Individual Muscle Activation Research Articles

Immediate effect of hip taping on balance and walking ability in cane-dependent ambulators with chronic stroke: a randomized controlled trial.

Previous studies showed that cane-dependent post-stroke ambulators have poor balance and gait performance. Adhesive taping on the hip may be used as a therapeutic modality for improving range of motion and muscle activity in individuals with stroke. The objective of this study was to investigate the immediate effect of the hip extensor and abductor taping on balance and walking ability in cane-dependent ambulators with chronic stroke. This study was a single-blinded, randomized controlled trial. Outpatients from a hospital rehabilitation department. Twenty-eight cane-dependent ambulators with chronic stroke were recruited. Participants were randomized into either the control group with sham tape (N.=14) or experimental group with non-elastic tape (N.=14). The Berg Balance Scale, gait speed, 6-minute walk test, and Fall Efficacy Scale were measured with and without taping. After taping, participants in the experimental group showed significant improvement in the Berg Balance Scale, gait speed, and 6-minute walk test. Furthermore, experimental group showed significant improvement in the Berg Balance Scale and 6-minute walk test compared with sham taping control group. Non-elastic tape could immediately improve balance, gait speed, and endurance in cane-dependent ambulators with chronic stroke. Non-elastic tape may be a useful adjunct to current rehabilitation strategies for individuals with chronic stroke.

Effect of increasing workload on knee extensor and flexor muscular activity during cycling as measured with intramuscular electromyography.

The purpose of this study was to describe the effect of increasing workload on individual thigh muscle activation during a 20 minute incremental cycling test. Intramuscular electromyographic signals were recorded from the knee extensors rectus femoris, vastus lateralis, vastus medialis and vastus intermedius and the knee flexors semimembranosus, semitendinosus, and the short and long heads of the biceps femoris during increasing workloads. Mean activation levels were compared over the whole pedaling cycle and the crank angles at which onset and offset of activation and peak activity occurred were identified for each muscle. These data were compared between three workloads. EMG activation level significantly increased (p<0.05) with increasing workload in the rectus femoris, vastus medialis, vastus lateralis, vastus intermedius, biceps femoris long head, semitendinosus and semimembranosus but not in the biceps femoris short head. A significant change in activation timing was found for the rectus femoris, vastus lateralis, vastus medialis and semitendinosus. Of the knee flexors only the short head of the biceps femoris had its peak activity during the upstroke phase at the two highest workloads indicating a unique contribution to knee flexion.

Customization of Synergy-Based FES for Post-Stroke Rehabilitation of Upper-Limb Motor Functions.

Functional Electrical Stimulation (FES) provides a promising technology for rehabilitation of upper-limb motor functions following stroke. It enables activation of individual muscles to assist restoration of impaired muscle synergies toward normal patterns. However, there lacks a systematic approach to optimize the FES stimulation patterns delivered to patients with stroke. Our preliminary work demonstrated that it is feasible to use muscle synergy patterns to guide the generation of FES patterns. Here, we present the methodology of customizing synergy-based FES using parameterized formulae with three strategies: weight-sensitive, variability-sensitive, and duration-sensitive. Each of them is comprised of two parameter sets, which represent different directions of parameter search. Two patients with ischemic stroke were recruited to participate in the preliminary test of these strategies. Preliminary results indicate that all strategies could increase the peak velocity in reaching movements, but only the "variability-sensitive" strategy restrained unwanted shoulder excursions. This pilot study demonstrates the feasibility to explore in the parameter space the directions, along which the clinical benefit of synergy-based FES can be tracked and continuously optimized.

Impact of different EMG normalisation methods on muscle activations and cocontraction index in adults with chronic post-stroke hemiparesis

