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1.  Muscle Strength and Weight-Bearing Symmetry Relate to Sit-to-Stand Performance in Individuals with Stroke 
Gait & posture  2005;22(2):126-131.
This study investigated the relationship of lower extremity joint torques and weight-bearing symmetry to sit-to-stand (STS) performance in individuals with chronic stroke. A motion analysis system and two force plates measured STS duration and weight-bearing symmetry (determined by ground reaction forces) during three self-paced and three fast-paced conditions. An isokinetic dynamometer measured maximum concentric joint torques of the paretic and nonparetic ankle, knee, and hip, which were normalized by body mass. Pearson correlations indicated that (a) paretic ankle dorsiflexion and knee extension torques related to the duration of the self-paced STS condition (r = −0.450, −0.716, respectively), (b) paretic ankle dorsiflexion, plantar flexion, and knee extension torques related to the duration of the fast-paced STS condition (r = −0.466, −0.616, −0.736, respectively), and (c) greater weight-bearing symmetry related to faster STS performance for both self-paced and fast-paced STS conditions (r = −0.565, −0.564, respectively) (p < 0.05). This evidence suggests that paretic muscle strength and the ability to load the paretic limb are important factors underlying the ability to rise from a chair in individuals with chronic stroke.
PMCID: PMC3167866  PMID: 16139747 CAMSID: cams1870
Stroke; Sit-to-stand; Torque; Weight-bearing
2.  Modulation of Ankle Muscle Postural Reflexes in Stroke: Influence of Weight-bearing Load 
Given the known sensorimotor deficits and asymmetric weight-bearing posture in stroke, the aim of this study was to determine whether stroke affects the modulation of standing postural reflexes with varying weight-bearing load.
Ten individuals with chronic stroke and 10 healthy older adult controls were exposed to unexpected forward and backward platform translations while standing. Three different stance conditions were imposed: increased weight-bearing load, decreased weight-bearing load, and self-selected stance. Surface EMG from bilateral ankle dorsiflexors (tibialis anterior) and extensors (gastrocnemius) were recorded and the magnitude of background muscle activity (prior to the platform translation) and postural reflex onset latency and magnitude (75 ms following reflex onset) were determined.
Load modulation of ankle extensors was found in controls and individuals with stroke. Although controls demonstrated modulation of ankle dorsiflexors to different loads, individuals with stroke did not show this modulation. Further, load did not change the onset latency of postural reflexes of the individuals with stroke.
The delayed paretic muscle onset latencies in conjunction with impaired modulation of ankle dorsiflexor postural reflexes may contribute to the instability and frequent falls observed among individuals with stroke.
The results provide some insight into standing postural reflexes following stroke.
PMCID: PMC3226800  PMID: 15546787 CAMSID: cams2000
postural control; reflex; weight-bearing; cerebrovascular accident
3.  Direction-Dependent Phasing of Locomotor Muscle Activity Is Altered Post-Stroke 
Journal of neurophysiology  2004;92(4):2207-2216.
A major contributor to impaired locomotion post-stroke is abnormal phasing of muscle activity. While inappropriate paretic muscle phasing adapts to changing body orientation, load, and speed, it remains unclear whether paretic muscle phasing adapts to reversal of locomotor direction. We examined muscle phasing in backward pedaling, a task that requires shifts in biarticular but not uniarticular muscle phasing relative to forward pedaling. We hypothesized that if paretic and neurologically intact muscle phasing adapt similarly, then paretic biarticular but not paretic uniarticular muscles would shift phasing in backward pedaling. Paretic and neurologically intact individuals pedaled forward and backward while recording electromyograms (EMGs) from vastus medialis (VM), soleus (SOL), rectus femoris (RF), semimembranosus (SM), and biceps femoris (BF). Changes in muscle phasing were assessed by comparing the probability of muscle activity in forward and backward pedaling throughout 18 pedaling cycles. Paretic uniarticular muscles (VM and SOL) showed phase-advanced activity in backward versus forward pedaling, whereas the corresponding neurologically intact muscles showed little to no phasing change. Paretic biarticular muscles were less likely than neurologically intact biarticular muscles to display phasing changes in backward pedaling. Paretic RF displayed no phase change during backward pedaling, and paretic BF displayed no consistent adaptation to backward pedaling. Paretic SM was the only muscle to display backward/forward phase changes that were similar to the neurologically intact group. We conclude that paretic uniarticular muscles are more susceptible and paretic biarticular muscles are less susceptible to direction-dependent phase shifts, consistent with altered sensory integration and impaired cortical control of locomotion.
