Physiological Responses to Spinal Manipulation Therapy: Investigation of the Relationship Between Electromyographic Responses and Peak Force

Objective

It is believed that systematic modulation of spinal manipulative therapy (SMT) parameters should yield varying levels of physiological responses and eventually a range of clinical responses. However, investigation of SMT dose–physiological response relationship is recent and has mostly been conducted using animal or cadaveric models. The main objective of the present study is to investigate SMT dose–physiological response relation in humans by determining how different levels of force can modify electromyographic (EMG) responses to spinal manipulation.

Methods

Twenty-six participants were subjected to 2 trials of 4 different SMT force-time profiles using a servo-controlled linear actuator motor. Normalized EMG activity of paraspinal muscles (left and right muscles at level T6 and T8) was recorded during and after SMT, and EMG values were compared across the varying levels of force.

Results

Increasing the level of force yielded an increase in paraspinal muscle EMG activity during the thrust phase of SMT but also in the two 250-millisecond time windows after the spinal manipulation impulse. These muscle activations quickly attenuated (500 milliseconds after spinal manipulation impulse).

Conclusion

The study confirmed the presence of a local paraspinal EMG response after SMT and highlighted the linear relationship between the SMT peak force and paraspinal muscle activation.     

Creation of an asymmetrical gradient of back muscle activity and spinal stiffness during asymmetrical hip extension

Background

Low back pain is often associated with increased spinal stiffness which thought to arise from increased muscle activity. Unfortunately, the association between paraspinal muscle activity and paraspinal stiffness, as well as the spatial distribution of this relation, is unknown. The purpose of this investigation was to employ new technological developments to determine the relation between spinal muscle contraction and spinal stiffness over a large region of the lumbar spine.

Methods

Thirty-two male subjects performed graded isometric prone right hip extension at four different exertion levels (0%, 10%, 25% and 50% of the maximum voluntary contraction) to induce asymmetric back muscle activity. The corresponding stiffness and muscle activity over bilateral paraspinal lumbar regions was measured by indentation loading and topography surface electromyography, respectively. Paraspinal stiffness and muscle activity were then plotted and their correlation was determined.

Findings

Data from this study demonstrated the existence of an asymmetrical gradient in muscle activation and paraspinal stiffness in the lumbar spine during isometric prone right hip extension. The magnitude and scale of the gradient increased with the contraction force. A positive correlation between paraspinal stiffness and paraspinal muscle activity existed irrespective of the hip extension effort (Pearson correlation coefficient, range 0.566–0.782 (P < 0.001)).

Interpretation

Our results demonstrate the creation of an asymmetrical gradient of muscle activity and paraspinal stiffness during right hip extension. Future studies will determine if alterations in this gradient may possess diagnostic or prognostic value for patients with low back pain.     

A comparison of ultrasound and electromyography measures of force and activation to examine the mechanics of abdominal wall contraction

Background

Ultrasound imaging is a valuable tool which, when applied appropriately, has the potential to provide information regarding the mechanics of abdominal muscle contraction. Typically, changes in muscle thickness are obtained and interpreted. However, the link between ultrasound measures of muscle thickening and EMG measures of activation is not clear.

Methods

Five healthy males performed a series of abdominal muscle contractions while surface EMG and trunk posture were monitored and ultrasound images of the internal oblique and external oblique were captured both at relaxation and upon contraction. Ramped isometric flexor and extensor moment contractions were also assessed and compared between EMG and ultrasound.

Findings

No definitive relationship between increases in muscle activation and corresponding measures of thickening was observed. Correlations between the two measures, across all contraction types, were 0.14 for internal oblique and −0.22 for external oblique.

Interpretation

The lack of clear association between abdominal muscle activation and thickening may be due to the composite laminate-like structure of the abdominal wall, with force being transmitted between obliquely oriented muscle layers. Thus, ultrasound alone may not be a valid measure of muscle activation or force in the unique architecture of the abdominal wall.     

Back extensor muscle fatigue at submaximal workloads assessed using frequency banding of the electromyographic signal

Background

Changes in the mean or median frequency of the electromyographic (EMG) power spectrum are often used to assess skeletal muscle fatigue. A more global analysis of the spectral changes using frequency banding may provide a more sensitive measure of fatigue than changes in mean or median frequency. So, the aim of the present study was to characterize changes in different power spectrum frequency bands and compare these with changes in median frequency.