EMG normalisation is a key step to draw definite conclusions on physiologically standardized data. In the absence of a consensus in scientific literature, recommendations would be useful for the choice of EMG normalisation method in patients, such as hemiparetics, who present atypical EMG patterns during motor behavior. The aim of this work was to compare muscle activations and cocontraction index (CCI) using different EMG normalisation methods during active elbow extension in healthy participants and patients with chronic post-stroke hemiparesis. Four adults with chronic post-stroke hemiparesis (Hemi) and five healthy participants (Co) were included. Elbow kinematics and EMG activity of elbow flexors and triceps brachii were recorded during active elbow extensions performed at spontaneous speed. EMG signal was normalised in reference to EMG activity recorded during isometric or isokinetic MVC. Normalised EMG during elbow extension was used to compute muscle activations and CCI, during the acceleration and deceleration phases. Friedman tests were performed with two factors (group and normalisation). No differences were found between normalisation methods neither for muscle activations and for the cocontraction index in Co and Hemi groups. Greater muscle activations were found in Hemi vs. Co (24.2 ± 13.4% vs. 4.3 ± 3% and 52.4 ± 33.2% vs. 6.2 ± 4.3% during acceleration and deceleration phase, respectively). Cocontraction index in acceleration phase was greater in Hemi vs. Co ( P < 0.05), and in Co between acceleration and decceleration phases ( P < 0.05) ( Fig. 1 ). Even if isokinetic MVC-based EMG normalisation accounts for the influence of angle- and velocity-torque relationships, our results on EMG activations and cocontraction index support the use of isometric instead of isokinetic MVC normalisation, and further suggest the need to take into account individual muscle activations to better understand differences in cocontraction between groups and phases.

Kinematics-based prediction of trunk muscle activity in response to multi-directional perturbations during sitting

Recent work suggests that functional electrical stimulation can be used to enhance dynamic trunk stability following spinal cord injury. In this context, knowledge of the relation between trunk kinematics and muscle activation in non-disabled individuals may assist in developing kinematics-based neuroprostheses. Our objective was therefore to predict the activation profiles of the major trunk muscles from trunk kinematics following multi-directional perturbations during sitting. Trunk motion and electromyograms (EMG) from ten major trunk muscles were acquired in twelve non-disabled, seated individuals who experienced a force of approximately 200 N applied to the trunk in eight horizontal directions. A linear, time-invariant model with feedback gains on angular trunk displacement, velocity, and acceleration was optimized to predict the EMG from trunk kinematics. For each muscle, only the three directions that produced the largest EMG response were considered. Our results indicate that the time course of the processed EMG was similar across muscles and directions and that the model accounted for 68–92% of the EMG variance. A combination of neural and biomechanical mechanisms associated with trunk control can explain the obtained model parameters. Future work will apply the gained insights in the design of movement-controlled neuroprostheses for facilitating trunk stability following spinal cord injury.

Effect of the head extension swallowing exercise on suprahyoid muscle activity in elderly individuals.

Aging causes motor function deterioration in the elderly population, which in turn can cause weakness in the muscles associated with swallowing. Swallowing-related problems in elderly individuals can be prevented or their symptoms can be improved with strengthening exercises for the muscles involved in swallowing. The existing strengthening exercises for the suprahyoid muscle have their limitations. Therefore, it is necessary to find another exercise that can be performed by individuals whose personal characteristics make it difficult for them to perform the existing exercises. In this study, we investigated the changes in suprahyoid muscle activation, tongue strength, and thickness of the suprahyoid muscle after 8 weeks of the head extension swallowing exercise (HESE). A total of 23 healthy elderly individuals participated in an 8-week exercise program (20 min/session, 2 times/week for 8 weeks). Suprahyoid muscle activation during effortful swallowing and the effortful-normal ratio were significantly increased at 8 weeks compared to the baseline values (p = 0.002, and 0.033, respectively). Tongue tip pressure, tongue base pressure, normal swallowing pressure, effortful swallowing pressure, and tongue tip endurance were significantly increased at 8 weeks compared with baseline (p = 0.014, 0.004, 0.046, 0.009, and 0.004, respectively). The thickness of the digastric muscle and that of the mylohyoid muscle were significantly increased at 8 weeks compared with baseline (p = 0.000 and 0.004, respectively). This study showed that HESE can be a good option for improving the suprahyoid muscle and tongue strength in the elderly population. Additionally, this exercise does not require any additional equipment and has the advantage of being able to be performed anytime and anywhere. A variety of exercise options tailored according to individual characteristics may be helpful in choosing the most appropriate exercise.

Differences in Hip Joint Biomechanics and Muscle Activation in Individuals With Femoroacetabular Impingement Compared With Healthy, Asymptomatic Individuals: Is Level-Ground Gait Analysis Enough?