PMCID: PMC3912995  PMID: 15175363
4.  Reliability of TMS Motor Evoked Potentials in Quadriceps of Subjects with Chronic Hemiparesis after Stroke 
Journal of the neurological sciences  2008;276(1-2):115-117.
Transcranial magnetic stimulation (TMS) non-invasively measures excitability of central motor pathways in humans and is used to characterize neuroplasticity after stroke. Using TMS to index lower extremity neuroplasticity after gait rehabilitation requires test-retest reliability. This study assesses the reliability of TMS-derived variables measured at bilateral quadriceps of chronic hemiparetic stroke survivors. Results support using measures of both paretic and nonparetic motor threshold, MEP latencies; and nonparetic MEP amplitudes. Implications for longitudinal research are discussed.
PMCID: PMC2662509  PMID: 18945450
TMS; Lower extremity; stroke; reliability; quadriceps; paretic
5.  Human genome comparison of paretic and nonparetic vastus lateralis muscle in patients with hemiparetic stroke 
Hemiparetic stroke leads to major skeletal muscle abnormalities, as illustrated by paretic leg atrophy, weakness, and spasticity. Furthermore, the hemiparetic limb muscle shifts to a fast-twitch muscle fiber phenotype with anaerobic metabolism. This study investigated whether skeletal muscle genes were altered in chronic hemiparetic stroke. The nonparetic leg muscle served as an internal control. We used Affymetrix microarray analysis to survey gene expression differences between paretic and nonparetic vastus lateralis muscle punch biopsies from 10 subjects with chronic hemiparetic stroke. Stroke latency was greater than 6 months. We found that 116 genes were significantly altered between the paretic and nonparetic vastus lateralis muscles. These gene differences were consistent with reported differences after stroke in areas such as injury and inflammation markers, the myosin heavy chain profile, and high prevalence of impaired glucose tolerance and type 2 diabetes. Furthermore, while many other families of genes were altered, the gene families with the most genes altered included inflammation, cell cycle regulation, signal transduction, metabolism, and muscle contractile protein genes. This study is an early step toward identification of specific gene regulatory pathways that might lead to these differences, propagate disability, and increase vascular disease risk.
PMCID: PMC3024241  PMID: 18566945
cell cycle; gene expression; hemiparetic stroke; inflammation; metabolism; microarray; muscle contraction; rehabilitation; skeletal muscle; transcription factors; vastus lateralis
6.  Ankle Training With a Robotic Device Improves Hemiparetic Gait After a Stroke 
Task-oriented therapies such as treadmill exercise can improve gait velocity after stroke, but slow velocities and abnormal gait patterns often persist, suggesting a need for additional strategies to improve walking.
To determine the effects of a 6-week visually guided, impedance controlled, ankle robotics intervention on paretic ankle motor control and gait function in chronic stroke.
This was a single-arm pilot study with a convenience sample of 8 stroke survivors with chronic hemiparetic gait, trained and tested in a laboratory. Subjects trained in dorsiflexion–plantarflexion by playing video games with the robot during three 1-hour training sessions weekly, totaling 560 repetitions per session. Assessments included paretic ankle ranges of motion, strength, motor control, and overground gait function.
Improved paretic ankle motor control was seen as increased target success, along with faster and smoother movements. Walking velocity also increased significantly, whereas durations of paretic single support increased and double support decreased.
Robotic feedback training improved paretic ankle motor control with improvements in floor walking. Increased walking speeds were comparable with reports from other task-oriented, locomotor training approaches used in stroke, suggesting that a focus on ankle motor control may provide a valuable adjunct to locomotor therapies.
PMCID: PMC3565577  PMID: 21115945
stroke; rehabilitation; anklebot; ankle robot; hemiparetic gait
7.  Stroke-Related Changes in Neuromuscular Fatigue of the Hip Flexors and Functional Implications 
To compare stroke-related changes in hip-flexor neuromuscular fatigue of the paretic leg during a sustained, isometric sub-maximal contraction with the non-paretic leg and controls, and correlate fatigue with clinical measures of function.
Hip torques were measured during a fatiguing hip-flexion contraction at 20% of the hip flexion maximal voluntary contraction (MVC) in the paretic and non-paretic legs of 13 people with chronic stroke and 10 age-matched controls. In addition, participants with stroke performed a fatiguing contraction of the paretic leg at the absolute torque equivalent to 20% MVC of the non-paretic leg and were tested for self-selected walking speed (Ten-Meter Walk Test) and balance (Berg).