Methods

Twenty male subjects performed isometric contractions of the back muscles in an isometric dynamometer at 30%, 40%, 50% and 60% of maximum voluntary contraction. During each contraction, surface EMG signals were recorded from the right and left longissimus thoracis muscles, and endurance time was measured. The EMG power spectra were divided into four frequency bands (20–50 Hz; 50–80 Hz; 80–110 Hz; 110–140 Hz) and changes in power in each band with fatigue were compared with changes in median frequency.

Findings

The percentage changes in 20–50 Hz band were greater than in all other and the rate of change in power, indicated by the slope, was also greatest in 20–50 Hz band. Also, 20–50 Hz band had a greater change in power than the median frequency.

Interpretation

Power in the low frequency part of the EMG power spectrum increases with fatigue in a load-dependent manner. The rate of change in low frequency power may be a useful indicator of fatigue rate or “fatigability” in the back muscles. Also, changes in low frequency power are more evident than changes in the median frequency.     

Effects of tactile feedback on lumbar multifidus muscle activity in asymptomatic healthy adults and patients with low back pain

Background

Reduced lumbar multifidus (LM) muscle contraction has been observed in patients with low back pain (LBP). Clinicians often use various strategies to ensure LM activation, including tactile feedback and verbal instruction. However, the effects of tactile feedback on muscle activation have not been studied previously. Therefore, the purpose of this study was to investigate whether or not tactile feedback would increase LM muscle activity in adults with and without LBP.

Trunk Neuromuscular Responses to a Single Whole-Body Vibration Session in Patients With Chronic Low Back Pain: A Cross-Sectional Study

Objective

Whole-body vibration (WBV) exercise is progressively adopted as an alternative therapeutic modality for enhancing muscle force and muscle activity via neurogenic potentiation. So far, possible changes in the recruitment patterns of the trunk musculature after WBV remain undetermined. The main objective of this study was to evaluate the short-term effects of a single WBV session on trunk neuromuscular responses in patients with chronic low back pain (cLBP) and healthy participants.

Methods

Twenty patients with cLBP and 21 healthy participants performed 10 trunk flexion-extensions before and after a single WBV session consisting of five 1-minute vibration sets. Surface electromyography (EMG) of erector spinae at L2-L3 and L4-L5 and lumbopelvic kinematic variables were collected during the trials. Data were analyzed using 2-way mixed analysis of variance models.

Results

The WBV session led to increased lumbar EMG activity during the flexion and extension phases but yielded no change in the quiet standing and fully flexed phases. Kinematic data showed a decreased contribution to the movement of the lumbar region in the second extension quartile. These effects were not different between patients with cLBP and healthy participants.

Conclusions

Increased lumbar EMG activity after a single WBV session most probably results from potentiation effects of WBV on lumbar muscles reflex responses. Decreased EMG activity in full trunk flexion, usually observed in healthy individuals, was still present after WBV, suggesting that the ability of the spine stabilizing mechanisms to transfer the extension torque from muscles to passive structures was not affected.     

Effects of hip extensor fatigue on lower extremity kinematics during a jump-landing task in women: A controlled laboratory study

Background

Lower extremity kinematics may change as a result of impaired hip muscle function, thereby placing athletes at increased risk of injury. The purpose of this study was to examine whether experimentally-induced hip extensor fatigue alters lower extremity kinematics during a jump-landing task in women.

Methods

Forty healthy women were randomly assigned to an experimental group in which participants performed modified Biering-Sørenson tests to fatigue the hip extensors or to a sham control group in which participants performed repeated push-ups to exhaustion. Three-dimensional hip and knee kinematics and gluteus maximus electromyography (EMG) signals were measured during jump-landing tests to examine the effects of hip extensor fatigue.

Findings

Hip extension strength decreased in the experimental group by 25% following the intervention, thereby confirming effects of the fatigue intervention. No group × time interactions in hip and knee motions were statistically significant, indicating that hip and knee kinematics did not change following the fatigue-inducing intervention. Gluteus maximus recruitment during the post-fatigue test, however, increased by 55% in the experimental group.

Interpretation

A 25% reduction in hip extensor strength did not lead to changes in hip or knee kinematics. Rather, participants accommodated for the loss of strength by recruiting more Gmax activation to complete the task. Gmax recruitment may compensate when hip extensor strength is impaired, suggesting that improved neuromuscular control can influence motor performance when strength is diminished.     