Background:Femoroacetabular impingement (FAI) is a recognized cause of hip and groin pain and a significant factor in hip joint function during sport. Objective tests for understanding hip function are lacking in this population.Purpose:To determine whether biomechanical and electromyographic features of hip function during level-ground walking differ between a group diagnosed with FAI and those with no symptoms of FAI.Study Design:Controlled laboratory study.Methods:A total of 20 asymptomatic individuals and 20 individuals with FAI walked on a dual-belt instrumented treadmill at self-selected walking velocities. Sagittal and frontal plane joint motions, moments, and muscle activation for the gluteus medius, gluteus maximus, rectus femoris, and medial and lateral hamstrings were analyzed. Discrete measures were extracted from each biomechanical waveform, and principal component analysis was used to determine hip joint muscle activation and hip adduction moment patterns. Statistical significance was determined by use of Student t tests with Bonferroni adjustments for multiple comparisons (α = .05).Results:Individuals with FAI walked more slowly (P = .015) and had lower self-reported function (P < .001). No differences in muscle strength were found between the symptomatic and contralateral legs in the FAI group (P > .017), but those with FAI had lower strength in the knee extensors and flexors and the hip extensors, flexors, and adductors compared with the asymptomatic group (P < .017). Individuals with unilateral symptomatic FAI walked with similar biomechanical and hip muscle electromyographic results bilaterally. The only differences found were a greater amplitude of gluteus maximus activation in the FAI symptomatic leg compared with the asymptomatic group and greater medial hamstring activation than lateral hamstring activation in the FAI group in both limbs compared with the asymptomatic group.Conclusion:Individuals with FAI were generally deconditioned and reported significantly more functional limitations. No biomechanical differences existed between groups during level walking, yet hamstring and gluteus maximus activation differed when the symptomatic group was compared with the asymptomatic group.Clinical Relevance:The field lacks objective testing of hip joint function to understand implications of FAI for dynamic movements, particularly with applications to biomechanics and electromyography. Level walking was of limited value for understanding FAI hip function, and the development of a more challenging gait assessment is warranted.

Effects of Kinesiology Taping on Scapular Reposition Accuracy, Kinematics, and Muscle Activity in Athletes With Shoulder Impingement Syndrome: A Randomized Controlled Study.

Scapular proprioception is a key concern in managing shoulder impingement syndrome (SIS). However, no study has examined the effect of elastic taping on scapular proprioception performance. To investigate the immediate effect of kinesiology taping (KT) on scapular reposition accuracy, kinematics, and muscle activation in individuals with SIS. Randomized controlled study. Musculoskeletal laboratory, National Yang-Ming University, Taiwan. Thirty overhead athletes with SIS. KT or placebo taping over the upper and lower trapezius muscles. The primary outcome measures were scapular joint position sense, measured as the reposition errors, in the direction of scapular elevation and protraction. The secondary outcomes were scapular kinematics and muscle activity of the upper trapezius, lower trapezius, and serratus anterior during arm elevation in the scapular plane (scaption). Compared with placebo taping, KT significantly decreased the reposition errors of upward/downward rotation (P = .04) and anterior/posterior tilt (P = .04) during scapular protraction. KT also improved scapular kinematics (significant group by taping effect for posterior tilt, P = .03) during scaption. Kinesiology and placebo tapings had a similar effect on upper trapezius muscle activation (significant taping effect, P = .003) during scaption. Our study identified the positive effects of KT on scapular joint position sense and movement control. Future studies with a longer period of follow-up and clinical measurement might help to clarify the clinical effect and mechanisms of elastic taping in individuals with SIS.

Characteristics of Lower Leg Muscle Activity in Patients with Cerebral Palsy during Cycling on an Ergometer.