When matching the non-paretic target torque, the paretic hip flexors had a shorter time to task failure compared with the non-paretic leg and controls (p<0.05). Time to failure of the paretic leg was inversely correlated with the reduction of hip flexion MVC torque. Self-selected walking speed was correlated with declines in torque and steadiness. Berg-Balance scores were inversely correlated with the force fluctuation amplitude.
Fatigue and precision of contraction are correlated with walking function and balance post stroke.
PMCID: PMC3940208  PMID: 22157434
Neuromuscular Fatigue; Hip Flexors; Stroke
8.  Sit-to-Stand 3 months after Unilateral Total Knee Arthroplasty: Comparison of Self-Selected and Constrained Conditions 
Gait & posture  2009;30(2):187-191.
After unilateral total knee arthroplasty (TKA), rehabilitation specialists often constrain knee angles or foot positions during sit-to-stand, to encourage increased weight bearing through the operated limb. Biomechanical studies often constrain limb position during sit-to-stand in an effort to reduce variability. Differences between self-selecting or constraining position are unknown in persons after TKA. Twenty-six subjects with unilateral TKA participated in motion analysis. Subjects performed the sit-to-stand using a self-selected position (ssSTS); next, trials were collected in a constrained condition (ccSTS), where both knees were positioned with the tibia vertical, perpendicular to the floor. Repeated measures ANOVA (limb × condition) assessed differences between limbs and between conditions. Subjects used greater hip flexion bilaterally during ccSTS (91°) compared to ssSTS (87°; p=0.001) and knee flexion on the non-operated limb was greater during ssSTS (84°) compared to ccSTS (82°; p=0.018). The ccSTS resulted in larger extensor moments on the non-operated limb at the hip (ssSTS -0.473, ccSTS -0.521; p=0.021) and knee (ssSTS -0.431, ccSTS -0.457; p=0.001) compared to the operated limb. The ccSTS exacerbated the asymmetries at the hip and knee compared to ssSTS, and did not improve use of the operated limb. Reliance on the non-operated limb may put them at risk for progression of osteoarthritis in other joints of the lower extremities.
PMCID: PMC2729397  PMID: 19473843
sit-to-stand; total knee arthroplasty; altered movement pattern
9.  A paradox: after stroke the non-lesioned lower limb motor cortex may be maladaptive 
The European journal of neuroscience  2010;32(6):1032-1039.
What are the neuroplastic mechanisms that allow some stroke patients to regain high quality control of their paretic leg, while others do not? One theory implicates ipsilateral corticospinal pathways projecting from the non-lesioned hemisphere. We devised a new transcranial magnetic stimulation protocol to identify ipsilateral corticospinal tract conductivity from the non-lesioned hemisphere to the paretic limb in chronic stroke patients. We also assessed corticospinal tract degeneration using diffusion tensor imaging and used an ankle tracking task to assess lower limb motor control. We found greater tracking error during antiphase bilateral ankle movement for patients with strong conductivity from the non-lesioned hemisphere to paretic ankle than those with weak or no conductivity. These findings suggest that, instead of assisting motor control, contributions to lower limb motor control from the non-lesioned hemisphere of some stroke survivors may be maladaptive.
PMCID: PMC2943014  PMID: 20722719
lower extremity; neuroplasticity; TMS; DTI; stroke
10.  Progressive Shoulder Abduction Loading is a Crucial Element of Arm Rehabilitation in Chronic Stroke 
Total reaching range of motion (work area) diminishes as a function of shoulder abduction loading in the paretic arm in individuals with chronic hemiparetic stroke. This occurs when reaching outward against gravity or during transport of an object.
This study implements 2 closely related impairment-based interventions to identify the effect of a subcomponent of reaching exercise thought to be a crucial element in arm rehabilitation.
A total of 14 individuals with chronic moderate to severe hemiparesis participated in the participant-blinded, randomized controlled study. The experimental group progressively trained for 8 weeks to actively support the weight of the arm, up to and beyond, while reaching to various outward targets. The control group practiced the same reaching tasks with matched frequency and duration with the weight of the arm supported. Work area and isometric strength were measured before and after the intervention.
Change scores for work area at 9 loads were calculated for each group. Change scores were significantly larger for the experimental group indicating a larger increase in work area, especially shoulder abduction loads equivalent to those experienced during object transport. Changes in strength were not found within or between groups.
Progressive shoulder abduction loading can be utilized to ameliorate reaching range of motion against gravity. Future work should investigate the dosage response of this intervention, as well as test whether shoulder abduction loading can augment other therapeutic techniques such as goal-directed functional task practice and behavioral shaping to enhance real-world arm function.
