Respiratory Mechanical and Cardiorespiratory Consequences of Cycling with Aerobars

PURPOSE

Aerobars place a cyclist in a position where the trunk is flexed forward and the elbows are close to the midline of the body. This position is known to improve cycling aerodynamics and time trial race performance compared with upright cycling positions. However, the aggressive nature of this position may have important cardiorespiratory and metabolic consequences. The purpose of this investigation was to examine the respiratory mechanical, ventilatory, metabolic, and sensory consequences of cycling while using aerobars during laboratory-based cycling.

METHODS

Eleven endurance-trained male cyclists (age, 26 ± 9 yr; V˙O2peak, 55 ± 5 mL·kg·min) were recruited. Visit 1 consisted of an incremental cycling test to determine peak power output. Visit 2 consisted of 6-min bouts of constant load cycling at 70% of peak incremental power output in the aerobar position, drop position, and upright position while grasping the brake hoods. Metabolic and ventilatory responses were measured using a commercially available metabolic cart, and respiratory pressures were measured using an esophageal catheter.

RESULTS

Cycling in the aerobar position significantly increased the work of breathing (Wb), power of breathing (Pb), minute ventilation, ventilatory equivalent for oxygen and carbon dioxide, and transdiaphragmatic pressure compared with the upright position. Increases in the Wb and Pb in the aerobars relative to the upright position were strongly correlated with the degree of thoracic restriction, measured as the shoulder-to-aerobar width ratio (Wb: r = 0.80, P = 0.01; Pb: r = 0.69, P = 0.04).

CONCLUSIONS

Aerobars significantly increase the mechanical cost of breathing and leads to greater ventilatory inefficiency compared with upright cycling. Future work is needed to optimize aerobar width to minimize the respiratory mechanical consequences while optimizing aerodynamics.

A Pre-Operative Exercise Intervention Can Be Safely Delivered to People with Femoroacetabular Impingement and Improve Clinical and Biomechanical Outcomes

Purpose: This study aimed to investigate the effects of a pre-hip arthroscopy exercise intervention on hip strength, pain, and function in individuals with femoroacetabular impingement (FAI). Methods: A total of 20 individuals with FAI completed a 10-week, partially supervised exercise programme; this included three phases of increasing resistance and functionality, consisting of four to six exercises per phase. Hip strength in all six directions; hip pain; function, as measured by the Hip disability and Osteoarthritis Outcome Score (HOOS); and objective physical function, as measured by the Timed Stair Climb test, were determined before and after the intervention. Results: Maximum isometric hip strength significantly increased in abduction (p=0.008), adduction (p=0.021), and internal rotation (p=0.006) at follow-up. Increases in flexion, extension, and external rotation strength did not reach statistical significance. Self-reported HOOS pain (p<0.01) and activities of daily living sub-scale scores (p<0.01) significantly improved at follow-up. Timed Stair Climb times (p<0.001) also significantly decreased at follow-up. Conclusion: A 10-week exercise programme can be safely completed by adults with FAI before surgery, and statistically significant changes in strength, function, and self-reported clinical outcomes can be achieved.

Validation of a smart shoe for estimating foot progression angle during walking gait

The foot progression angle is an important measurement related to knee loading, pain, and function for individuals with knee osteoarthritis, however current measurement methods require camera-based motion capture or floor-embedded force plates confining foot progression angle assessment to facilities with specialized equipment. This paper presents the validation of a customized smart shoe for estimating foot progression angle during walking. The smart shoe is composed of an electronic module with inertial and magnetometer sensing inserted into the sole of a standard walking shoe. The smart shoe charges wirelessly, and up to 160h of continuous data (sampled at 100Hz) can be stored locally on the shoe. For validation testing, fourteen healthy subjects were recruited and performed treadmill walking trials with small, medium, and large toe-in (internal foot rotation), small, medium, and large toe-out (external foot rotation) and normal foot progression angle at self-selected walking speeds. Foot progression angle calculations from the smart shoe were compared with measurements from a standard motion capture system. In general, foot progression angle values from the smart shoe closely followed motion capture values for all walking conditions with an overall average error of 0.1±1.9deg and an overall average absolute error of 1.7±1.0deg. There were no significant differences in foot progression angle accuracy across the seven different walking gait patterns. The presented smart shoe could potentially be used for knee osteoarthritis or other clinical applications requiring foot progression angle assessment in community settings or in clinics without specialized motion capture equipment.

