Analysis of shared synaptic inputs to different motor unit subgroups in triceps surae during a postural standing task.

Previously, we have observed differential firing behaviours and recruitment locations of distinct motor unit (MU) subgroups within the same muscles. This study examined the amount of shared synaptic inputs to these MU subgroups. Twenty-four participants (10 healthy young adults: 5 females, 5 males; mean ± SD: age 27 ± 2.

The effects of medial gastrocnemius muscle fatigue on regional modulation of the ankle plantarflexors during standing external perturbations.

The ankle plantarflexor muscles [medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL)] were shown to exhibit direction-specific regional modulation of muscle activity during external perturbations. This study investigated the effect of MG muscle fatigue on plantarflexor muscle activation patterns. It was hypothesized that fatigue of MG would be compensated for by changing the activity of the SOL and LG to maintain balance.

The effect of slow breathing on cardiovascular and electromyographic responses during standing perturbations in older adults.

A bi-directional interaction between the cardiovascular and postural control systems has been previously reported in young adults; however, limited data exist in older populations where physiological alternations in these systems are well known. The purpose of this study was to determine: (1) the effect of slow breathing on heart rate (HR) and systolic blood pressure (SBP) responses following surface support postural perturbations in older adults and (2) the effect of slow breathing on lower limb muscle burst onset and burst amplitude during postural perturbations of the support surface in older adults. Twenty community-dwelling older adults experienced posteriorly directed accelerations of treadmill belts during quiet standing while breathing spontaneously (SPON) or breathing at 6 breaths per minute (SLOW).

Perturbed walking balance recovery between premenopausal and postmenopausal females.

Background: Early postmenopausal females are at increased risk for falls and fragility fractures, despite often not meeting the diagnostic criteria for osteoporosis or showing noticeable declines in gait and balance.

Methods: Fifteen premenopausal females (aged 35-53) and fifteen postmenopausal females (aged 50-66) participated in this study. The Gait Real-time Analysis Interactive Laboratory was utilized to simulate unexpected perturbations during walking.

Regional recruitment and differential behavior of motor units during postural control in older adults.

Aging is associated with neuromuscular system changes that may have implications for the recruitment and firing behaviors of motor units (MUs). In previous studies, we observed that young adults recruit subpopulations of triceps surae MUs during tasks that involved leaning in five directions: common units that were active during different leaning directions and unique units that were active in only one leaning direction. Furthermore, the MU subpopulation firing behaviors [average firing rate (AFR), coefficient of variation (CoV), and intermittent firing] modulated with leaning direction.

Cardiovascular response to anticipatory and reactionary postural perturbations in young adults.

New Findings: What is the central question of this study? It has been suggested that the cardiovascular responses to a postural perturbation are centrally mediated and reflex mediated. We wanted to know the extent to which the cardiovascular responses to external perturbations could be executed in a feedforward manner, in anticipation of the perturbation. What is the main finding and its importance? We found no anticipatory component driving heart rate and systolic blood pressure responses, suggesting that reflexive mechanisms dominate cardiovascular regulation after a postural perturbation in young adults.

Differential behavior of distinct motoneuron pools that innervate the triceps surae.

It has been shown that when humans lean in various directions, the central nervous system (CNS) recruits different motoneuron pools for task completion; common units that are active during different leaning directions, and unique units that are active in only one leaning direction. We used high-density surface electromyography (HD-sEMG) to examine if motor unit (MU) firing behavior was dependent on leaning direction, muscle (medial and lateral gastrocnemius; soleus), limits of stability, or whether a MU is considered common or unique. Fourteen healthy participants stood on a force platform and maintained their center of pressure in five different leaning directions.

Cardiovascular response to postural perturbations of different intensities in healthy young adults.

The ability to regain control of balance is vital in limiting falls and injuries. Little is known regarding how the autonomic nervous system responds during recovery from balance perturbations of different intensities. The purpose of this study was to examine the cardiovascular response following a standing balance perturbation of varying intensities, quantify cardiac baroreflex sensitivity (cBRS) during standing perturbations, and to establish the stability of the cardiac baroreflex during quiet standing before and after balance disturbances.

Does the stimulus provoking a stepping reaction correlate with step characteristics and clinical measures of balance and mobility post-stroke?

Background: Retraining stepping reactions in people post-stroke is vital. However, the relationship between the stimulus and resulting stepping performance in people post-stroke is unknown. We explored relationships between stepping stimulus and stepping reactions initiated by either paretic or non-paretic legs of people post-stroke and controls.

Maintenance of standing posture during multi-directional leaning demands the recruitment of task-specific motor units in the ankle plantarflexors.

The purpose of this study is to investigate whether regional modulation of the ankle plantarflexors during standing was related to the recruitment of motor units associated with force direction. Fourteen participants performed a multi-directional leaning task in standing. Participants stood on a force platform and maintained their center of pressure in five different target directions.

Relationships Between Stepping-Reaction Movement Patterns and Clinical Measures of Balance, Motor Impairment, and Step Characteristics After Stroke.

Objective: Successful stepping reactions, led by either the paretic or nonparetic leg, in response to a loss of balance are critical to safe mobility poststroke. The purpose of this study was to measure sagittal plane hip, knee, ankle, and trunk kinematics during 2-step stepping reactions initiated by paretic and nonparetic legs of people who had stroke and members of a control group.

Methods: Principal component analysis (PCA) was used to reduce the data into movement patterns explaining interlimb coordination of the stepping and stance legs.

Neuroplasticity of Cortical Planning for Initiating Stepping Poststroke: A Case Series.