PMCID: PMC2833097  PMID: 19454622
Stroke; Upper extremity; Shoulder loading; Biomechanics; Rehabilitation; Muscle strength; Robotics
11.  Test-retest reliability of Motricity Index strength assessments for lower extremity in post stroke hemiparesis 
The Motricity Index was used to measure strength in upper and lower extremities after stroke. The weighted score based on the ordinal 6 point scale of Medical Research Council was used to measure maximal isometric muscle strength. There is dearth of articles dealing with the reliability of this method. Therefore, the aim of this study was to determine the test retest reliability of Motricity Index strength assessments for paretic lower limb in 20 chronic stroke patients with one week interval.
In a cross sectional study, intrarater reliability of lower extremity Motricity Index strength assessments with one week interval were measured.
The SPSS 18 was used for analysis of data. Two-way random-consistency model of ICC was used for assessment of test-retest reliability. The ICC values showed high reliability of strength measurement of Motricity Index (ICC=0.93).
The Motricity Index can be a reliable instrument for measuring the strength of involved lower extremity when assessment is done by one rater following chronic stroke.
PMCID: PMC3587895  PMID: 23483112
Reliability; Motricity Index; Hemiparesis; Chronic stroke
12.  Muscle torque preservation and physical activity in individuals with stroke 
A greater percent loss of concentric versus eccentric muscle torque (i.e., relative eccentric muscle torque preservation) has been reported in the paretic limb of individuals with stroke and has been attributed to hypertonia and/or co-contractions. Stroke provides a unique condition for examining mechanisms underlying eccentric muscle preservation because both limbs experience similar amounts of general physical activity, but the paretic side is impaired directly by the brain lesion.
The purpose of this study was to determine 1) whether eccentric preservation also exists in the nonparetic limb and 2) the relationship of eccentric or concentric torque preservation with physical activity in stroke. We hypothesized that the nonparetic muscles would demonstrate eccentric muscle preservation, which would suggest that non-neural mechanisms may also contribute to its relative preservation.
Eighteen stroke and 18 healthy control subjects (age and sex matched) completed a physical activity questionnaire. Maximum voluntary concentric and eccentric joint torques of the ankle, knee and hip flexors and extensors were measured using an isokinetic dynamometer at 30°/s for the paretic and nonparetic muscles. Relative concentric and eccentric peak torque preservation were expressed as a percentage of control subject torque.
Relative eccentric torque was higher (more preserved) than relative concentric torque for paretic, as well as nonparetic muscles. Physical activity correlated with paretic (r=0.640, p=0.001) and nonparetic concentric torque preservation (r=0.508, p=0.009), but not with eccentric torque preservation for either leg.
The relative preservation of eccentric torque in the nonparetic muscles suggest a role of non-neural mechanisms and could also explain the preservation observed in other chronic health conditions. Loss of concentric, but not eccentric muscle torque was related to physical inactivity in stroke.
PMCID: PMC3114014  PMID: 19516167 CAMSID: cams1776
strength; rehabilitation; force; CVA
13.  Involuntary paretic wrist/finger flexion forces and EMG increase with shoulder abduction load in individuals with chronic stroke 
Clinical observations of the flexion synergy in individuals with chronic hemiparetic stroke describe coupling of shoulder, elbow, wrist, and finger joints. Yet, experimental quantification of the synergy within a shoulder abduction (SABD) loading paradigm has focused only on shoulder and elbow joints. The paretic wrist and fingers have typically been studied in isolation. Therefore, this study quantified involuntary behavior of paretic wrist and fingers during concurrent activation of shoulder and elbow.
Eight individuals with chronic moderate-to-severe hemiparesis and four controls participated. Isometric wrist/finger and thumb flexion forces and wrist/finger flexor and extensor electromyograms (EMG) were measured at two positions when lifting the arm: in front of the torso and at maximal reaching distance. The task was completed in the ACT3D robotic device with six SABD loads by paretic, non-paretic, and control limbs.
Considerable forces and EMG were generated during lifting of the paretic arm only, and they progressively increased with SABD load. Additionally, the forces were greater at the maximal reach position than at the position front of the torso.
Flexion of paretic wrist and fingers is involuntarily coupled with certain shoulder and elbow movements.
Activation of the proximal upper limb must be considered when seeking to understand, rehabilitate, or develop devices to assist the paretic hand.
PMCID: PMC3729226  PMID: 22364723
14.  The bilateral movement condition facilitates maximal but not submaximal paretic-limb grip force in people with post-stroke hemiparesis 
Clinical Neurophysiology  2012;123(8):1616-1623.
