Relative Muscle Activity Research Articles

Relevance of adding a triangular dynamic cushion on a traditional chair: A 3D-analysis of seated schoolchildren

BackgroundLow back pain is highly prevalent in the general population and is even reported as early as at primary school. A poor sitting position has been suggested as an etiologic factor. This study analysed, in primary schoolchildren, the influence of a triangular dynamic cushion that aims to help children maintain their physiological lumbar lordosis and to induce movement to reduce the static effect of the sitting position. MethodsThirty 8-year-old children took part in this study. A 3D analysis combined with electromyography was used to evaluate the biomechanics and the related muscle activation in two sitting positions (with and without a triangular cushion on a horizontal stool) during a 15-minute working task. In addition, the force of the feet on the ground was assessed with a force plate. FindingsThe cushion improved the trunk–thighs angle, lumbar lordosis, anterior pelvis tilt, and feet support on the ground (p<0.0001). In addition, sitting on the cushion appeared to be more dynamic (p<0.05) and induced a decrease of the lumbar paravertebral muscle activity (p<0.01). InterpretationSitting on a dynamic triangular cushion tends to favour the “ideal” siting position usually described in the literature and to decrease the level of paravertebral muscle recruitment. Seeing that sitting position is a risk factor to develop low back pain, the cushion could be a solution to prevent it.

Compensatory effects following unilateral diaphragm paralysis

Injury to nerves innervating respiratory muscles such as the diaphragm muscle results in significant respiratory compromise. Electromyography (EMG) and transdiaphragmatic pressure (Pdi) measurements reflect diaphragm activation and force generation. Immediately after unilateral diaphragm denervation (DNV), ventilatory behaviors can be accomplished without impairment, but Pdi generated during higher force non-ventilatory behaviors is significantly decreased. We hypothesized that 1) the initial reduction in Pdi during higher force behaviors after DNV is ameliorated after 14 days, and 2) changes in Pdi over time after DNV are associated with concordant changes in contralateral diaphragm EMG activity and ventilatory parameters. In adult male rats, the reduced Pdi during occlusion (∼40% immediately after DNV) was ameliorated to ∼20% reduction after 14 days. Contralateral diaphragm EMG activity did not significantly change immediately or 14days after DNV compared to the pre-injury baseline for any motor behavior. Taken together, these results suggest that over time after DNV compensatory changes in inspiratory related muscle activation may partially restore the ability to generate Pdi during higher force behaviors.

Correctional abilities of regular muscle activity in relation to erythrocytes’ microrheological features of rats with experimentally developed hypertension

Correctional abilities of regular muscle activity in relation to erythrocytes’ microrheological features of rats with experimentally developed hypertension

Reliability of pelvic floor muscle electromyography tested on healthy women and women with pelvic floor muscle dysfunction

ObjectivesElectromyography (EMG) is a well-established method to quantify the relative pelvic floor muscle (PFM) activity. PFM EMG has shown good reliability in healthy women. However, its reliability has not been tested in women with PFM dysfunction. The reliability of EMG analysis methods concerning EMG normalization needs to be determined to assess specific therapeutic interventions. Therefore, the aim of this study was to investigate the intra-session reliability of PFM EMG variables by using 3 different analysis methods in women with PFM dysfunction. MethodsEMG data analysis involved women who were healthy, had weak PFM and had stress urinary incontinence (SUI). We evaluated the reliability of EMG during rest and maximum voluntary contraction and compared muscle activity onset by visual determination and by calculation. All variables were checked for normality (Shapiro-Wilk). Descriptive statistics (mean, SD), systematic error within repeated measures (Wilcoxon) and reliability indexes were tested and presented descriptively (intraclass correlation coefficient [ICC], standard error of measurement [SEM], SEM%, minimal difference [MD], MD%). ResultsFor 20 women who were healthy, 17 with weak PFM and 50 with SUI, ICC values were high for all variables (0.780–0.994), and SEM and MD values were relatively high (SEM%: 7.5–15.7; MD%: 21.0–43.8). ConclusionWe need reliable methods to analyse clinical intervention studies. PFM EMG variables had high ICCs, but relatively high SEM and MD values modified the reliability. All EMG analysis methods were comparable in healthy women, but only the visual-onset determination was dependable in women with PFM dysfunction.

Consistency of surface electromyography assessment at lower limb selected muscles during vertical countermovement.