Purpose Cycling on ergometer is often part of rehabilitation programs for patients with cerebral palsy (CP). The present study analyzed activity patterns of individual lower leg muscle during active cycling on ergometer in patients with CP and compared them to similar recordings in healthy participants. Methods Electromyographic (EMG) recordings of lower leg muscle activity were collected from 14 adult patients and 10 adult healthy participants. Activity of the following muscles was recorded: Musculus tibialis anterior, Musculus gastrocnemius, Musculus rectus femoris, and Musculus biceps femoris. Besides qualitative analysis also quantitative analysis of individual muscle activity was performed by computing the coefficient of variation of EMG signal amplitude. Results More irregular EMG patterns were observed in patients in comparison to healthy participants: agonist-antagonist cocontractions were more frequent, muscle activity measured at specific points of the cycle path was more variable, and dynamic range of muscle activity along the cycle path was narrower in patients. Hypertonicity was also more frequent in patients. Conclusion Muscle activity patterns during cycling differed substantially across patients. It showed irregular nature and occasional sharp high peaks. Dynamic range was also narrower than in controls. Observations underline the need for individualized cycling training to optimize rehabilitation effects.

Use of the surface electromyography for a quantitative trend validation of estimated muscle forces

Surface EMG is a non-invasive measurement of an individual muscle activity and it can be used as the indirect form of a simulated muscle forces validation. The quantitative curves comparison has some potential, which has not been fully exploited yet [13]. The purpose of current study was to quantitatively compare muscle forces predicted using musculoskeletal models to measured surface electromyography signals. A metrics based on correlation and an electromechanical delay correction for a quantitative trend validation has been proposed.Kinematics of a normal gait was collected for three healthy subjects together with ground reaction forces and EMG signals of eight different muscles of both legs. Dynamic simulations have been performed for two models of differing complexity from OpenSim library (Gait2392 and Gait2354) [2,5,6], static optimization method and computed muscle control algorithm [20] have been used. It has been shown, that the level of force-EMG trend compliance, obtained for applied models and simulation techniques, is related rather to the selected muscle than to applied optimization criteria or technique. The contribution of analyzed muscles during gait has been predicted better by complex model than by simplified model. Moreover relationship between the body proportion of subject and the degree of correlation has been observed. Proposed metrics and obtained results can be the basis for further identification of cost functions, which could most closely describe motor control strategy.

The immediate effect of muscle release intervention on muscle activity and shoulder kinematics in patients with frozen shoulder: a cross-sectional, exploratory study

BackgroundContractile tissue plays an important role in mobility deficits in frozen shoulder (FS). However, no study has assessed the effect of the muscle release technique on the muscle activation and kinematics in individuals with FS. The purposes of this study were to assess the differences in shoulder muscle activity and kinematics between the FS and asymptomatic groups; and to determine the immediate effects of muscle release intervention in the FS group.MethodsTwenty patients with FS and 20 asymptomatic controls were recruited. The outcome measures included muscle activity of the upper and lower trapezius (UT and LT), infraspinatus (ISp), pectoralis major (PM), and teres major (TM), shoulder kinematics (humeral elevation, scapular posterior tilt (PT) and upward rotation (UR), shoulder mobility, and pain. Participants in the FS group received one-session of heat and manual muscle release. Measurements were obtained at baseline, and immediately after intervention. Multivariate analysis of variance was used for data analysis. The level of significance was set at α=0.05.ResultsCompared to the controls, the FS group revealed significantly decreased LT (difference =55.89%, P=0.001) and ISp muscle activity (difference =26.32%, P =0.043) during the scaption task, and increased PM activity (difference =6.31%, P =0.014) during the thumb to waist task. The FS group showed decreased humeral elevation, scapular PT, and UR (difference = 35.36°, 10.18°, 6.73° respectively, P <0.05). Muscle release intervention immediately decreased pain (VAS drop 1.7, P <0.001); improved muscle activity during scaption (UT: 12.68% increase, LT: 35.46% increase, P <0.05) and hand to neck (UT: 12.14% increase, LT: 34.04% increase, P <0.05) task; and increased peak humeral elevation and scapular PT during scaption (95.18°±15.83° to 98.24°±15.57°, P=0.034; 11.06°±3.94° to 14.36°±4.65°, P=0.002), and increased scapular PT during the hand to neck (9.47°±3.86° to 12.80°±8.33°, P=0.025) task. No statistical significance was found for other group comparisons or intervention effect.ConclusionPatients with FS presented with altered shoulder muscle activity and kinematics, and one-session of heat and manual muscle release showed beneficial effects on shoulder muscle performance, kinematics, mobility, and pain.Trial registrationRetrospectively registered on Jan 18, 2016 (ACTRN 12616000031460).