The effects of shoe-worn insoles on gait biomechanics in people with knee osteoarthritis: a systematic review and meta-analysis

OBJECTIVES

The effect of shoe-worn insoles on biomechanical variables in people with medial knee osteoarthritis has been studied extensively. The majority of research has focused specifically on the effect of lateral wedge insoles at the knee. The aim of this systematic review and meta-analysis was to summarise the known effects of different shoe-worn insoles on all biomechanical variables during level walking in this patient population to date.

METHODS

Four electronic databases were searched to identify studies containing biomechanical data using shoe-worn insole devices in the knee osteoarthritis population. Methodological quality was assessed and a random effects meta-analysis was performed on biomechanical variables reported in three or more studies for each insole.

RESULTS

Twenty-seven studies of moderate-to-high methodological quality were included in this review. The primary findings were consistent reductions in the knee adduction moment with lateral wedge insoles, although increases in ankle eversion with these insoles were also found.

CONCLUSION

Lateral wedge insoles produce small reductions in knee adduction angles and external moments, and moderate increases in ankle eversion. The addition of an arch support to a lateral wedge minimises ankle eversion change, and also minimises adduction moment reductions. The paucity of available data on other insole types and other biomechanical outcomes presents an opportunity for future research.

Lateral wedges with and without custom arch support for people with medial knee osteoarthritis and pronated feet: an exploratory randomized crossover study

BACKGROUND

Pronated foot posture is associated with many clinical and biomechanical outcomes unique to medial compartment knee osteoarthritis (OA). Though shoe-worn insole treatment, including lateral wedges, is commonly studied in this patient population, their effects on the specific subgroup of people with medial knee OA and concomitant pronated feet are unknown. The purpose of this study was to evaluate whether lateral wedge insoles with custom arch support are more beneficial than lateral wedge insoles alone for knee and foot symptoms in people with medial tibiofemoral knee osteoarthritis (OA) and pronated feet.

METHODS

Twenty-six people with pronated feet and symptomatic medial knee OA participated in a randomized crossover study comparing five degree lateral wedge foot insoles with and without custom foot arch support. Each intervention was worn for two months, separated by a two-month washout period of no insoles wear. Main outcomes included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and physical function subscales, the revised short-form Foot Function Index (FFI-R) pain and stiffness subscales, and the timed stair climb test. Regression modeling was conducted to examine treatment, period, and interaction effects.

RESULTS

Twenty-two participants completed the study, and no carryover or interaction effects were observed for any outcome. Significant treatment effects were observed for the timed stair climb, with greater improvements seen with the lateral wedges with arch support. Within-condition significant improvements were observed for WOMAC pain and physical function, as well as FFI-R pain and stiffness with lateral wedges with arch support use. More adverse effects were reported with the lateral wedges alone, while more people preferred the lateral wedges with arch support overall.

CONCLUSIONS

Addition of custom arch support to a standard lateral wedge insole may improve foot and knee symptoms in people with knee OA and concomitant pronated feet. These preliminary findings suggest further research evaluating the role of shoe-worn insoles for treatment of this specific sub-group of people with knee OA is warranted.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT02234895.

Physiological arousal accompanying postural responses to external perturbations after stroke

OBJECTIVE

The purpose of this study was to examine simultaneously the level of physiological arousal and the postural response to external perturbations in people post-stroke compared to age-matched controls to build a more comprehensive understanding of the effect of stroke on postural control and balance self-efficacy.

METHODS

Participants stood with each foot on separate force platforms. Ten applications of loads of 2% body weight at the hips perturbed the participant anteriorly under two conditions: investigator-triggered or self-triggered (total 20). Electrodermal activity (EDA; measurement of physiological arousal), electromyography (EMG) of the ankle plantarflexor muscles and anterior-posterior center of pressure measurements were taken pre-perturbation (anticipatory) and post-perturbation (response) and compared between the initial (first two) and final (last two) perturbations.

RESULTS

Participants post-stroke demonstrated significantly higher levels of anticipatory EDA and anticipatory paretic plantarflexor EMG during both self- and investigator-triggered conditions compared to controls. Anticipatory EDA levels were higher in the final perturbations in participants post-stroke in both conditions, but not in controls. Habituation of the EDA responses post-perturbation was exhibited in the self-triggered perturbations in controls, but not in participants post-stroke.