Given the difficulty of invasive methods to assess muscle action during natural human movement, surface electromyography (sEMG) has been increasingly used to capture muscle activity in relation to kinesiological analysis of specific tasks. Isolated isometric, concentric and eccentric forms of muscle action have been receiving the most attention for research purposes. Nevertheless natural muscle action frequently involves the use of a preceding eccentric muscle action as a form of potentiation of immediate muscle concentric action, in what is designated as muscle stretch-shortening cycle (SSC). The most frequently applied protocols for the evaluation of SSC on vertical jumps are by virtue of their reproducibility and control of experimental conditions, squat jump (SJ) without countermovement (CM), countermovement jump (CMJ) with long CM and drop jump (DJ) with short CM. The methods used to extract information and relationship of the captured signals also present a high diversity, with the question about the consistency of the methods and obtained results. The objective of this study is to evaluate the consistency of the analysis and results by applying different EMGs signal analysis techniques related to strategic muscle groups of the lower limbs at different countermovement evaluated in vertical jumps. Raw sEMG signals of 5 lower limb muscles of 6 subjects during SJ, CMJ and DJ were rectified, filtered and obtained their envelope, and then correlated (CR) for detection of synergistic, agonist and antagonist activity, applied principal component analysis (PCA) for the detection of uncorrelated components explaining maximum variability and normalized cross-correlation (CCRN) for detection of maximum correlations and time lag. CR of EMG envelopes presented higher coactivities (CoA) in DJ relative to SJ and these CoA superior to CMJ with greater synergy in DJ relative to SJ and CMJ that present several loop cycles corresponding to time lag of activity. CCRN of the EMG envelopes presented also higher CoA in DJ when compared to SJ and both higher CoA to CMJ. PCA allowed to detect a principal component (PC) explaining 92.2% of the variability of EMG in DJ, 90.6% in SJ and 78.7% in CMJ, the second PC responsible for the explanation of 4.9% variability in DJ, 6.7% in SJ and 15.3% in CMJ.

Preference and consequences: A preliminary look at whether preference impacts oral processing in non-human primates

Non-human primates demonstrate food preferences much like humans. We have little insight, however, into how those preferences impact oral processing in primates. To begin describing this relationship, we conducted a preliminary analysis measuring food preference in two tufted capuchins (Cebus apella) and comparing ranked preference to physiological variables during chewing of these foods. Food preference was assessed for each monkey across 12 foods, including monkey biscuits and 11 foods consumed by humans (e.g., various fruits and nuts). Animals chose from randomized pairs of foods to generate a ranked scale across the 12 foods. Contemporaneous with preference testing, electromyographic (EMG) activity was measured for the jaw-closing muscles to assess oral physiology during chewing of these foods. As expected, these capuchins exhibited clear preferences among these 12 foods. Based on their preferences, we identified sets of preferred and non-preferred brittle (i.e., almond versus monkey chow) and ductile (i.e., dates and prunes versus apricots) foods for physiological comparisons that broadly control variation in food mechanical properties (FMPs). As expected, oral physiology varied with FMPs in each animal. Within brittle and ductile groupings, we observed several significant differences in chewing cycle length and relative muscle activation levels that are likely related to food preference. These differences tended to be complex and individual specific. The two capuchins chewed non-preferred apricots significantly faster than preferred dates and prunes. Effect sizes for preference were smaller than those for FMPs, supporting the previous focus on FMPs in primate dietary research. Although preliminary, these results suggest that food preference may influence oral physiology in non-human primates. The prospect that this relationship exists in monkeys raises the possibility that a link between food preference and oral processing in humans may be based on shared tendencies with non-human primates, such as aversion to bitter items or preference for sweet foods.

Relative scapular muscle activity ratios are altered in subacromial pain syndrome

Coordinated muscle activity is needed for synchronized joint motion and stability. Characterizing relative scapular muscle activity deficits in participants with shoulder pain will provide foundational knowledge to develop rehabilitation programs. Participants were recruited with subacromial pain syndrome and an asymptomatic control group matched for age, gender, and dominant arm (N = 56). Surface electromyographic muscle activity was recorded from the upper, middle, and lower trapezius (UT, MT, LT) and serratus anterior (SA) during 5 repetitions of a weighted arm elevation task. Muscle activity was normalized to a reference contraction and then expressed as UT/MT, UT/LT, UT/SA, and LT/SA ratios. Ratios were compared between groups and across 3 arm angle intervals during ascending and descending elevation. A 2 × 3 mixed-model analysis of variance yielded a group main effect for the UT/LT ratio, with a higher ratio in the subacromial pain group during ascending (mean difference, 0.92; P = .008) and descending (mean difference, 0.70; P = .030). For the LT/SA ratio, there was a group effect: a lower ratio in the subacromial group during ascending (mean difference, -0.25; P = .026) and descending (mean difference, -0.51; P = .032). There were no differences for the UT/MT or UT/SA. There is a disruption in coordination between the LT and SA and the UT and LT during an arm elevation task in patients with subacromial pain syndrome. The LT was part of both altered ratios, indicating the relative importance of the LT. Future research should determine if exercises aimed at restoring the dysfunctional LT/SA and UT/LT force couples are beneficial to reduce shoulder pain and disability in patients with unilateral shoulder pain.

