Denis Gravel

Plantarflexor weakness as a limiting factor of gait speed in stroke subjects and the compensating role of hip flexors

OBJECTIVE To determine, using the Muscular Utilization Ratio (MUR) method, whether plantarflexor weakness is among the factors preventing stroke subjects from walking at faster speeds. Potential compensations by the hip flexors were also examined. DESIGN A convenience sample of 17 chronic stroke subjects in a context of a descriptive study. BACKGROUND Gait speed is correlated with the residual strength of the muscles involved in gait in stroke subjects. However, it has not been established if this residual strength limits gait speed. METHODS Kinetic and kinematic data for comfortable and maximal gait speeds were collected on the paretic side, and were used to determine the moments in plantarflexion (mechanical demand: MUR numerator) during the push-off phase. The maximal potential moment (MUR denominator) of the plantarflexors during gait was predicted using an equation derived from dynamometric data collected with a Biodex system. The MURs of the plantarflexors were then calculated at every 1% interval of the push-off phase. The pull-off phase of gait and the hip flexor strength were also examined. RESULTS Ten subjects of the sample had a MUR value between 80 and 150% at maximal gait speed. These subjects produced the lowest peak torques in plantarflexion. Each of the four fastest subjects of this group had a large hip flexion moment during the pull-off phase of gait and produced high hip flexion torque values on the dynamometer. Each of the seven remaining subjects had a MUR value under 70% when they walked at maximal speed. CONCLUSIONS Weakness of the plantarflexors should be considered as one factor limiting gait speed in 10 hemiparetic subjects. Some subjects with weak plantarflexors could walk rapidly because they compensated with the hip flexors. For the remaining stroke subjects, factors other than weakness of the plantarflexors have to be considered in order to explain the reduction in their gait speed.

Maximal grip force in chronic stroke subjects and its relationship to global upper extremity function

Objectives: Previous studies have shown that recovery of recordable grip strength in acute stroke subjects is one of the most sensitive assessments of initial upper limb recovery and a good prognostic factor for latter recovery. The objectives of this study were to test the reliability of maximal voluntary grip force (MVGF) measures and evaluate the relationship between paretic grip strength deficit and paretic upper extremity function in chronic stroke subjects. Design: Over a three-week period, bilateral MVGF was assessed three times with a modified strain gauge dynamometer in 15 chronic stroke subjects and 10 control subjects. The paretic MVGF deficit was expressed in relation to the MVGF of the nonaffected hand. Outcome measures: Upper extremity function in stroke subjects was measured using the Fugl-Meyer, the upper extremity performance test for the elderly (TEMPA), Box and Block and finger-to-nose tests. Results: MVGF measures in both groups of subjects demonstrated good reliability (intraclass correlation, ICC >0.86) and low standard error measurements (SEM). The paretic MVGF of the stroke subjects was greatly impaired in comparison to the control subjects. Results of linear and quadratic regressions analyses show that this impairment was significantly correlated (p <0.01) with the performance of the stroke subjects on the four upper extremity function tests. The percentages of variances explained by the MVGF deficit on all four upper extremity tests varied from 62% to 78% for the linear regressions and from 72% to 93% for the quadratic regressions. Conclusions: These results suggest that the paretic maximal grip strength, normalized with the maximal grip strength on the nonaffected side, appears to be a valuable outcome measure of upper extremity function in chronic stroke subjects.

Analysis of the clinical factors determining natural and maximal gait speeds in adults with a stroke.

The objective of this study was to identify the most important clinical variables determining gait speed in persons with stroke. Sixteen chronic stroke subjects (mean age, 47.9 (+/-15.6) yr; mean time post-stroke, 43.9 (+/-36.5) mo) able to walk independently without a brace participated in the study. The impairments in motor function, sensation of the paretic lower limb, and balance were evaluated with the Fugl-Meyer Assessment. A spasticity index was used to assess the muscle tone of the plantarflexors. The maximal strengths in plantarflexion and hip flexion were measured with a Biodex dynamometric system. Cinematography and foot-contact data collected on the paretic side were used to determine the comfortable and maximal gait speeds. The level of association between gait speeds and the clinical variables were first examined with Pearsons correlation coefficients and, then, with multiple linear regression analyses using the stepwise method. Results revealed that the motor function of the lower limb, balance, and hip flexion strength were significantly related to comfortable and maximal gait speeds (0.5 < r < 0.88; P < 0.05). For the comfortable gait speed, the regression analysis selected only the hip flexor strength as a significant variable (R2 = 0.69). For maximal gait speed, the variables retained were hip flexor strength, sensation at the lower limb, and plantarflexor strength (R2 = 0.85). The present results suggest that strength and sensation at the lower limb are important factors to consider in determining the gait capacity of chronic stroke subjects.