Although healthy individuals have less force production capacity during bilateral muscle contractions compared to unilateral efforts, emerging evidence suggests that certain aspects of paretic upper limb task performance after stroke may be enhanced by moving bilaterally instead of unilaterally. We investigated whether the bilateral movement condition affects grip force differently on the paretic side of people with post-stroke hemiparesis, compared to their non-paretic side and both sides of healthy young adults.
Within a single session, we compared: 1) maximal grip force during unilateral vs. bilateral contractions on each side, and 2) force contributed by each side during a 30% submaximal bilateral contraction.
Healthy controls produced less grip force in the bilateral condition, regardless of side (- 2.4% difference), and similar findings were observed on the non-paretic side of people with hemiparesis (- 4.5% difference). On the paretic side, however, maximal grip force was increased by the bilateral condition in most participants (+11.3% difference, on average). During submaximal bilateral contractions in each group, the two sides each contributed the same percentage of unilateral maximal force.
The bilateral condition facilitates paretic limb grip force at maximal, but not submaximal levels.
In some people with post-stroke hemiparesis, the paretic limb may benefit from bilateral training with high force requirements.
PMCID: PMC3335924  PMID: 22248812
stroke; upper extremity; interhemispheric inhibition; bilateral deficit; strength; human
15.  Rating of Everyday Arm-Use in the Community and Home (REACH) Scale for Capturing Affected Arm-Use after Stroke: Development, Reliability, and Validity 
PLoS ONE  2013;8(12):e83405.
To develop a brief, valid and reliable tool [the Rating of Everyday Arm-use in the Community and Home (REACH) scale] to classify affected upper limb use after stroke outside the clinical setting.
Focus groups with clinicians, patients and caregivers (n = 33) and a literature review were employed to develop the REACH scale. A sample of community-dwelling individuals with stroke was used to assess the validity (n = 96) and inter-rater reliability (n = 73) of the new scale.
The REACH consists of separate scales for dominant and non-dominant affected upper limbs, and takes five minutes to administer. Each scale consists of six categories that capture ‘no use’ to ‘full use’. The intraclass correlation coefficient and weighted kappa for inter-rater reliability were 0.97 (95% confidence interval: 0.95–0.98) and 0.91 (0.89–0.93) respectively. REACH scores correlated with external measures of upper extremity use, function and impairment (rho = 0.64–0.94).
The REACH scale is a reliable, quick-to-administer tool that has strong relationships to other measures of upper limb use, function and impairment. By providing a rich description of how the affected upper limb is used outside of the clinical setting, the REACH scale fills an important gap among current measures of upper limb use and is useful for understanding the long term effects of stroke rehabilitation.
PMCID: PMC3865179  PMID: 24358282
16.  The need for speed: Better movement quality during faster task performance after stroke 
Although slow and insufficient muscle activation is a hallmark of hemiparesis post-stroke, movement speed is rarely emphasized during upper extremity rehabilitation. Moving faster may increase intensity of task-specific training, but positive and/or negative effects on paretic-limb movement quality are unknown.
To determine whether moving quickly instead of at a preferred speed either enhances or impairs paretic limb task performance after stroke.
Sixteen people with post-stroke hemiparesis and 11 healthy controls performed reach-grasp-lift movements at their preferred speed and as fast as possible, using palmar and 3-finger grip types. We measured durations of the reach and grasp phases, straightness of the reach path, thumb-index finger separation (aperture), efficiency of finger movement, and grip force.
As expected, reach and grasp phase durations decreased in the fast condition in both groups, showing that participants were able to move more quickly when asked. When moving fast, the hemiparetic group had reach durations equal to those of healthy controls moving at their preferred speed. Movement quality also improved. Reach paths were straighter and peak apertures were greater in both groups in the fast condition. The group with hemiparesis also showed improved efficiency of finger movement. Differences in peak grip force across speed conditions did not reach significance.
People with hemiparesis are able to move faster than they choose to, and when they do, movement quality is improved. Simple instructions to move faster could be a cost-free and effective means of increasing rehabilitation intensity after stroke.