Leg and trunk muscle coordination and postural sway during increasingly difficult standing balance tasks in young and older adults

Ageing impairs body balance and increases older adults’ fall risk. Balance training can improve intrinsic fall risk factors. However, age comparisons of muscle activity responses during balance tasks are lacking. This study investigated relative muscle activity, muscle coordination and postural sway during various recommended static balance training tasks.Muscle activity (%MVC), amplitude ratios (AR) and co-activity (CAI) were determined during standing tasks for 30s (1: double limb stance on a foam surface, eyes open; 2: double limb stance on firm ground, eyes closed; 3: double limb stance, feet in step position on a foam surface, eyes open; 4: double limb stance, feet in step position on firm ground, eyes closed; 5: single limb stance on firm ground, eyes open) in 20 healthy young adults (24±2 y) and 20 older adults (73±6 y). Surface electromyography (SEMG) was applied (SENIAM guidelines) to ankle (tibialis anterior, soleus, medial gastrocnemius, peroneus longus) and thigh (vastus lateralis, vastus medialis, biceps femoris, semitendinosus) muscles (non-dominant leg). Electrodes over trunk (multifidus and internal oblique) muscles were applied bilaterally.Two- to six-fold higher levels of relative muscle activity were found in older adults for ankle (0.0002<p<0.001), thigh (0.0008<p<0.075) and trunk (0.001<p<0.036) muscles. Co-activation was elevated in young adults for the trunk (0.001<p<0.031) and in older adults for the ankle (0.009<p<0.03). Age-group differences were observed for muscle coordination patterns during all stance conditions at the ankle (0.06<ηp2<0.28) and the trunk (0.14<ηp2<0.23).Older adults had higher electrophysiological costs for all stance conditions. Muscle coordination showed inverse activity patterns at the ankle and trunk. Optimal balance and strength training programs should take into account age-specific alterations in muscle activity.

Fatiguing a Single Limb leads to Bilateral Changes in Postural Tremor and Forearm Muscle Activity

For healthy adults, the physiological tremor within a single limb segment is uncorrelated to that in the contralateral limb. However, it has been suggested that some bilateral relation for tremor does exist, but that this would only emerge under conditions where the neuromuscular system is perturbed such as during unilateral fatigue. PURPOSE: To assess the effect of externally loading the index finger on bilateral tremor dynamics and forearm muscle activity. METHODS: Eighteen young adults participated in the study (mean age 22.4+4.2 yrs.). For all tasks, bilateral hand and finger tremor and forearm surface EMG activity (extensor digitorum) were collected. Subjects were seated with both forearms resting on a flat surface and their hands and index fingers extended (unsupported). Three 30 s trials were collected under this condition. For the fatigue conditions, a 400 gram weight was suspended from the index finger of one limb. Subjects were required to hold both fingers in an extended (horizontal) position with the weight attached for two, 2-min trials (rests were given between trials). The fatigue protocol was then repeated for the opposite limb. RESULTS: As expected, fatiguing a single limb led to significant increases in tremor amplitude (pre-fatigue: 0.18+0.04 ms-2; post: 0.37+0.08 ms-2, p<0.02), extensor muscle activity (pre: 0.11+0.04 mV; Post: 0.24+0.06 mV, p<0.05). In addition, fatiguing a single limb led to changes in the contralateral (un-weighted) limb, significant increases in the amount of muscle activity (pre: 0.10+0.03 mV; Post: 0.17+0.03 mV, p<0.05) and the amplitude of finger tremor (pre: 0.16+0.05 ms-2; post: 0.27+0.04 ms-2, p<0.05). However, these contralateral effects were observed even though there was no evidence of inter-limb coupling of tremor (r’s=0.08-0.18, p=0.64). CONCLUSION: Overall, the results demonstrated that the effects of fatiguing a single, distal limb segment are not restricted to that effector unit. Loading the index finger of one limb led to bilateral increases in both tremor amplitude and related forearm muscle activity. However, these changes were present even though there was no evidence of any tremor coupling between limbs. The findings illustrate that these bilateral effects may be mediated by an overflow effect caused by increased neural drive to the exercising limb.