Insertion and Presence of Fine-Wire Intramuscular Electrodes to the Lumbar Paraspinal Muscles Do Not Affect Muscle Performance and Activation During High-Exertion Spinal Extension Activities

Background

Low back pain (LBP) is commonly associated with paraspinal muscle dysfunctions. A method to study deep lumbar paraspinal (ie, multifidus) muscle function and neuromuscular activation pattern is intramuscular electromyography (EMG). Previous studies have shown that the procedure does not significantly impact muscle function during activities involving low-level muscle contractions. However, it is currently unknown how muscular function and activation are affected during high-exertion contractions.

Use of a geared wheelchair wheel to reduce propulsive muscular demand during ramp ascent: Analysis of muscle activation and kinematics

Background

Shoulder muscle overuse has been linked to the high prevalence of shoulder injuries in manual wheelchair users. Ramp ascent is a barrier that is often faced by manual wheelchair users that requires higher muscle activations than level wheelchair propulsion. Additionally, reported subjective measures of shoulder pain are reduced amongst manual wheelchair users when using a wheelchair wheel outfitted with a gear mechanism. The purpose of the current investigation was to investigate shoulder muscle activation levels and upper limb kinematics during ramp ascent with and without the use of a geared wheel.

Methods

Thirteen healthy participants (6 male and 7 female) performed ramp ascent on four ramp grades (1:12, 1:10, 1:8, 1:6) using three wheel conditions (gear, no gear, standard). Electromyographic (EMG) activity of select shoulder muscles as well as kinematics of the right upper limb were collected during ramp ascent. Peak and integrated EMG as well as peak wrist, elbow, and shoulder kinematics were obtained from all ramp ascent trials.

Findings

Peak EMG of the shoulder flexors decreased by an average of 17% (P ? 0.0229) during ramp ascent with the geared wheel. Integrated EMG increased by 67% (P ? 0.0034) as a consequence of an 86% increase (P = 0.0009) in ramp ascent duration during the geared wheel condition. There were no significant differences between the non-geared and standard wheel conditions.

Interpretation

Caution must be used if using the gear ratio for prolonged periods due to potential for muscle fatigue since the overall muscle effort to move a fixed distance is higher with the gear ratio. Reducing peak demands may benefit wheelchair users with performing more strenuous tasks of daily living.     

Incorporating ultrasound-measured musculotendon parameters to subject-specific EMG-driven model to simulate voluntary elbow flexion for persons after stroke

Background

This study was to extend previous neuromusculoskeletal modeling efforts through combining the in vivo ultrasound-measured musculotendon parameters on persons after stroke.

Method

A subject-specific neuromusculoskeletal model of the elbow was developed to predict the individual muscle force during dynamic movement and then validated by joint trajectory. The model combined a geometrical model and a Hill-type musculotendon model, and used subject-specific musculotendon parameters as inputs. EMG signals and joint angle were recorded from healthy control subjects (n = 4) and persons after stroke (n = 4) during voluntary elbow flexion in a vertical plane. Ultrasonography was employed to measure the muscle optimal length and pennation angle of each prime elbow flexor (biceps brachii, brachialis, brachioradialis) and extensor (three heads of triceps brachii). Maximum isometric muscle stresses of the flexor and extensor muscle group were calibrated by minimizing the root mean square difference between the predicted and measured maximum isometric torque–angle curves. These parameters were then inputted into the neuromusculoskeletal model to predict the individual muscle force using the input of EMG signals directly without any trajectory fitting procedure involved.

Findings

The results showed that the prediction of voluntary flexion in the hemiparetic group using subject-specific parameters data was better than that using cadaveric data extracted from the literature.

Interpretation

The results demonstrated the feasibility of using EMG-driven neuromusculoskeletal modeling with direct ultrasound measurement for the prediction of voluntary elbow movement for both subjects without impairment and persons after stroke.     

Transient analysis of trunk response in sudden release loading using kinematics-driven finite element model

Background

Sudden trunk perturbations occur in various occupational and sport activities. Despite numerous measurement studies, no comprehensive modeling simulations have yet been attempted to investigate trunk biodynamics under sudden loading/unloading.