PMCID: PMC3325333  PMID: 22140198
hemiparesis; speed; kinematics; upper extremity; motor control; reach-to-grasp
17.  Comparison of the Plantar Pressure Distributions at Different Degrees of Tilting: A Preliminary Report 
[Purpose] The purpose of this study was to investigate the amount of plantar pressures on the lower limb during tilt table standing and to indicate the ideal degree of tilting for partial weight bearing. [Subjects and Methods] Fifteen healthy subjects between the ages of 20 and 30 were recruited as volunteers for this study. All the measurements were taken while standing on a tilt table according to different inclination angles. [Results] The plantar pressures for 60° tilt table standing were lower by 7–9% of total body weight than the pressures during tilt table standing at 90°, and the pressures for 30° tilt table standing were lower by 18–20% of total body weight than the pressures for tilt table standing at 90°. [Conclusion] Standing training on a 60° tilt table might be equivalent to 80% of full weight bearing training, and tilt table standing training at 30° might be equivalent to 60% of full weight bearing training.
PMCID: PMC3976011
Tilt table standing; Partial weight bearing; Standing training
18.  The Relationship of Asymmetric Weight-bearing with Postural Sway and Visual Reliance in Stroke 
Gait & posture  2006;23(2):249-255.
Due to motor and sensory deficits in individuals with stroke, we proposed that they must compensate for these impairments during standing with greater dependence on vision. In addition, we hypothesized that asymmetric weight-bearing, which occurs following stroke, is related to increased postural sway and those with greater asymmetry will have greater reliance on vision. Twenty-eight individuals with stroke and 28 healthy older adult controls stood quietly with eyes open or closed on a force platform while postural sway was quantified by centre of pressure measures and weight-bearing asymmetry was calculated from vertical ground reaction forces. To determine the influence of vision on postural sway, a visual ratio (eyes open/eyes closed) was calculated for the sway measures. The results demonstrated that individuals with stroke had greater visual dependence for the control of postural sway velocity in the medial-lateral, but not anterior-posterior direction, compared to controls. Further, we found that greater asymmetry was moderately related to increased medial-lateral sway for the individuals with stroke. Contrary to predictions, those individuals with stroke with mild asymmetry had greater visual dependence than those with more severe asymmetry.
PMCID: PMC3167822  PMID: 16399522 CAMSID: cams1869
postural control; cerebrovascular accident; balance
19.  Lower Extremity Passive Range of Motion in Community-Ambulating Stroke Survivors 
Physical therapists may prescribe stretching exercises for individuals with stroke to improve joint integrity and to reduce the risk of secondary musculoskeletal impairment. While deficits in passive range of motion (PROM) exist in stroke survivors with severe hemiparesis and spasticity, the extent to which impaired lower extremity PROM occurs in community-ambulating stroke survivors remains unclear. This study compared lower extremity PROM in able-bodied individuals and independent community-ambulatory stroke survivors with residual stroke-related neuromuscular impairments. Our hypothesis was that the stroke group would show decreased lower extremity PROM in the paretic but not the nonparetic side and that decreased PROM would be associated with increased muscle stiffness and decreased muscle length.
Individuals with chronic poststroke hemiparesis who reported the ability to ambulate independently in the community (n = 17) and age-matched control subjects (n = 15) participated. PROM during slow (5 degrees/sec) hip extension, hip flexion, and ankle dorsiflexion was examined bilaterally using a dynamometer that measured joint position and torque. The maximum angular position of the joint (ANGmax), torque required to achieve ANGmax (Tmax), and mean joint stiffness (K) were measured. Comparisons were made between able-bodied and paretic and able-bodied and nonparetic limbs.
Contrary to our expectations, between-group differences in ANGmax were observed only during hip extension in which ANGmax was greater bilaterally in people post-stroke compared to control subjects (P ≤ 0.05; stroke = 13 degrees, able-bodied = −1 degree). Tmax, but not K, was also significantly higher during passive hip extension in paretic and nonparetic limbs compared to control limbs (P ≤ 0.05; stroke = 40 Nm, able-bodied = 29 Nm). Compared to the control group, Tmax was increased during hip flexion in the paretic and nonparetic limbs of post-stroke subjects (P ≤ 0.05, stroke = 25 Nm, able-bodied = 18 Nm). K in the nonparetic leg was also increased during hip flexion (P ≤ 0.05, nonparetic = 0.52 Nm/degree, able-bodied = 0.37 Nm/degree.)
This study demonstrates that community-ambulating stroke survivors with residual neuromuscular impairments do not have decreased lower extremity PROM caused by increased muscle stiffness or decreased muscle length. In fact, the population of stroke survivors examined here appears to have more hip extension PROM than age-matched able-bodied individuals. The clinical implications of these data are important and suggest that lower extremity PROM may not interfere with mobility in community-ambulating stroke survivors. Hence, physical therapists may choose to recommend activities other than stretching exercises for stroke survivors who are or will become independent community ambulators.