Dynamic Frequency Analyses of Lower Extremity Muscles during Sit-To-Stand Motion for the Patients with Knee Osteoarthritis

ObjectiveMuscle activities during the sit-to-stand motion (STS) are characterized by coordinated movements between hip extensors and knee extensors. However, previous reports regarding the STS and lower extremity muscle activities have focused on some quantitative assessment, but little qualitative research. This study aimed to examine the muscle activities of the lower extremity both quantitatively and qualitatively.MethodsStudy participants included 13 patients with knee osteoarthritis (knee OA) and 11 age-matched asymptomatic controls. The task was STS from a chair with a height-adjustable seat. EMG activities were acquired using surface electromyogram. The root mean square signals normalized as a percentage of maximum voluntary isometric contraction values (RMS%MVC) and the mean power frequency (MPF) were calculated.ResultsDuring STS, knee OA patients had increased RMS%MVC of the vastus medialis and raised MPF of the rectus femoris before buttocks-off.ConclusionThese findings suggest that STS of knee OA patients not only increased relative muscle activity of the vastus medialis, but also enlisted the rectus femoris in knee extension to improve muscle contraction force by activating more type II fibers to accomplish buttocks-off.

Relative activity of respiratory muscles during prescribed inspiratory muscle training in healthy people.

[Purpose] This study aimed to determine the effects of different intensities of inspiratory muscle training on the relative respiratory muscle activity in healthy adults. [Subjects and Methods] Thirteen healthy male volunteers were instructed to perform inspiratory muscle training (0%, 40%, 60%, and 80% maximal inspiratory pressure) on the basis of their individual intensities. The inspiratory muscle training was performed in random order of intensities. Surface electromyography data were collected from the right-side diaphragm, external intercostal, and sternocleidomastoid, and pulmonary functions (forced expiratory volume in 1 s, forced vital capacity, and their ratio; peak expiratory flow; and maximal inspiratory pressure) were measured. [Results] Comparison of the relative activity of the diaphragm showed significant differences between the 60% and 80% maximal inspiratory pressure intensities and baseline during inspiratory muscle training. Furthermore, significant differences were found in sternocleidomastoid relative activity between the 60% and 80% maximal inspiratory pressure intensities and baseline during inspiratory muscle training. [Conclusion] During inspiratory muscle training in the clinic, the patients were assisted (verbally or through feedback) by therapists to avoid overactivation of their accessory muscles (sternocleidomastoid). This study recommends that inspiratory muscle training be performed at an accurate and appropriate intensity through the practice of proper deep breathing.

Relative index of ankle muscle activations on agonistic phase between subjects with and without flat foot

Background: Although co-activation of ankle muscles has been reported, relative ankle muscle activation in subjects with flat foot has not been carefully investigated. The aim of this study was to compare the relative activation index (RAI) on the tibialis anterior (TA) and medial gastrocnemius (GTN) muscles during active ankle range of motion (ROM) between subjects with and without flat foot. Methods: There were 17 subjects with flat foot and 17 age- and gender-matched control subjects who participated in this study. The RAI based on electromyography (EMG) was measured during the agonist phase at a controlled velocity of ankle motion (10°/second). The subject was seated upright with the tested foot held firmly onto a footplate that was attached to a torque sensor. The ankle being measured was strapped to the leg support of the Intel stretch device at 60° of knee flexion. The RAI was analyzed by the summation of EMG activity from the agonistic time window divided by the total EMG activity during full active ankle ROM. Results: The RAI was significantly different on the TA muscle (t = 3.08, P = 0.004), but no difference was found on the GTN muscle (t = -1.24, P = 0.23) in subjects with flat foot. There was an interaction between group and RAI (F =7.89, P = 0.007); however, the RAI demonstrated no interaction with age (F = 2.59, P = 0.14), height (F = 3.73, P = 0.06), or weight (F = 2.96, P = 0.09). Conclusions: The RAI indicated a lack of TA muscle activation in the flat foot group. Such dissociated activation in the flat foot group might be relevant to the inefficiency of synergistic motions. The relative activation of the agonistic phase needs to be further investigated to compare co-activation of synergistic muscle activation with various functional tasks.