The effect of scanning technology and UPC placement on supermarket self‐checkout

Self‐checking services are offered in many supermarkets. In order to checkout efficiently, customers must locate and scan the Universal Product Code (UPC) of the items with relative ease. Otherwise, their preferences toward using the self‐checkout (SCO) stations may be negatively affected. The current literature has no focus on UPC location, and the scanning technology used effect on performance and preferences. The purpose of this study is to investigate the effect of these from an operational and ergonomic perspective. To that end, 2 UPC placement techniques (current and recommended placement) and 2 scanning technologies (bi‐optic and handheld scanners) were tested. The total scanning time, individual items scanning time, trunk posture, total number of wrong twists/flips, individual items wrong flips, muscle activities, and participants' subjective preferences were measured. The results revealed that total scanning time was significantly reduced when using bi‐optic scanner (F = 20.9, P &lt; 0.01). The recommended UPC placement led to a significant improvement on UPC anticipation for both scanning technologies (F = 16.8, P &lt; 0.01). Additionally, exposure to non‐neutral trunk posture(s) was shown to be significantly decreased in the bi‐optic condition (F = 10.4, P &lt; 0.01). Proper UPCs' placement and bi‐optic scanner can positively improve the efficiency and experience of the SCO.

Selective recurrent laryngeal nerve stimulation using a penetrating electrode array in the feline model.

Laryngeal muscles (LMs) are controlled by the recurrent laryngeal nerve (RLN), injury of which can result in vocal fold (VF) paralysis (VFP). We aimed to introduce a bioelectric approach to selective stimulation of LMs and graded muscle contraction responses. Acute experiments in cats. The study included six anesthetized cats. In four cats, a multichannel penetrating microelectrode array (MEA) was placed into an uninjured RLN. For RLN injury experiments, one cat received a standardized hemostat-crush injury, and one cat received a transection-reapproximation injury 4 months prior to testing. In each experiment, three LMs (thyroarytenoid, posterior cricoarytenoid, and cricothyroid muscles) were monitored with an electromyographic (EMG) nerve integrity monitoring system. Electrical current pulses were delivered to each stimulating channel individually. Elicited EMG voltage outputs were recorded for each muscle. Direct videolaryngoscopy was performed for visualization of VF movement. Stimulation through individual channels led to selective activation of restricted nerve populations, resulting in selective contraction of individual LMs. Increasing current levels resulted in rising EMG voltage responses. Typically, activation of individual muscles was successfully achieved via single placement of the MEA by selection of appropriate stimulation channels. VF abduction was predominantly observed on videolaryngoscopy. Nerve histology confirmed injury in cases of RLN crush and transection experiments. We demonstrated the ability of a penetrating MEA to selectively stimulate restricted fiber populations within the feline RLN and selectively elicit contractions of discrete LMs in both acute and injury-model experiments, suggesting a potential role for intraneural MEA implantation in VFP management. NA. Laryngoscope, 128:1606-1614, 2018.

Muscular Exposures During Standardized Two-Handed Maximal Pushing and Pulling Tasks