CONCLUSIONS

Physiological arousal and postural control strategies of controls revealed habituation in response to self-triggered perturbations, whereas this was not seen in participants post-stroke.

SIGNIFICANCE

Understanding the physiological arousal response to challenges to standing balance post-stroke furthers our understanding of postural control mechanisms post-stroke.

Dynamic Balance Training Improves Physical Function in Individuals With Knee Osteoarthritis: A Pilot Randomized Controlled Trial

OBJECTIVE

To examine the effect of a targeted balance training program on dynamic balance and self-reported physical function in people with medial tibiofemoral osteoarthritis (OA).

DESIGN

Single-blind randomized controlled trial.

SETTING

Exercise gymnasium and community dwellings.

PARTICIPANTS

Individuals with medial compartment knee OA (N=40).

INTERVENTIONS

Ten weeks of partially supervised exercises targeting dynamic balance and strength performed 4 times per week or no intervention (nonintervention group).

MAIN OUTCOME MEASURES

Dynamic balance was measured using the Community Balance and Mobility Scale (CB&M), and self-reported physical function was measured using the Western Ontario and McMaster Universities Arthritis Index physical function subscale. Secondary outcomes included knee pain, fear of movement, knee joint proprioception, and muscle strength.

RESULTS

Forty individuals underwent baseline testing, with 36 participants completing follow-up testing. Adherence to exercise in the training group was high, with 82.2% of all home-based exercise sessions completed. No significant changes were observed in any outcome in the nonintervention group at follow-up. Significant improvements in self-reported pain, physical function, and fear of movement were observed in the training group when compared with the nonintervention group. No other within- or between-group differences were observed.

CONCLUSIONS

A 10-week dynamic balance training program for people with knee OA significantly improved self-reported knee pain, physical function, and fear of movement; however, there was no change in dynamic balance as quantified by the CB&M. Further research is needed to investigate how exercise may result in improvement on objective measures of dynamic balance.

Trunk and lower limb biomechanics during stair climbing in people with and without symptomatic femoroacetabular impingement

BACKGROUND

Femoroacetabular impingement is a pathomechanical hip condition leading to pain and impaired physical function. It has been shown that those with femoroacetabular impingement exhibit altered gait characteristics during level walking and stair climbing, and decreased muscle force production during isometric muscle contractions. However, no studies to-date have looked at trunk kinematics or muscle activation during dynamic movements such as stair climbing in this patient population. The purpose of this study was to compare biomechanical outcomes (trunk and lower limb kinematics as well as lower limb kinetics and muscle activation) during stair climbing in those with and without symptomatic femoroacetabular impingement.

METHODS

Trunk, hip, knee and ankle kinematics, as well as hip, knee and ankle kinetics and muscle activity of nine lower limb muscles were collected during stair climbing for 20 people with clinical and radiographic femoroacetabular impingement and compared to 20 age- and sex-matched pain-free individuals.

FINDINGS

Those with femoroacetabular impingement ascended the stairs slower (effect size=0.82), had significantly increased peak trunk forward flexion angles (effect size=0.99) and external hip flexion moments (effect size=0.94) and had decreased peak external knee flexion moments (effect size=0.90) compared to the control group.

INTERPRETATION

Findings from this study indicate that while those with and without femoroacetabular impingement exhibit many biomechanical similarities when ascending stairs, differences in trunk forward flexion and joint kinetics indicate some important differences. Further longitudinal research is required to elucidate the cause of these differences as well as the clinical relevance.

Comorbidities That Cause Pain and the Contributors to Pain in Individuals With Chronic Obstructive Pulmonary Disease

OBJECTIVE

To determine comorbidities that cause pain and the potential contributors to pain in individuals with chronic obstructive pulmonary disease (COPD).

DESIGN

Prospective cross-sectional survey study.

SETTING

Pulmonary rehabilitation programs of 6 centers.

PARTICIPANTS

A convenience sample of individuals with COPD (N=137) who attended pulmonary rehabilitation programs. In total, 100 (73%) returned the survey packages. Of those responders, 96 participants (70%) were included in the analyses.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Pain was measured using the Brief Pain Inventory. The questionnaire used to obtain information about health conditions that might contribute to pain and a medication record asked, in lay terms, about comorbidities that cause pain. The health conditions that cause pain were then validated by health professionals. Demographics, fatigue, dyspnea, quality of life, and self-efficacy were also measured using questionnaires.