PMCID: PMC3963266  PMID: 18463552
cerebral vascular accident (CVA); hemiparesis; muscle; range of motion (ROM); spasticity
20.  Neuromuscular performance of paretic versus non-paretic plantar flexors after stroke 
European Journal of Applied Physiology  2011;111(12):3041-3049.
The objective of this study was to compare the neuromuscular function of the paretic and non-paretic plantar flexors (i.e. soleus, gastrocnemius medialis, lateralis) in chronic stroke patients. It was hypothesized that the contractile rate of force development (RFD) and neural activation, assessed by electromyogram (EMG) and V-waves normalized to the M-wave, and voluntary activation (twitch interpolation) would be reduced during plantar flexor maximum voluntary isometric contraction and that the evoked muscle twitch properties would be reduced in the paretic limb. Ten chronic stroke survivors completed the study. The main findings were that the paretic side showed deteriorated function compared to the non-paretic leg in terms of (1) RFD in all analyzed time windows from force onset to 250 ms, although relative RFD (i.e. normalized to maximum voluntary force) was similar; (2) fast neural activation (for most analyzed time windows), assessed by EMG activity in time windows from EMG onset to 250 ms; (3) V-wave responses (except for gastrocnemius medialis); (4) voluntary activation; (5) the evoked peak twitch force, although there was no evidence of intrinsic muscle slowing; (6) EMG activity obtained at maximal voluntary force. In conclusion, this study demonstrates considerable neuromuscular asymmetry of the plantar flexors in chronic stroke survivors. Effective rehabilitation regimes should be investigated.
PMCID: PMC3218282  PMID: 21455614
H-reflex; Neural drive; Brain infarction; Cerebrovascular accident; Rehabilitation
21.  Effects of unilateral robotic limb loading on gait characteristics in subjects with chronic stroke 
Hemiparesis after stroke often leads to impaired ankle motor control that impacts gait function. In recent studies, robotic devices have been developed to address this impairment. While capable of imparting forces to assist during training and gait, these devices add mass to the paretic leg which might encumber patients' gait pattern. The purpose of this study was to assess the effects of the added mass of one of these robots, the MIT's Anklebot, while unpowered, on gait of chronic stroke survivors during overground and treadmill walking.
Nine chronic stroke survivors walked overground and on a treadmill with and without the anklebot mounted on the paretic leg. Gait parameters, interlimb symmetry, and joint kinematics were collected for the four conditions. Repeated-measures analysis of variance (ANOVA) tests were conducted to examine for possible differences across four conditions for the paretic and nonparetic leg.
The added inertia and friction of the unpowered anklebot had no statistically significant effect on spatio-temporal parameters of gait, including paretic and nonparetic step time and stance percentage, in both overground and treadmill conditions. Noteworthy, interlimb symmetry as characterized by relative stance duration was greater on the treadmill than overground regardless of loading conditions. The presence of the unpowered robot loading reduced the nonparetic knee peak flexion on the treadmill and paretic peak dorsiflexion overground (p < 0.05).
Our results suggest that for these subjects the added inertia and friction of this backdriveable robot did not significantly alter their gait pattern.
PMCID: PMC2887457  PMID: 20492698
22.  Loss of independent limb control in childhood hemiparesis is related to time of brain injury onset 
This study investigated the presence of inter-limb activity at the elbow joint in individuals with childhood-onset hemiparesis, including spontaneous mirror movements during unilateral tasks and the ability to suppress them during bilateral tasks.
Eighteen individuals with hemiparesis were divided into three categories of injury timing: before birth (PRE-natal), around the time of birth (PERI-natal), and after 6 months of age (POST-natal). Individuals with hemiparesis, as well as 12 typically developing peers, participated in unilateral and bilateral elbow flexion and extension tasks completed at maximal and submaximal effort while muscle activity was monitored and motor output was quantified by two multiple degrees-of-freedom load cells.
Significantly higher levels of paretic elbow flexion were found only in the PRE- and PERI-natal groups during the flexion of the non-paretic limb, which was modulated by effort level in both unilateral and bilateral tasks.
The bilateral activation of elbow flexors in the PRE-/PERI-natal groups indicates potential use of a common cortical command source to drive both upper extremities, while the POST-natal/typically developing groups’ flexors appear to receive input from different supraspinal structures.
PMCID: PMC3679902  PMID: 23411673
cerebral palsy; childhood hemiparesis; mirror movements; childhood hemiplegia; arm coordination
23.  Saturated muscle activation contributes to compensatory reaching strategies following stroke 
Journal of neurophysiology  2005;94(5):2999-3008.
