to examine the neural changes accompanied by treadmill-slip perturbation training. Ten healthy young adults were exposed to increasing magnitude of displacements during slip-like perturbations while walking, with an acceleration of 6 m/s² on a motorized treadmill for 3 consecutive days. Brain activity was recorded through MRI while performing imagined slipping and imagined walking tasks before and after the perturbation training. The number of compensatory steps and center of mass state stability at compensatory step touchdown were recorded. As compared with day 1 (first trial), on day 3 (last trial) there was a significant reduction in number of compensatory steps and increase in stability at compensatory step touchdown on the mid and highest perturbation intensities. Before perturbation training, imagined slipping showed increased activity in the SMA, parietal regions, parahippocampal gyrus, and cingulate gyrus compared with rest. After perturbation training, imagined slipping showed increased activation in DLPFC, superior parietal lobule, inferior occipital gyrus, and lingual gyrus. Perturbation training was not associated with decline in activity in any of the brain regions. This study provides evidence for learning-related changes in cortical structures while adapting to slip-like perturbations while walking. The findings reflect that higher-level processing is required for timing and sequencing of movements to execute an effective balance response to perturbations. Specifically, the CNS relies on DLPFC along with motor, parietal, and occipital cortices for adapting to postural tasks posing a significant threat to balance.

Anticipatory and compensatory postural adjustments in people with low back pain: a systematic review and meta-analysis

BACKGROUND CONTEXT

Despite altered anticipatory (APAs) and compensatory postural adjustments (CPAs) being hypothesized to contribute to the onset and persistence of low back pain (LBP), results from studies comparing people with and without LBP are conflicting.

PURPOSE

This systematic review aimed to determine whether APAs or CPAs are altered in the presence of acute and chronic LBP.

STUDY DESIGN

A systematic review of studies was carried out.

PATIENT SAMPLE

No patient sample was required.

OUTCOME MEASURES

Between group standardized mean differences and 95% confidence intervals for APAs ad CPAs METHODS: A comprehensive search was conducted for articles comparing people with LBP (acute or chronic) to healthy controls for the onset or amplitude of muscle activity, center of pressure (COP), or kinematic responses to expected or unexpected perturbations. Two independent reviewers extracted data and assessed the methodological quality of relevant studies. Differences between people with and without LBP were calculated as standardized mean differences, and included in a meta-analysis if outcomes were homogeneous. Otherwise, a narrative synthesis was conducted.

RESULTS

Twenty-seven studies were included, of which the majority examined muscle onsets in response to expected and unexpected perturbations. Only two studies compared people with and without acute LBP, and results for these studies were conflicting. The results show delayed muscle onsets in response to expected and unexpected perturbations for people with chronic LBP when compared with healthy controls. No conclusive evidence for differences between people with and without chronic LBP for COP or kinematic responses.

CONCLUSIONS

There is currently no convincing evidence of differences between people with and without acute LBP for APAs or CPAs. Conversely, delayed muscle onsets in people with chronic LBP suggest APAs and CPAs are altered in this population. However, the functional relevance of these delayed muscle onsets (eg, COP and kinematics) is unknown.

The effect of augmented somatosensory feedback on standing postural sway

Impaired balance resulting from reduced postural control occurs with aging and various medical conditions. Sensory input for balance control is provided by the visual, vestibular and somatosensory systems. Previous research suggests that increased proprioceptive feedback from various lower extremity devices improves balance. Mixed results have been reported with the use of orthoses such as ankle foot orthoses (AFOs). In this study, 20 healthy subjects wore footplates in their shoes or straps around their lower legs in order to imitate the somatosensory feedback produced by wearing AFOs, but without providing ankle restriction. Subjects' standing balance was assessed using force plates and computerized dynamic posturography (the sensory organization test-SOT) to determine if either the footplates or the lower-leg straps would affect standing balance. The results revealed no significant difference with the use of the footplates, however, wearing the straps resulted in reduced postural sway for conditions when visual cue deprivation was combined with manipulation of somatosensory or vestibular feedback. This effect was more pronounced in participants with the poorest baseline measures of balance. These findings suggest that lower extremity devices, such as AFOs, may augment somatosensory feedback that could improve balance during challenging sensory deprivation conditions, independent of orthotic support at the ankle.