RESULTS

Pain was reported in 71% (68/96) of participants. Low back pain was the most common location (41%). Arthritis (75%), back problems (47%), and muscle cramps (46%) were the most common comorbidities that caused pain. Lower self-efficacy, and renting rather than home ownership increased the likelihood of pain (P<.05). Pain severity and Brief Fatigue Inventory scores contributed to pain interference scores (P<.05).

CONCLUSIONS

Pain was highly prevalent in pulmonary rehabilitation program participants with COPD. The most common causes of pain were musculoskeletal conditions. Pain severity and higher levels of fatigue contributed to how pain interfered with daily aspects of living. The assessment and management of pain need to be addressed within the overall care of individuals with COPD.

Knee and ankle biomechanics with lateral wedges with and without a custom arch support in those with medial knee osteoarthritis and flat feet

This study compared immediate changes in knee and ankle/subtalar biomechanics with lateral wedge orthotics with and without custom arch support in people with knee osteoarthritis and flat feet. Twenty-six participants with radiographic evidence of medial knee osteoarthritis (22 females; age 64.0 years [SD 8.0 years], BMI 27.2 kg/m(2) [4.2]) and flat feet (median foot posture index = + 5) underwent three-dimensional gait analysis for three conditions: Control (no orthotic), lateral wedge, and lateral wedge plus arch support. Condition order was randomized. Outcomes included frontal plane knee and ankle/subtalar biomechanics, and comfort. Compared to the control, lateral wedge and lateral wedge with arch support reduced the knee adduction moment impulse by 8% and 6%, respectively (p < 0.05). However, the lateral wedge resulted in a more everted foot position (4.3 degrees) than lateral wedge plus arch support (3.2 degrees) (p < 0.05). In contrast, lateral wedge plus arch support reduced foot frontal plane excursion compared to other conditions (p < 0.05). Participants self-reported significantly more immediate comfort with lateral wedge plus arch support compared to the control, whereas there was no difference in self-reported comfort between lateral wedge and control. No immediate changes in knee pain were observed in any condition.

CLINICAL SIGNIFICANCE

Rather than prescribing lateral wedges to all patients with knee osteoarthritis, those who have medial knee osteoarthritis and flat feet may prefer to use the combined orthotic to reduce loads across the knee, and to minimize the risk of foot and ankle symptoms as a consequence of orthotic treatment. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1597-1605, 2016.

Influence of Biomechanical Characteristics on Pain and Function Outcomes From Exercise in Medial Knee Osteoarthritis and Varus Malalignment: Exploratory Analyses From a Randomized Controlled Trial

OBJECTIVE

To investigate whether selected biomechanical characteristics influence changes in pain and physical function with exercise in people with medial knee osteoarthritis (OA) and varus malalignment.

METHODS

We conducted post hoc exploratory analyses from a randomized controlled trial involving 100 people with medial knee OA and varus malalignment who were randomly allocated to one of two 12-week exercise programs (quadriceps strengthening [QS] or neuromuscular exercise [NEXA]). The outcome measures were change in overall average knee pain (visual analog scale) and self-reported physical function (Western Ontario and McMaster Universities Osteoarthritis Index). Candidate biomechanical characteristics measured at baseline were visually observed varus thrust during walking, obesity (determined by body mass index), static varus alignment, and isometric quadriceps strength. Data were analyzed with separate two-way analyses of covariance using the interaction term of exercise group by biomechanical characteristic.

RESULTS

Ninety-two participants were analyzed for each characteristic except varus thrust, for which 85 participants were included. For change in pain, there was a significant interaction effect between type of exercise and both varus thrust (P = 0.001) and obesity (P = 0.023). NEXA was more effective for nonobese participants (mean change 29.5 mm [95% confidence interval (95% CI) 20.5, 38.5]) and for those with varus thrust (mean change 28.7 mm [95% CI 19.4, 38.1]), whereas QS was more effective for obese people (mean change 24.7 mm [95% CI 14.9, 34.4]) and for those without varus thrust (mean change 29.4 mm [95% CI 21.2, 37.7]). Biomechanical characteristics did not influence the effect of exercise on physical function (P > 0.05).