Evaluation of measurement strategies to increase the reliability of EMG indices to assess back muscle fatigue and recovery

The purpose of this study was to assess different measurement strategies to increase the reliability of different electromyographic (EMG) indices developed for the assessment of back muscle impairments. Forty male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three sessions at least 2 days apart within 2 weeks. Surface EMG signals were recorded from four pairs (bilaterally) of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10) while the subjects performed, in a static dynamometer, two static trunk extension tasks at 75% of the maximal voluntary contraction separated by a 60 s rest period: (1) a 30 s fatigue task and (2) a 5 s recovery task. Different EMG indices (based on individual muscles or averaged across bilateral homologous muscles or across all muscles) were computed to evaluate muscular fatigue and recovery. Intra-class correlation coefficient (ICC) and standard error of measurement (SEM) in percentage of the grand mean were calculated for each EMG variable. Reliable EMG indices are achieved for both healthy and chronic low back pain subjects when (1) electrodes are positioned on medial back muscles (multifidus at the L5 level and longissimus at L1) and (2) measures are averaged across bilateral muscles and/or across two fatigue tests performed within a session. The most reliable EMG indices were the bilateral average of medial back muscles (ICC range: 0.68-0.91; SEM range: 5-35%) and the average of all back muscles (ICC range: 0.77-0.91; SEM range: 5-30%). The averaging of measures across two fatigue tests is predicted to increase the reliability by about 13%. With regards to EMG indices of fatigue, the identification of the most fatigable muscle also lead to satisfactory results (ICC range: 0.74-0.79; SEM range: 21-26%). The assessment of back muscle impairments through EMG analysis necessitates the use of multiple electrodes to achieve reliable results.

The influence of an increase in the level of force on the EMG power spectrum of elbow extensors

SummaryIt has been proposed that the mean power frequency (MPF) of the electromyogram (EMG) power spectrum increases gradually with force of contraction and that this increase is a function of the fiber-type content of the muscle investigated and the inter-electrode distance (IED) used when recording the EMG signals. In order to test these hypotheses, the values of the MPF of two elbow extensor muscles, triceps brachii (TB, 65% fast twitch fibers) and anconeus (AN, 65% slow twitch fibers), were compared at different levels of contraction. Subjects (n =13) produced ten static ramp elbow extensions [0–100% maximum voluntary contraction (MVC)]. EMG signals of each muscle were recorded with two pairs of surface miniature electrodes having IEDs of 6 mm and 30 mm respectively. MPFs were obtained at each of the following levels: 10, 20, 40, 60, 80 and 100% MVC. Statistical analyses indicated that the MPF of AN increased significantly (P<0.05) up to 60% MVC. In contrast, the MPF values for TB showed no significant change across different levels of contraction (P>0.05). Since skinfold was on average 3.2 times thicker over TB than over AN it is suggested that the low-pass filtering effect of the skin could have prevented the observation of an increase of the MPF for TB. It thus appears that changes of the MPF with the level of force, as disclosed by surface electrode recordings, is specific to each muscle. Consequently one has to account for factors such as thickness of the skinfold when it comes to the determination of the fiber-type content of different muscles within a subject.

Normality and stationarity of EMG signals of elbow flexor muscles during ramp and step isometric contractions

The purpose of this study was to test the stationarity and normality of electromyographic (EMG) signals obtained while exerting isometric contractions: (a) where a steady force level is maintained (step contractions); and (b) where the force level is increased linearly over time (ramp contractions). Ramp elbow flexions were performed from 0 to 100% of the maximum voluntary contraction (MVC) in a 5-s period. For the step contractions, four force levels (20, 40, 60 and 80% MVC) were maintained for a period of 3 s each. EMG signals of the biceps brachii (BB) and brachioradialis (BR) muscles of 16 subjects were recorded with surface electrodes and digitized at a sampling frequency of 2000 Hz. Tests of normality (Shapiro-Wilk test) and stationarity (reverse arrangement test) were performed locally on short finite time records (512-ms windows). Results show that, in general, EMG signals present a non-Gaussian amplitude distribution and are stationary. Furthermore, the amplitude distribution characteristics and the stationarity of the signal were not dependent on the muscle investigated, nor on the type of contraction or force level tested. The finding of local stationarity for both tasks is important, because it suggests that performing standard spectral analysis is applicable for both step and ramp contractions. It also allows a direct comparison between results obtained under both conditions.