OCCUPATIONAL APPLICATIONS We found markedly different muscular exposures and external hand force-generating muscle efficiencies when individuals produce maximal pushing and pulling forces in several experimental conditions (e.g., 100 cm versus 150 cm handle height, horizontal verss vertical grip orientation). For the same task characteristics, females produced higher levels of muscle activation and higher ratios of normalized muscle activity to force, which were likely the result of differing anthropometry between sexes. Females thus appear to be at higher risk for muscular overload during push/pull tasks. Pulling at waist height and pushing at shoulder height are recommended when possible, for similar task conditions to those studied. The high prevalence of pushing and pulling tasks in occupational settings enables use of these findings, in concert with traditional strength-based ergonomics assessments, to help protect both males and females from potential musculoskeletal overload.TECHNICAL ABSTRACT Rationale: Pushing and pulling tasks are highly prevalent across occupational settings. Despite increased availability of push and pull strength data, scarce information exists regarding specific muscle-based exposures when performing these tasks in common work configurations, and how these exposures differ between males and females. Purpose: We evaluated the influence of sex and several workplace factors on surface electromyography (EMG)-based exposure estimates during standardized, symmetric, two-handed maximal voluntary isometric push and pull tasks. Methods: Individual muscle and mean EMG activations (i.e., bilaterally and total), as well as weighted EMG to normalized force ratios (wEMG/nForce), were evaluated for seven bilateral shoulder and trunk muscles, in eight experimental conditions. Workplace factors manipulated were exertion direction (push and pull), handle height (100 cm and 150 cm) and handle orientation (vertical and horizontal). Results: For the muscles studied, pushing resulted in nearly twice (∼1.82×) the muscle activation than pulling. Across individual muscles, the largest difference between heights existed bilaterally for the pectoralis major, with pushing at 100 cm resulting in approximately twice the EMG amplitude. When pulling, only the right triceps activity differed between heights (i.e., 40% higher when exerting at 100 cm). Females produced higher normalized muscle activations (i.e., 23% higher across all muscles), and were generally less efficient than males, as indicted by a wEMG/nForce ratio approximately 26% higher than males across all tasks. The wEMG/nForce ratio was always higher when pulling at 150 cm compared to pulling at 100 cm, but handle height did not appear to influence wEMG/nForce when pushing. Conclusions: Females appear to be at a higher risk for muscular overload in the pushing and pulling tasks examined here. Adjusting the height of handles according to the task conditions can be a useful intervention to lower muscular demands.

Selective Stimulation of Facial Muscles Following Chronic Intraneural Electrode Array Implantation and Facial Nerve Injury in the Feline Model.

Our group has previously shown that activation of specific facial nerve (FN) fiber populations and selective activation of facial musculature can be achieved through acute intraneural multichannel microelectrode array (MEA) implantation in the feline model. Selective stimulation of facial muscles will be maintained in the setting of 1) chronic and 2) acute MEA implantation after FN injury and subsequent recovery. This study included seven cats. In three cats with normal facial function, 4-channel penetrating MEAs were implanted chronically in the FN and tested biweekly for 6 months. Electrical current pulses were delivered to each channel individually, and elicited electromyographic (EMG) voltage outputs were recorded for each of several facial muscles. For FN injury experiments, two cats received a standardized hemostat-crush injury, and two cats received a transection-reapproximation injury to the FN main trunk. These four underwent acute implantation of MEA and EMG recording in terminal experiments 4 months postinjury. Stimulation through individual channels selectively activated restricted nerve populations, resulting in activation of individual muscles in cats with chronic MEA implantation and after nerve injury. Increasing stimulation current levels resulted in increasing EMG voltage responses in all patients. Nerve histology showed only minor neural tissue reaction to the implant. We have established in the animal model the ability of a chronically implanted MEA to selectively stimulate restricted FN fiber populations and elicit activations in specific facial muscles. Likewise, after FN injury, selective stimulation of restricted FN fiber populations and subsequent activation of discrete facial muscles can be achieved after acute MEA implantation.

The effects of noradrenergic and antimuscarinic agents on upper airway dilator muscle activity, breathing and sleep in healthy individuals

The effects of noradrenergic and antimuscarinic agents on upper airway dilator muscle activity, breathing and sleep in healthy individuals

Associations between lower-limb muscle activation and knee flexion in post-stroke individuals: A study on the stance-to-swing phases of gait.

Reduced knee flexion is a leading feature of post-stroke gait, but the causes have not been well understood. The purpose of this study was to investigate the relationship between the knee flexion and the lower-limb muscle activation within the stance-to-swing phases of gait cycle in the post-stroke hemiplegic patients. Ten stroke patients and 10 age- and gender-matched healthy subjects participated in the experiment. The lower-limb kinematic signals and the surface electromyography (sEMG) signals of the left and right rectus femoris (RF), biceps femoris (BF) and lateral gastrocnemius (GS) were recorded during walking. The angle range (AR) of knee flexion, the root mean square (RMS) and the mean frequency (MNF) of sEMG signals were calculated from the terminal stance (TSt) to the initial swing (ISw) phases of gait cycle. Stroke patients showed lower bilateral AR of knee flexion and lower RMS of GS on the paretic side, but higher MNF of RF on the non-paretic side compared with the controls. Within the stroke patients, significant differences were found between their paretic and non-paretic limbs in the AR of knee flexion, as well as in the RMS and MNF of GS (p < 0.05). Regression analysis showed that the RMS of BF, MNF of BF and MNF of GS explained 82.1% of variations in AR of knee flexion on paretic side (r2 = 0.821). But the RMS and MNF of all the muscles (including the RF, GS and BF) could explain 65.6% of AR of knee flexion variations on the non-paretic side (r2 = 0.656), and 45.2% of variations for the healthy subjects (r2 = 0.452). The reduced knee flexion during gait was associated with altered magnitude and frequency of muscle contractions and with simplified muscle synergy in the post-stroke hemiplegic patients. Identifying the muscles that are responsible for knee stiffness may facilitate improvement of rehabilitation strategy for post-stroke gait.