CONCLUSION

These preliminary findings suggest that varus thrust and obesity influence the pain-relieving effects of 2 different types of exercise. Further research is needed to confirm whether or not exercise that is prescribed according to specific biomechanical characteristics optimizes knee OA outcomes.

Immediate Effects of a Brace on Gait Biomechanics for Predominant Lateral Knee Osteoarthritis and Valgus Malalignment After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Lateral knee osteoarthritis is notably common after anterior cruciate ligament reconstruction (ACLR). While valgus bracing has been investigated as an intervention for medial knee osteoarthritis (OA), little is known about the effectiveness of varus bracing for lateral knee OA after ACLR.

PURPOSE

To determine the immediate effects of a varus unloader knee brace on gait biomechanics in people with lateral knee OA and valgus malalignment after ACLR.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nineteen participants who had undergone primary ACLR 5 to 20 years previously and had symptomatic and radiographic lateral knee OA as well as valgus malalignment were included. Three-dimensional gait analyses were conducted during walking under 3 test conditions: (1) no brace, (2) unadjusted brace (sagittal plane support with neutral frontal plane adjustment), and (3) adjusted brace (sagittal plane support with varus adjustment). Knee, pelvis, hip, and ankle kinematics and moments data were statistically analyzed using repeated-measures analysis of variance (α = 0.05).

RESULTS

Compared with walking with no brace, the adjusted brace significantly increased peak knee flexion angle (mean difference [95% CI]: 3.2° [1.3° to 5.0°]) and adduction angle (1.7° [0.8° to 2.6°]) and reduced peak internal rotation angle (-3.0° [-4.0° to -2.0°]). Significant increases in peak knee flexion moment (0.14 N·m/kg [0.06 to 0.20 N·m/kg]), adduction moment (0.10 N·m/kg [0.07 to 0.14 N·m/kg]), and external rotation moment (0.01 N·m/kg [0.00 to 0.02 N·m/kg]) were observed with the adjusted brace. The adjusted brace also reduced peak hip adduction angle (-1.29° [-2.12 to -0.47]) and increased peak hip adduction (0.17 N·m/kg [0.04 to 0.31 N·m/kg]) and external rotation moments (0.09 N·m/kg [0.03 to 0.14 N·m/kg]). There were no significant differences between the adjusted and unadjusted brace conditions, except for knee internal rotation angle, where the adjusted brace produced significantly greater reductions relative to the unadjusted brace (-1.46° [-1.98 to -0.95]).

CONCLUSION

Irrespective of frontal plane adjustment, the varus unloader brace produced immediate modulations in sagittal, frontal, and transverse plane joint angles and moments in younger individuals with lateral knee OA and valgus malalignment after ACLR.

CLINICAL RELEVANCE

The varus unloader brace may have the potential to mitigate abnormal knee joint mechanics associated with the development and progression of lateral knee OA after ACLR.

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.

PARTICIPANTS

Individuals (n=27) in the subacute phase after stroke and healthy controls (n=8) (N=35).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Timing (onset and offset) and normalized amplitude (percent electromyography maximum) of the biceps femoris (BF) and rectus femoris (RF) muscles were measured during terminal swing and early stance. A co-contraction index (CCI) was calculated for the BF and RF muscle activity. Individuals with CCI values equal to or below the mean of the healthy group were in the low CCI group, whereas those with values above the mean were in the high CCI group. Functional balance and mobility evaluation used the Community Balance and Mobility Scale (CB&M).

RESULTS

For the paretic and nonparetic limbs, measures of timing, amplitude, and co-contraction were similar for both limbs. Compared with the healthy group, the high CCI group had lower CB&M scores, longer durations, and higher levels of RF and BF muscle activity, whereas the low CCI group had electromyographic measures statistically similar to healthy controls.

CONCLUSIONS

The motor control of gait after subacute stroke is characterized by symmetry of timing and amplitude of muscle recruitment at the knee. High co-contraction levels surrounding the knee were associated with lower functional balance and mobility. These findings suggest a compensatory strategy of increased co-contraction in those with more impairment while maintaining symmetry of lower-limb biomechanics between limbs.