Methods

Dynamic kinematics-driven approach was used to evaluate the temporal variation of trunk muscle forces, internal loads and stability before and after a sudden release of a posterior horizontal load. Measured post-disturbance trunk kinematics, as input, and muscle electromyography (EMG) activities, for qualitative validation, were considered.

Findings

Computed agonist and antagonist muscle forces before and after release agreed well with reported EMG activities and demonstrated basic response characteristics such as activation latency and reflex activation. The trunk was found quite stable before release and in early post-release period. Larger applied load substantially increased trunk kinematics, muscle forces and spinal loads.

Interpretation

Excessive spinal loads due to large muscle forces in sudden loading conditions is a risk factor as the central nervous system attempts to reflexively control the sudden disturbances, a situation that further deteriorates under larger perturbations and longer latency periods. Predictions indicate the potential of the kinematics-driven model in ergonomics as well as training and rehabilitation programs.     

The Role of Preload Forces in Spinal Manipulation: Experimental Investigation of Kinematic and Electromyographic Responses in Healthy Adults

Objectives

Previous studies have identified preload forces and an important feature of skillful execution of spinal manipulative therapy (SMT) as performed by manual therapists (eg, doctors of chiropractic and osteopathy). It has been suggested that applying a gradual force before the thrust increases the spinal unit stiffness, minimizing displacement during the thrust. Therefore, the main objective of this study was to assess the vertebral unit biomechanical and neuromuscular responses to a graded increase of preload forces.

Methods

Twenty-three participants underwent 4 different SMT force-time profiles delivered by a servo-controlled linear actuator motor and varying in their preload forces, respectively, set to 5, 50, 95, and 140 N in 1 experimental session. Kinematic markers were place on T6, T7, and T8 and electromyographic electrodes were applied over paraspinal muscles on both sides of the spine.

Results

Increasing preload forces led to an increase in neuromuscular responses of thoracic paraspinal muscles and vertebral segmental displacements during the preload phase of SMT. Increasing the preload force also yielded a significant decrease in sagittal vertebral displacement and paraspinal muscle activity during and immediately after the thrust phase of spinal manipulation. Changes observed during the SMT thrust phase could be explained by the proportional increase in preload force or the related changes in rate of force application. Although only healthy participants were tested in this study, preload forces may be an important parameter underlying SMT mechanism of action. Future studies should investigate the clinical implications of varying SMT dosages.

Conclusion

The present results suggest that neuromuscular and biomechanical responses to SMT may be modulated by preload through changes in the rate of force application. Overall, the present results suggest that preload and rate of force application may be important parameters underlying SMT mechanism of action.     

Morphology Versus Function: The Relationship Between Lumbar Multifidus Intramuscular Adipose Tissue and Muscle Function Among Patients With Low Back Pain

Objective

To explore the bivariate and multivariate relations between fatty degeneration of the lumbar multifidus muscle (LMM) and LMM function among patients with low back pain (LBP).

Design

Cross-sectional clinical study.

Setting

Hospital.

Participants

Patients with LBP (N=70) referred for lumbar spine magnetic resonance imaging.

Interventions

Not applicable.

Main Outcome Measures

LMM morphology and function were measured at the L4/L5 and L5/S1 spinal levels bilaterally. Quantitative measures of LMM intramuscular adipose tissue (IMAT) were derived from T1-weighted magnetic resonance images. Function was assessed with ultrasound imaging by measuring change in LMM thickness during a submaximal contraction task. The study participants self-reported their level of LBP-related disability (Modified Oswestry Index), pain intensity (numerical pain rating scale), and physical activity (International Physical Activity Questionnaire). Bivariate and multivariate relations between LMM morphology and function were explored with correlational and hierarchical linear regression analyses, respectively. Additionally, we explored for possible covariates with potential to modify the relation between LMM IMAT and function.

Results

There were 70 participants (12 women) enrolled in the study (mean age, 45.4±11.9y). A high level of physical activity was reported by 45.5% of participates. Age, sex, and physical activity level demonstrated variable relations with LMM IMAT and LMM function. There were no significant bivariate or multivariate relations between LMM IMAT and LMM function.

Conclusions

We observed higher levels of physical activity and LMM function and less LMM IMAT than previous studies involving patients with LBP. There was no relation between LMM morphology and function in this cohort of patients with LBP. Issues specific to LMM measurement and recommendations for future research are discussed.     