Surface electromyography assessment of back muscle intrinsic properties

The purpose of this study was to assess (1) the reliability and (2) the sensitivity to low back pain status and gender of different EMG indices developed for the assessment of back muscle weakness, muscle fiber composition and fatigability. Healthy subjects (men and women) and chronic low back pain patients (men only) performed, in a static dynamometer, maximal and submaximal static trunk extension tasks (short and long duration) to assess weakness, fiber composition and fatigue. Surface EMG signals were recorded from four (bilateral) pairs of back muscles and three pairs of abdominal muscles. To assess reliability of the different EMG parameters, 40 male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three occasions. Reliable EMG indices were achieved for both healthy and chronic low back pain subjects when specific measurement strategies were applied. The EMG parameters used to quantify weakness and fiber composition were insensitive to low back status and gender. The EMG fatigue parameters did not detect differences between genders but unexpectedly, healthy men showed higher fatigability than back pain patients. This result was attributed to the smaller absolute load that was attributed to the patients, a load that was defined relative to their maximal strength, a problematic measure with this population. An attempt was made to predict maximal back strength from anthropometric measurements but this prediction was prone to errors. The main difficulties and some potential solutions related to the assessment of back muscle intrinsic properties were discussed.

Physiotherapy for persistent postnatal stress urinary incontinence: a randomized controlled trial.

OBJECTIVE: The aim of this study was to compare the effectiveness of multimodal supervised physiotherapy programs with the absence of treatment among women with persistent postnatal stress urinary incontinence. METHODS: This was a single-blind randomized controlled trial. Sixty-four women with stress urinary incontinence were randomly assigned to 8 weeks of either multimodal pelvic floor rehabilitation (n = 21), multimodal pelvic floor rehabilitation with abdominal muscle training (n = 23), or control non–pelvic floor rehabilitation (n = 20). The primary outcome measure consisted of a modified 20-minute pad test. The secondary outcome measures included a Visual Analog Scale describing the perceived burden of incontinence, the Urogenital Distress Inventory, the Incontinence Impact Questionnaire, and pelvic floor muscle function measurements. RESULTS: Two patients dropped out, leaving 62 for analysis. At follow-up, more than 70% of the women in the treatment groups (14/20 in the pelvic floor and 17/23 in the pelvic floor plus abdominal group) were continent on pad testing compared with 0% of women in the control group. Scores on the pad test, Visual Analog Scale, Urogenital Distress Inventory, and Incontinence Impact Questionnaire improved significantly in both treatment groups (all P < .002), whereas no changes were observed in the control group. Pelvic floor muscle function, however, did not improve significantly in either active group. CONCLUSION: Multimodal supervised pelvic floor physiotherapy is an effective treatment for persistent postnatal stress urinary incontinence. LEVEL OF EVIDENCE: I

Gait study of patients with patellofemoral pain syndrome

Patellofemoral pain syndrome is a frequent knee impairment in young adults. This study investigated the kinematic and kinetic gait patterns of individuals suffering from patellofemoral pain syndrome (PFPS). It was hypothesized that PFPS subjects modify their gait pattern in order to reduce loading on the painful patellofemoral joint. To verify this, the gait pattern of five subjects with right chronic PFPS was compared with that of five healthy subjects. Spatiotemporal, kinematic and kinetic data were collected from five gait cycles. The joint moments at the hip, knee and ankle joints were calculated using an inverse dynamic approach and the values were normalized to body weight (N·m/kg). Individual joint moments were expressed as a percentage of the support moment in order to quantify possible compensatory strategies. The kinematic analysis revealed a significant reduction of the knee flexion angle (ANOVAs, P 0.05) as far as the individual joint moments and their contribution to the support moment were concerned. However, modifications were observed in the knee and hip moments between 10% and 20% of the gait cycle. These modifications may suggest that PFPS subjects alter their gait pattern in order to reduce loading of the patellofemoral joint to avoid pain.

EMG power spectra of elbow extensors during ramp and step isometric contractions

SummaryThe goal of the present study was to compare electromyogram (EMG) power spectra obtained from step (constant force level) and ramp (progressive increase in the force level) isometric contractions. Data windows of different durations were also analysed for the step contractions, in order to evaluate the stability of EMG power spectrum statistics. Fourteen normal subjects performed (1) five ramp elbow extensions ranging from 0 to 100% of the maximum voluntary contraction (MVC) and (2) three stepwise elbow extensions maintained at five different levels of MVC. Spectral analysis of surface EMG signals obtained from triceps brachii and anconeus was performed. The mean power frequency (MPF) and the median frequency (MF) of each power spectrum were obtained from 256-ms windows taken at 10, 20, 40, 60 and 80% MVC for each type of contraction and in addition on 512-, 1024-and 2048-ms windows for the step contractions. No significant differences (P>0.05) were found in the values of both spectral statistics between the different window lengths. Even though no significant differences (P>0.05) were found between the ramp and the step contractions, significant interactions (P<0.05) between these two types of contraction and the force level were found for both the MPF and the MF data. These interactions point out the existence of different behaviours for both the MPF and the MF across force levels between the two types of contraction.