The control and execution of movement could potentially be altered by the presence of stroke-induced weakness if muscles are incapable of generating sufficient power. The purpose of this study was to identify compensatory strategies during a forward (sagittal) reaching task for twenty persons with chronic stroke and ten healthy age-matched controls. We hypothesized that the paretic anterior deltoid would be maximally activated (i.e., saturated) during a reaching task and that task completion would require activation of additional muscles, resulting in compensatory movements out of the sagittal plane. For reaching movements by control subjects, joint motion remained largely in the sagittal plane and hand trajectories were smooth and direct. Movement characteristics of the non-paretic arm of stroke subjects were similar to control subjects except for small increases in the abduction angle and the percentage that anterior deltoid was activated. In contrast, reaching movements of the paretic arm of stroke subjects were characterized by increased activation of all muscles, especially the lateral deltoid, in addition to the anterior deltoid, with resulting shoulder abduction power and segmented and indirect hand motion. For the paretic arm of stroke subjects, muscle and kinetic compensations increased with impairment severity and weaker muscles were used at a higher percentage of their available muscle activity. These results suggest that the inability to generate sufficient force with the typical agonists involved during a forward reaching task may necessitate compensatory muscle recruitment strategies to complete the task.
PMCID: PMC3471982  PMID: 16014786 CAMSID: cams2416
Upper extremity; arm; motor control; biomechanics; EMG; rehabilitation
24.  Factors predicting weight-bearing asymmetry 1 month after unilateral total knee arthroplasty: a cross-sectional study 
Gait & posture  2012;37(3):363-367.
Factors predicting weight-bearing asymmetry (WBA) after unilateral total knee arthroplasty (TKA) are not known. However, identifying modifiable and non-modifiable predictors of WBA is needed to optimize rehabilitation, especially since WBA is negatively correlated to poor functional performance. The purpose of this study was to identify factors predictive of WBA during sit-stand transitions for people 1 month following unilateral TKA.
Fifty-nine people were tested preoperatively and 1 month following unilateral TKA for WBA using average vertical ground reaction force under each foot during the Five Times Sit to Stand Test. Candidate variables tested in the regression analysis represented physical impairments (strength, muscle activation, pain, and motion), demographics, anthropometrics, and movement compensations.
WBA, measured as the ratio of surgical/non-surgical limb vertical ground reaction force, was 0.69 (0.18) (mean (SD)) 1 month after TKA. Regression analysis identified preoperative WBA (β = 0.40), quadriceps strength ratio (β = 0.31), and hamstrings strength ratio (β = 0.19) as factors predictive of WBA 1 month after TKA (R2 = 0.30).
Greater amounts of WBA 1 month after TKA are predicted by modifiable factors including habitual movement pattern and asymmetry in quadriceps and hamstrings strength.
PMCID: PMC3529981  PMID: 22980137
Total Knee Arthroplasty; Movement Asymmetry; Rehabilitation
25.  Spectral Analyses of Wrist Motion in Individuals Poststroke: The Development of a Performance Measure With Promise for Unsupervised Settings 
Upper extremity use in daily life is a critical ingredient of continued functional recovery after cerebral stroke. However, time-evolutions of use-dependent motion quality are poorly understood due to limitations of existing measurement tools.
Proof-of-concept study to determine if spectral analyses explain the variability of known temporal kinematic movement quality (ie, movement duration, number of peaks, jerk) for uncontrolled reach-to-grasp tasks.
Ten individuals with chronic stroke performed unimanual goal-directed movements using both hands, with and without task object present, wearing accelerometers on each wrist. Temporal and spectral measures were extracted for each gesture. The effects of performance condition on outcome measures were determined using 2-way, within subject, hand (nonparetic vs paretic) × object (present vs absent) analysis of variance. Regression analyses determined if spectral measures explained the variability of the temporal measures.
There were main effects of hand on all 3 temporal measures and main effects of object on movement duration and peaks. For the paretic limb, spectral measures explain 41.2% and 51.1% of the variability in movement duration and peaks, respectively. For the nonparetic limb, spectral measures explain 40.1%, 42.5%, and 27.8% of the variability of movement duration, peaks, and jerk, respectively.
Spectral measures explain the variability of motion efficiency and control in individuals with stroke. Signal power from 1.0 to 2.0 Hz is sensitive to changes in hand and object. Analyzing the evolution of this measure in ambient environments may provide as yet uncharted information useful for evaluating long-term recovery.
PMCID: PMC3900236  PMID: 24213957
stroke rehabilitation; hemiplegia; kinematics; upper extremity; accelerometry; motion sensing

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