Fatigability of back extensor muscles and low back pain during pregnancy

Background

Back pain is the most frequently reported musculo-skeletal problem during pregnancy. High muscle fatigability has been associated with back pain in the general population. During pregnancy, the gradual increase in loads may have a training effect, increasing strength and endurance of back muscles. This adaptation however may be too slow, or insufficient to be significant in light of other changes during pregnancy.

Methods

Thirty-two pregnant women performed a fatigue test which consisted of maintaining a fixed load of 70 Nm for 60 s while the surface EMG of the longissimus lumborum and multifidus muscles were recorded bilaterally at 14, 24 and 34 weeks of pregnancy. The measure of fatigability was the highest absolute slope of the median frequency of the power spectrum of the EMG of the four muscles. Occurrence and severity of back pain were reported on questionnaires at 14, 19, 24, 29 and 34 weeks. Binomial logistic regressions between back pain occurrence and the median frequency slopes were calculated.

Findings

None of the five logistic analyses demonstrated an improvement of the one-predictor model over the constant-only model, which indicates that the degree of fatigability of back extensor muscles did not predict the occurrence of back pain in our sample.

Interpretation

Fatigability of back extensor muscles was not found to be a predictor of back pain during pregnancy. This result should be taken with caution due to the small number of participants and broad definition of back pain used, and should be confirmed by studies with a larger number of participants.     

Females exhibit shorter paraspinal reflex latencies than males in response to sudden trunk flexion perturbations

Background

Females have a higher risk of experiencing low back pain or injury than males. One possible reason for this might be altered reflexes since longer paraspinal reflex latencies exist in injured patients versus healthy controls. Gender differences have been reported in paraspinal reflex latency, yet findings are inconsistent. The goal here was to investigate gender differences in paraspinal reflex latency, avoiding and accounting for potentially gender-confounding experimental factors.

Methods

Ten males and ten females underwent repeated trunk flexion perturbations. Paraspinal muscle activity and trunk kinematics were recorded to calculate reflex latency and maximum trunk flexion velocity. Two-way mixed model analyses of variance were used to determine the effects of gender on reflex latency and maximum trunk flexion velocity.

Findings

Reflex latency was 18.7% shorter in females than in males (P = 0.02) when exposed to identical trunk perturbations, and did not vary by impulse (P = 0.38). However, maximum trunk flexion velocity was 35.3% faster in females than males (P = 0.01) when exposed to identical trunk perturbations, and increased with impulse (P < 0.01). While controlling for differences in maximum trunk flexion velocity, reflex latency was 16.4% shorter in females than males (P = 0.04).

Interpretation

The higher prevalence of low back pain and injury among females does not appear to result from slower paraspinal reflexes.     

Preliminary evidence for the features of non-reducible discogenic low back pain: survey of an international physiotherapy expert panel with the Delphi technique

Objectives

The lumbar intervertebral disc is a known source of low back pain (LBP). Various clinical features of discogenic pain have been proposed, but none have been validated. Several subgroups of discogenic pain have been hypothesised, with non-reducible discogenic pain (NRDP) proposed as a relevant clinical subgroup. The objectives of this study were to obtain consensus from an expert panel on the features of discogenic low back pain, the existence of subgroups of discogenic LBP, particularly NRDP, and the associated features of NRDP.

Design

Three-round Delphi survey.

Participants

Twenty-one international physiotherapists with expertise in LBP.

Methods

Panellists listed and ranked features that they believed to be indicative of discogenic pain and NRDP. On completion of Round 3, features with ≥50% agreement between panellists were deemed to have reached consensus.

Results

After three rounds, 10 features of discogenic LBP were identified. Nineteen of the panellists believed that NRDP was a subgroup of discogenic LBP, and nine features of NRDP were identified.

Conclusion

This study provides preliminary validation for the features associated with discogenic LBP. It also provides evidence supporting the existence and features of NRDP as a separate clinical subgroup of discogenic LBP.     

Effet du sens de pose du kinesio taping sur les épicondyliens

Objective

The aim of this study was to assess the effect of a kinesio taping^® strip on epicondylians’ muscle activity at rest, according to the way of laying (distoproximal or proximodistal).

Methods

A strip of kinesio taping^® was positioned on the forearm of 54 subjects, divided in two groups of 27 subjects according to the way of laying. The surface electromyographic activity (EMG) was recorded on the epicondylian muscles at rest, before and after laying the strip.