Cortical Contribution to Linear, Non-linear and Frequency Components of Motor Variability Control during Standing

Motor variability is an inherent feature of all human movements and reflects the quality of functional task performance. Depending on the requirements of the motor task, the human sensory-motor system is thought to be able to flexibly govern the appropriate level of variability. However, it remains unclear which neurophysiological structures are responsible for the control of motor variability. In this study, we tested the contribution of cortical cognitive resources on the control of motor variability (in this case postural sway) using a dual-task paradigm and furthermore observed potential changes in control strategy by evaluating Ia-afferent integration (H-reflex). Twenty healthy subjects were instructed to stand relaxed on a force plate with eyes open and closed, as well as while trying to minimize sway magnitude and performing a "subtracting-sevens" cognitive task. In total 25 linear and non-linear parameters were used to evaluate postural sway, which were combined using a Principal Components procedure. Neurophysiological response of Ia-afferent reflex loop was quantified using the Hoffman reflex. In order to assess the contribution of the H-reflex on the sway outcome in the different standing conditions multiple mixed-model ANCOVAs were performed. The results suggest that subjects were unable to further minimize their sway, despite actively focusing to do so. The dual-task had a destabilizing effect on PS, which could partly (by 4%) be counter-balanced by increasing reliance on Ia-afferent information. The effect of the dual-task was larger than the protective mechanism of increasing Ia-afferent information. We, therefore, conclude that cortical structures, as compared to peripheral reflex loops, play a dominant role in the control of motor variability.

The effect of a single massage based on the tensegrity principle on postural stability in young women

OBJECTIVE

The aim of this study was to investigate the effects of normalized muscle tension via tensegrity-based massage on postural stability in a sample of female young adults.

METHODS

Nineteen females aged 21.8 ± 1.9 years were recruited presenting abnormal tension at muscles adhering to any of the following structural sites: superior iliac spine, lateral sacropelvic surface, linea aspera at 1/2 of femur length, and superior nuchal line of the occiput. Balance and postural control were assessed during bipedal stance using a force platform in multiple conditions: hard surface or soft foam surface with the head in either a neutral posture or tilted backward. Baseline and 3-min and 15-min post-treatment measures were collected while barefoot and eyes closed. Main outcomes measures included center of pressure variability, range, radius, and velocity in the anteroposterior (AP) mediolateral (ML) dimensions.

RESULTS

In the solid surface with neutral head posture condition only AP COP measures decreased significantly (p< 0.05). In the soft surface condition, significant differences were observed in the AP and ML dimensions among most measures (p< 0.05).

CONCLUSIONS

A single application of tensegrity-based massage positively influenced postural control in young adult females, particularly in the AP direction.

Alleviation of Motor Impairments in Patients with Cerebral Palsy: Acute Effects of Whole-body Vibration on Stretch Reflex Response, Voluntary Muscle Activation and Mobility

INTRODUCTION

Individuals suffering from cerebral palsy (CP) often have involuntary, reflex-evoked muscle activity resulting in spastic hyperreflexia. Whole-body vibration (WBV) has been demonstrated to reduce reflex activity in healthy subjects, but evidence in CP patients is still limited. Therefore, this study aimed to establish the acute neuromuscular and kinematic effects of WBV in subjects with spastic CP.

METHODS

44 children with spastic CP were tested on neuromuscular activation and kinematics before and immediately after a 1-min bout of WBV (16-25 Hz, 1.5-3 mm). Assessment included (1) recordings of stretch reflex (SR) activity of the triceps surae, (2) electromyography (EMG) measurements of maximal voluntary muscle activation of lower limb muscles, and (3) neuromuscular activation during active range of motion (aROM). We recorded EMG of m. soleus (SOL), m. gastrocnemius medialis (GM), m. tibialis anterior, m. vastus medialis, m. rectus femoris, and m. biceps femoris. Angular excursion was recorded by goniometry of the ankle and knee joint.

RESULTS

After WBV, (1) SOL SRs were decreased (p < 0.01) while (2) maximal voluntary activation (p < 0.05) and (3) angular excursion in the knee joint (p < 0.01) were significantly increased. No changes could be observed for GM SR amplitudes or ankle joint excursion. Neuromuscular coordination expressed by greater agonist-antagonist ratios during aROM was significantly enhanced (p < 0.05).

DISCUSSION

The findings point toward acute neuromuscular and kinematic effects following one bout of WBV. Protocols demonstrate that pathological reflex responses are reduced (spinal level), while the execution of voluntary movement (supraspinal level) is improved in regards to kinematic and neuromuscular control. This facilitation of muscle and joint control is probably due to a reduction of spasticity-associated spinal excitability in favor of giving access for greater supraspinal input during voluntary motor control.

What Is the Contribution of Ia-Afference for Regulating Motor Output Variability during Standing?