Gait modifications to change lower extremity gait biomechanics in runners: a systematic review

BACKGROUND

Abnormal biomechanics have been cited as a potential risk factor for running-related injury. Many modifiable biomechanical risk factors have also been proposed in the literature as interventions via gait retraining.

AIM

To determine which interventions have successfully modified biomechanical variables linked to running-related injury.

STUDY DESIGN

Systematic literature review.

METHODS

MEDLINE, EMBASE, CINAHL, SportDiscus and PSYCINFO were searched using key terms related to running biomechanics and gait retraining. Quality of included studies was assessed using the modified Downs and Black Quality Index and a best evidence synthesis was performed.

RESULTS

27 studies investigating the effect of biomechanical interventions on kinetic, kinematic and spatiotemporal variables were included in this review. Foot strike manipulation had the greatest effect on kinematic measures (conflicting evidence for proximal joint angles; strong evidence for distal joint angles), real-time feedback had the greatest effect on kinetic measures (ranging from conflicting to strong evidence), and combined training protocols had the greatest effect on spatiotemporal measures (limited to moderate evidence).

CONCLUSIONS

Overall, this systematic review shows that many biomechanical parameters can be altered by running modification training programmes. These interventions result in short term small to large effects on kinetic, kinematic and spatiotemporal outcomes during running. In general, runners tend to employ a distal strategy of gait modification unless given specific cues. The most effective strategy for reducing high-risk factors for running-related injury-such as impact loading-was through real-time feedback of kinetics and/or kinematics.

Laboratory-based measurement of standing balance in individuals with knee osteoarthritis: a systematic review

BACKGROUND

Laboratory-based measurement of standing balance is used to assess postural control in people with and without pathology, including knee osteoarthritis. However, no summary of available data has been reported in this patient population. This study aimed to summarize available data and testing methods for individuals with knee osteoarthritis.

METHODS

Medline (OvidSP and PubMed), Embase, CINAHL, and Web of Science were searched from 1994 to October 25, 2014 to identify studies containing a quantifiable measure of standing balance. Methodological quality was assessed using a modified 17-item Downs & Black quality index. Studies scoring <50% were eliminated.

FINDINGS

The search strategy initially yielded 1523 unique papers; 21 met all inclusion and quality assessment criteria. The variables measured in three or more of the 21 papers were anteroposterior centre of pressure (COP) velocity, mediolateral COP velocity, mean COP velocity, anteroposterior range of COP, mediolateral range of COP, anteroposterior COP standard deviation, mediolateral COP standard deviation, COP path length, COP area, Biodex anteroposterior score, Biodex mediolateral score, and overall Biodex score. In general, people with knee osteoarthritis exhibited worse standing balance compared to healthy controls. However, there remained much discrepancy in testing procedures across studies.

INTERPRETATION

These findings indicate that people with knee osteoarthritis exhibit altered postural control. However, no conclusions could be made on the differences between radiographic severities. That said, these findings provide an opportunity for future researchers and clinicians to compare their findings with the currently published data.

Behavior of medial gastrocnemius motor units during postural reactions to external perturbations after stroke

OBJECTIVE

This study investigated the behavior of medial gastrocnemius (GM) motor units (MU) during external perturbations in standing in people with chronic stroke.

METHODS

GM MUs were recorded in standing while anteriorly-directed perturbations were introduced by applying loads of 1% body mass (BM) at the pelvis every 25-40s until 5% BM was maintained. Joint kinematics, surface electromyography (EMG), and force platform measurements were assessed.

RESULTS

Although external loads caused a forward progression of the anterior-posterior centre of pressure (APCOP), people with stroke decreased APCOP velocity and centre of mass (COM) velocity immediately following the highest perturbations, thereby limiting movement velocity in response to perturbations. MU firing rate did not increase with loading but the GM EMG magnitude increased, reflecting MU recruitment. MU inter spike interval (ISI) during the dynamic response was negatively correlated with COM velocity and hip angular velocity.

CONCLUSIONS

The GM utilized primarily MU recruitment to maintain standing during external perturbations. The lack of MU firing rate modulation occurred with a change in postural central set. However, the relationship of MU firing rate with kinematic variables suggests underlying long-loop responses may be somewhat intact after stroke.

SIGNIFICANCE

People with stroke demonstrate alterations in postural control strategies which may explain MU behavior with external perturbations.