Results

In the distoproximal group, the EMG activity at rest was significantly lower with the kinesio taping^® strip than the activity without the strip (40.2 mV vs 53.6 mV; P = 0.0035). There wasn’t any significant effect of the strip in the proximodistal group.

Discussion

The distoproximal laying of the kinesio taping^® strip had a detoning effect on epicondylians’ EMG activity at rest. The proximodistal laying didn’t have any effects.     

Effects of eccentric exercise on trapezius electromyography during computer work with active and passive pauses

Background

The aim of this laboratory study was to investigate the effects of eccentric exercises on the trapezius muscle spatial electromyographic (EMG) activity during computer work with active and passive pauses.

Methods

Twelve healthy male subjects performed computer work with passive (relax) and active (30% maximum voluntary contraction of shoulder elevation) pauses given every 40 s over 2 days, before, immediately and 24 h after eccentric exercise. Surface EMG signals were recorded from four parts of the trapezius during computer work.

Findings

EMG amplitude during computer work decreased immediately after exercise (P < 0.05). In the clavicular and descending parts of the trapezius, the centroid of exposure variation analysis along the time axis was lower during computer work with active pauses compared with passive ones (P < 0.05). Further, lower values of relative rest time was observed during active pause (P < 0.05).

Interpretation

Eccentric exercises had a short term effect on muscle activation pattern during computer work, and decreased the muscle activity immediately after the exercises. The results of this study showed a more variable trapezius activity pattern and a lower trapezius rest with active pauses compared with passive pauses. Moreover, eccentric exercises resulted in a less variable activation pattern, decreasing the effect of active pauses.     

Emergency Department Management of Patients with ACE-inhibitor Angioedema

Background

Angiotensin-converting-enzyme inhibitors (ACEI) are one of the most prescribed medications worldwide. Angioedema is a well-recognized adverse effect of this class of medications, with a reported incidence of ACEI angioedema of up to 1.0%. Of importance to note, ACEI angioedema is a class effect and is not dose dependent. The primary goal of this literature search was to determine the appropriate Emergency Department management of patients with ACEI angioedema.

Methods

A MEDLINE literature search from January 1990 to August 2012 and limited to human studies written in English for articles with keywords of ACEI angioedema. Guideline statements and non-systematic reviews were excluded. Studies identified then underwent a structured review from which results could be evaluated.

Results

Five hundred sixty-two papers on ACEI angioedema were screened and 27 appropriate articles were rigorously reviewed in detail and recommendations given.

Conclusion

The literature search did not support any specific treatment protocol with a high level of evidence due to the limited—and limitations of the—available studies.     

Coordination of the non-paretic leg during hemiparetic gait: Expected and novel compensatory patterns

Background

Post-stroke hemiparesis is usually considered a unilateral motor control deficit of the paretic leg, while the non-paretic leg is assumed to compensate for paretic leg impairments and have minimal to no deficits. While the non-paretic leg electromyography (EMG) patterns are clearly altered, how the non-paretic leg acts to compensate remains to be established.

Methods

Kinesiological data were recorded from sixty individuals with chronic hemiparesis (age: 60.9, SD = 12.6 years, 21 females, 28 right hemiparetic, time since stroke: 4.5 years, SD 3.9 years), divided into three speed-based groups, and twenty similarly aged healthy individuals (age: 65.1, SD = 10.4 years, 15 females). All walked on an instrumented split-belt treadmill at their self-selected speed and control subjects also walked at slower speeds matching those of the persons with hemiparesis. We determined the differences in magnitude and timing of non-paretic EMG activity relative to healthy control subjects in four pre-defined regions of stance phase of the gait cycle.

Findings

Integrated EMG activity and EMG timing in the non-paretic leg were different in many muscles. Multiple compensatory patterns identified included: increased EMG output when the muscle was typically active in controls and novel compensatory EMG patterns that appeared to provide greater propulsion or support with little evidence of impaired motor performance.

Interpretation

Most novel compensations were made possible by altered kinematics of the paretic and non-paretic leg (i.e., early stance plantarflexor activity provided propulsion due to the decreased advancement of the non-paretic foot) while others (late single limb stance knee extensor and late stance hamstring activity) appeared to be available mechanisms for increasing propulsion.