Perception of Muscular Effort During Dynamic Elbow Extension in Multiple Sclerosis

ObjectiveTo investigate the perception of muscular effort in individuals with multiple sclerosis (MS) and healthy controls during dynamic contractions. DesignCase-control study. SettingMS day care center. ParticipantsIndividuals with MS (n=28) and controls (n=28) (N=56). InterventionsNot applicable. Main Outcome MeasuresPerceived muscular effort during dynamic elbow extensions was rated at 9 different weight intensities (10%–90% of 1-repetition maximum) in a single-blind, randomized order using the OMNI-Resistance Exercise Scale. Muscle activity of the triceps brachii muscle (lateral head) was measured via surface electromyography and normalized to maximal voluntary excitation. ResultsAccording to OMNI-level ratings, significant main effects were found for the diagnostic condition (F=27.33, P<.001, η2=.11), indicating 0.7 (95% confidence interval [CI], 0.3–1.1) lower mean OMNI-level ratings for MS, and for the intensity level (F=46.81, P<.001, η2=.46), showing increased OMNI-level ratings for increased intensity levels for both groups. Furthermore, significant main effects were found for the diagnostic condition (F=16.52, P<.001, η2=.07), indicating 7.1% (95% CI, −8.6 to 22.8) higher maximal voluntary excitation values for MS, and for the intensity level (F=33.09, P<.001, η2=.36), showing higher relative muscle activities for increasing intensity levels in both groups. ConclusionsSimilar to controls, individuals with MS were able to differentiate between different intensities of weight during dynamic elbow extensions when provided in a single-blind, randomized order. Therefore, perceived muscular effort might be considered to control resistance training intensities in individuals with MS. However, training intensity for individuals with MS should be chosen at approximately 1 OMNI level lower than recommended, at least for dynamic elbow extension exercises.

Alterations of relative muscle contribution induced by hemiplegia: Straight and turning gaits

Little information is available about the characteristics in the turning gait of hemiplegic elderly, which occurs frequently in daily life. It is also difficult to examine the altered characteristics due purely to hemiplegia because of no consideration of aging-related factors. The aim of this study was to identify the altered characteristics of relative muscle activation in both straight and turning gaits together due to hemiplegia, through comparing healthy and hemiplegic elderly. Six healthy elderly and six hemiplegic elderly were participated. The center of body mass (COM) and the lower extremity joint angles were measured during straight and turning gaits at self-selected speed, using a motion capture system. A surface wireless electromyogram (EMG) system was used together to identify muscle contributions. Mediolateral (ML) sways of upper-body in hemiplegic elderly were ~174% for straight gait and ~26% for turning gait. Lower extremity joint angles in hemiplegic elderly were generally reduced by ~60-70% for both gaits. Muscle co-activation and relative muscle contributions were generally altered at all phases in hemiplegic elderly, but the patterns were different between straight and turning gaits. This study confirmed that the ML sways of hemiplegic elderly moved towards the non-paretic side more and joint angles showed large decreases. Muscles acted with different contributions, depending on the gait.

Ankle muscle strength influence on muscle activation during dynamic and static ankle training modalities

Muscle weakness is considered a risk factor for ankle injury. Balance training and barefoot running have been used in an attempt to strengthen the muscles crossing the ankle. It is expected that training tasks that successfully strengthen the ankle would elicit increased muscular activity. However, it is unknown how an individual's ankle strength will influence the muscle activity used during a given task. Twenty-six participants performed dynamic (shod, barefoot running) and static tasks (squat on ground, squat on ®Bosu Ball) believed to strengthen the muscles surrounding the ankle. Electromyographic signals of the tibialis anterior, peroneus longus, gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) were recorded and analysed using a non-linearly scaled wavelet analysis. Participants were divided into a strong group and a weak group according to their isometric plantar-flexion torque. The weak group required more relative GL and GM muscle activity during each training task compared to the strong group. No difference was observed between shod and barefoot running. There was a significant effect of training task on muscle activation level for the weak group. Differences in ankle strength had a significant impact on muscle activation.

Bracing of the trunk and neck has a differential effect on head control during gait.