Skeletal muscle mitochondrial mass is linked to lipid and metabolic profile in individuals with spinal cord injury.

Changes in metabolism and body composition after spinal cord injury (SCI) predispose individuals to obesity, type II diabetes, and cardiovascular disease. A link between lean mass and skeletal muscle mitochondrial mass has been reported but it is unknown how skeletal muscle mitochondrial mass and activity impact metabolic health. This study examined the relationship between skeletal muscle mitochondrial mass, activity and metabolic profile in individuals with chronic SCI. Twenty-two men with motor complete SCI participated in the study. Citrate synthase (CS) and complex III (CIII) activity was measured in vastus lateralis biopsies. Metabolic profile was assessed by intravenous glucose tolerance test, basal metabolic rate (BMR), maximum oxygen uptake (VO2 peak) and blood lipid profile. Skeletal muscle CS activity was negatively related to the cholesterol:high density lipoprotein cholesterol (HDL-C) ratio and triglycerides (r=-0.60, p=0.009; r=-0.64, p=0.004, respectively). CS activity was positively related to insulin sensitivity and BMR (r=0.67, p=0.006; r=0.64, p=0.005, respectively). Similar relationships were found for CIII and metabolic profile, but not CIII normalized to CS. Many of the relationships between CS and metabolism remained significant when age, level of injury, or time since injury were accounted for. They also remained significant when CS activity was normalized to total lean mass. These results suggest that an increase in skeletal muscle mitochondrial mass is associated with improved metabolic health independent of age, level of injury, or time since injury in individuals with chronic SCI. This highlights the importance of maintaining and improving mitochondrial health in individuals with SCI.

Lower-Extremity Muscle Activity, Kinematics, and Dynamic Postural Control in Individuals With Patellofemoral Pain

Altered lower-extremity muscle activity has been associated with lower-extremity kinematics in individuals with patellofemoral pain (PFP). However, few studies have examined these relationships, and the results are inconsistent. To compare the lower-extremity muscle activity, kinematics, pain level, and reach distance during the anterior reach of the star excursion balance test (SEBT) between participants with PFP and healthy individuals (control [CON] group). Case control. Research laboratory. Twenty-eight (PFP = 14 and CON = 14) participants volunteered. Each participant performed 3 maximal voluntary isometric contractions of the gluteus maximus, gluteus medius (GMED), adductor longus (AL), and vastus medialis, and 5 anterior reaches of the SEBT. Three-dimensional joint kinematics of the hip and knee at the time of touchdown of the SEBT and integrated electromyography of each muscle were recorded during the descent phase of the SEBT. Coactivation ratios between the GMED and AL were calculated (GMED/AL). Pain level was assessed at the baseline and during performance of the SEBT, using a visual analog scale. Participants with PFP demonstrated decreased GMED/AL coactivation ratio (P = .01) and shorter reach distance (P = .01) during anterior reach of the SEBT compared with the CON group. Participants with PFP demonstrated higher pain levels at baseline (P = .03) and during test performance (P < .001) compared with the CON group and increased pain level during the test performance compared with the baseline (P < .001). No other significant differences were observed. There were alterations in muscle activity during SEBT performance, suggesting that overactivity of AL relative to GMED is a unique neural recruitment pattern in those with PFP. However, hip and knee joint kinematics did not seem to contribute to deficits in the anterior reach distance, suggesting a need for continued assessment of these deficiencies.

How does the PowersTM strap influence lower limb muscle activation in individuals with patellofemoral pain?

How does the PowersTM strap influence lower limb muscle activation in individuals with patellofemoral pain?