Motor variability is an inherent feature of all human movements, and describes the system's stability and rigidity during the performance of functional motor tasks such as balancing. In order to ensure successful task execution, the nervous system is thought to be able to flexibly select the appropriate level of variability. However, it remains unknown which neurophysiological pathways are utilized for the control of motor output variability. In responding to natural variability (in this example sway), it is plausible that the neuro-physiological response to muscular elongation contributes to restoring a balanced upright posture. In this study, the postural sway of 18 healthy subjects was observed while their visual and mechano-sensory system was perturbed. Simultaneously, the contribution of Ia-afferent information for controlling the motor task was assessed by means of H-reflex. There was no association between postural sway and Ia-afference in the eyes open condition, however up to 4% of the effects of eye closure on the magnitude of sway can be compensated by increased reliance on Ia-afference. Increasing the biomechanical demands by adding up to 40% bodyweight around the trunk induced a specific sway response, such that the magnitude of sway remained unchanged but its dynamic structure became more regular and stable (by up to 18%). Such regular sway patterns have been associated with enhanced cognitive involvement in controlling motor tasks. It therefore appears that the nervous system applies different control strategies in response to the perturbations: The loss of visual information is compensated by increased reliance on other receptors; while the specific regular sway pattern associated with additional weight-bearing was independent of Ia-afferent information, suggesting the fundamental involvement of supraspinal centers for the control of motor output variability.

Measurement of Dynamic Joint Stiffness from Multiple Short Data Segments

This paper presents our new method, Short Segment-Structural Decomposition SubSpace (SS-SDSS), for the estimation of dynamic joint stiffness from short data segments. The main application is for data sets that are only piecewise stationary. Our approach is to: 1) derive a data-driven, mathematical model for dynamic stiffness for short data segments; 2) bin the non-stationary data into a number of short, stationary data segments; and 3) estimate the model parameters from subsets of segments with the same properties. This method extends our previous state-spacework by recognizing that initial conditions have important effects for short data segments; consequently, initial conditions are incorporated into the stiffness model and estimated for each segment. A simulation study that faithfully replicated experimental conditions delineated the range of experimental conditions for which the method can successfully identify stiffness. An experimental study on the ankle of a healthy subject during a torque matching tasks demonstrated the successful estimation of dynamic stiffness in a slow, time-varying experiment. Together, the simulation and experimental studies demonstrate that the SS-SDSS method is a valuable tool to measure stiffness in functionally important tasks.

A soft ankle brace increases soleus Hoffman reflex amplitude but does not modify presynaptic inhibition during upright standing

External ankle supports, such as ankle braces, may improve postural stability by stimulating cutaneous receptors. It remains unknown whether these supports have an effect on the posture central regulation. The aim of this study was to determine the effect of wearing a soft ankle brace on soleus H-reflex amplitude and presynaptic inhibition during standing. Sixteen subjects stood on a rigid floor with their eyes opened, either barefoot or wearing a soft ankle brace. H-reflex amplitude was measured on the soleus muscle by stimulating the tibial nerve electrically. Modulation of presynaptic inhibition was assessed by conditioning the H-reflex with fibular nerve (D1 inhibition) and femoral nerve (heteronymous facilitation) electrical stimulations. The unconditioned H-reflex amplitude was significantly greater when wearing the ankle brace than barefoot, whereas D1 and HF conditioned soleus H-reflex did not differ significantly between bracing conditions. These results suggest that the ankle brace increased the soleus motoneuron excitability without altering presynaptic mechanisms, potentially because of increased cutaneous mechanoreceptors afferent signals provided by the soft ankle brace.

Effect of cooling foot sole skin receptors on achilles tendon reflex

INTRODUCTION

This study investigated whether a controlled reduction of foot sole temperature affects the Achilles tendon stretch reflex and plantar flexion. Methods Five stretch reflexes in 52 healthy subjects were evoked by Achilles tendon taps. Short latency responses of 3 muscles of the lower limb and maximal force of plantar flexion were analyzed. Foot sole hypothermia was induced by a thermal platform at various foot temperature conditions: Stage I (25°C), Stage II (12°C), Stage IIIa (0°C), and Stage IIIb (0°C). Results Reduction of plantar cutaneous inputs resulted in a decrease in amplitude of medial gastrocnemius and soleus as well as delays in time to maximal force of plantar flexion. Medial gastrocnemius, lateral gastrocnemius, and soleus were affected differently by induced cooling. No inhibition effects in reflexes were observed at 12°C. Conclusions The results suggest that input on the plantar foot sole participates complementarily in the Achilles stretch reflex Muscle Nerve, 2015. Muscle Nerve 53: 965-971, 2016.