Background And Purpose: Therapeutic exercise improves balance and walking ability in individuals after stroke. The extent to which motor planning improves with therapeutic exercise is unknown. This case series examined how outpatient physical therapy affects motor planning and motor performance for stepping.

Effect of repetitive transcranial magnetic stimulation combined with robot-assisted training on wrist muscle activation post-stroke.

Objective: To compare the effects of active assisted wrist extension training, using a robotic exoskeleton (RW), with simultaneous 5 Hz (rTMS + RW) or Sham rTMS (Sham rTMS + RW) over the ipsilesional extensor carpi radialis motor cortical representation, on voluntary wrist muscle activation following stroke.

Methods: The two training conditions were completed at least one week apart in 13 participants >1-year post-stroke. Voluntary wrist extensor muscle activation (motor unit (MU) recruitment thresholds and firing rate modulation in a ramp-hold handgrip task), ipsilesional corticospinal excitability (motor evoked potential [MEP] amplitude) and transcallosal inhibition were measured Pre- and Post-training.

Challenging Standing Balance Reduces the Asymmetry of Motor Control of Postural Sway Poststroke.

Ankle plantarflexor muscle impairment contributes to asymmetrical postural control poststroke. This study examines the relationship of plantarflexor electromyography (EMG) with anterior-posterior center of pressure (APCOP) in people poststroke during progressive challenges to standing balance. Ten people poststroke and 10 controls participated in this study.

Symmetry of cortical planning for initiating stepping in sub-acute stroke.

Objective: This study examined motor planning for stepping when the paretic leg was either stepping or standing (to step with the non-paretic leg), to understand whether difficulty with balance and walking post-stroke could be attributed to poor motor planning.

Methods: Individuals with stroke performed self-initiated stepping. Amplitude and duration of the movement-related cortical potential (MRCP) was measured from Cz.

Do Performance Measures of Strength, Balance, and Mobility Predict Quality of Life and Community Reintegration After Stroke?

Objective: To investigate the extent to which physical performance measures of strength, balance, and mobility taken at discharge from inpatient stroke rehabilitation can predict health-related quality of life (HRQoL) and community reintegration after 6 months.

Design: Longitudinal study.

Setting: University laboratory.

Regionalization of the stretch reflex in the human vastus medialis.

Key Points: Regionalization of the stretch reflex, i.e. the notion that the activation of 1a afferents from a muscle region influences only the activation of motor units in the same region, has been demonstrated previously in animals but not in humans.

Regional activation within the vastus medialis in stimulated and voluntary contractions.

This study examined the contribution of muscle fiber orientation at different knee angles to regional activation identified with high-density surface electromyography (HDsEMG). Monopolar HDsEMG signals were collected using a grid of 13 × 5 electrodes placed over the vastus medialis (VM). Intramuscular electrical stimulation was used to selectively activate two regions within VM.

A single session of open kinetic chain movements emphasizing speed improves speed of movement and modifies postural control in stroke.

Little attention has been given to training speed of movement, even though functional activities require quick submaximal contractions. Closed kinetic chain (CKC) exercises are considered more functional; however, the best method for training speed is not known. A single bout of open kinetic chain (OKC) exercises emphasizing speed was performed to determine whether movement velocity and muscle activation would improve in a single session and whether the improvements transfer to a physiological balance task.

Motor Planning for Loading During Gait in Subacute Stroke.

Objectives: To determine the characteristics of motor planning surrounding initial contact during gait through examination of thigh muscle timing, amplitude, and co-contraction of the paretic and nonparetic limbs in people poststroke, and to investigate whether muscle timing, amplitude, and clinical performance measures of balance and mobility differ based on the level of co-contraction.

Design: Observational study.

Setting: University-based research laboratory.

Reliability of center of pressure measures within and between sessions in individuals post-stroke and healthy controls.

Background: Knowing the reliability of the center of pressure (COP) is important for interpreting balance deficits post-stroke, especially when the balance deficits can necessitate the use of short duration trials. The novel aspect of this reliability study was to examine the center of pressure measures using two adjacent force platforms between and within sessions in stroke and controls. After stroke, it is important to understand the contribution of the paretic and non-paretic leg to the motor control of standing balance.

Is the recovery of functional balance and mobility accompanied by physiological recovery in people with severe impairments after stroke?

Background: Rehabilitation after severe stroke is often limited because of impairments in sensorimotor function. Functional and physiological recovery after severe stroke is poorly understood and has not been studied extensively.

Objective: This study's purpose was to examine functional and physiological recovery of standing balance during inpatient rehabilitation in people with severe impairments after stroke.

Motoneurone afterhyperpolarisation time-course following stroke.

Objective: Our aim was to investigate any changes in the estimated time-course of the afterhyperpolarisation (AHP) in motoneurones innervating the tibialis anterior following stroke, with a secondary objective to compare the results from two different AHP estimation techniques.

Methods: Motor units from tibialis anterior on the paretic and non-paretic sides of 15 subjects with chronic stroke were recorded using intramuscular electrodes during voluntary isometric contraction. Participants varied the motor unit firing rate from its lowest rate to approximately 10 Hz.

Influence of vestibular afferent input on common modulation of human soleus motor units during standing.

The purpose of this study was to investigate whether application of bipolar galvanic vestibular stimulation (GVS) would influence the common modulation of motor unit discharge rate in bilateral soleus muscles during quiet standing. Soleus motor unit activity was recorded with fine wire electrodes in each leg. Subjects stood, with eyes closed, on two adjacent force platforms to record postural sway with the head facing straight ahead, turned to right, or turned left.