During gait, the trunk and neck are believed to play an important role in dissipating the transmission of forces from the ground to the head. This attenuation process is important to ensure head control is maintained. The aim of the present study was to assess the impact of externally restricting the motion of the trunk and/or neck segments on acceleration patterns of the upper body and head and related trunk muscle activity. Twelve healthy adults performed three walking trials on a flat, straight 65-m walkway, under four different bracing conditions: 1) control-no brace; 2) neck-braced; 3) trunk-braced; and 4) neck-trunk braced. Three-dimensional acceleration from the head, neck (C7) and lower trunk (L3) were collected, as was muscle activity from trunk. Results revealed that, when the neck and/or trunk were singularly braced, an overall decrease in the ability of the trunk to attenuate gait-related oscillations was observed, which led to increases in the amplitude of vertical acceleration for all segments. However, when the trunk and neck were braced together, acceleration amplitude across all segments decreased in line with increased attenuation from the neck to the head. Bracing was also reflected by increased activity in erector spinae, decreased abdominal muscle activity and lower trunk muscle coactivation. Overall, it would appear that the neuromuscular system of young, healthy individuals was able to maintain a consistent pattern of head acceleration, irrespective of the level of bracing, and that priority was placed over the control of vertical head accelerations during these gait tasks.

Resisted Side Stepping: The Effect of Posture on Hip Abductor Muscle Activation.

Controlled laboratory study, repeated-measures design. To compare hip abductor muscle activity and hip and knee joint kinematics in the moving limb to the stance limb during resisted side stepping, and to determine whether muscle activity was affected by the posture (upright standing versus squat) used to perform the exercise. Hip abductor weakness has been associated with a variety of lower extremity injuries. Resisted side stepping is often used as an exercise to increase strength and endurance of the hip abductors. Exercise prescription would benefit from knowing the relative muscle activity level generated in each limb and for different postures during the side-stepping exercise. Twenty-four healthy adults participated in this study. Kinematics and surface electromyographic data from the gluteus maximus, gluteus medius, and tensor fascia lata were collected as participants performed side stepping with a resistive band around the ankle, while maintaining each of 2 postures: (1) upright standing and (2) squat. Mean normalized electromyographic signal amplitude of the gluteus maximus, gluteus medius, and tensor fascia lata was higher in the stance limb than in the moving limb (P≤.001). Gluteal muscle activity was higher, whereas tensor fascia lata muscle activity was lower, in the squat posture compared to the upright standing posture (P<.001). Hip abduction excursion was greater in the stance limb than in the moving limb (P<.001). The 3 hip abductor muscles respond differently to the posture variations of the side-stepping exercise in healthy individuals. When prescribing resisted side-stepping exercises, therapists should consider the differences in hip abductor activation across limbs and variations in trunk posture.

Linear summation of outputs in a balanced network model of motor cortex.

Given the non-linearities of the neural circuitry's elements, we would expect cortical circuits to respond non-linearly when activated. Surprisingly, when two points in the motor cortex are activated simultaneously, the EMG responses are the linear sum of the responses evoked by each of the points activated separately. Additionally, the corticospinal transfer function is close to linear, implying that the synaptic interactions in motor cortex must be effectively linear. To account for this, here we develop a model of motor cortex composed of multiple interconnected points, each comprised of reciprocally connected excitatory and inhibitory neurons. We show how non-linearities in neuronal transfer functions are eschewed by strong synaptic interactions within each point. Consequently, the simultaneous activation of multiple points results in a linear summation of their respective outputs. We also consider the effects of reduction of inhibition at a cortical point when one or more surrounding points are active. The network response in this condition is linear over an approximately two- to three-fold decrease of inhibitory feedback strength. This result supports the idea that focal disinhibition allows linear coupling of motor cortical points to generate movement related muscle activation patterns; albeit with a limitation on gain control. The model also explains why neural activity does not spread as far out as the axonal connectivity allows, whilst also explaining why distant cortical points can be, nonetheless, functionally coupled by focal disinhibition. Finally, we discuss the advantages that linear interactions at the cortical level afford to motor command synthesis.

Muscle activity of leg muscles during unipedal stance on therapy devices with different stability properties

ObjectivesTo test the hypotheses that less stable therapy devices require greater muscle activity and that lower leg muscles will have greater increases in muscle activity with less stable therapy devices than upper leg muscles. DesignCross-sectional laboratory study. SettingLaboratory setting. ParticipantsTwenty-five healthy subjects. Main outcome measuresElectromyographic activity of four lower (gastrocnemius medialis, soleus, tibialis anterior, peroneus longus) and four upper leg muscles (vastus medialis and lateralis, biceps femoris, semitendinosus) during unipedal quiet barefoot stance on the dominant leg on a flat rigid surface and on five therapy devices with varying stability properties. ResultsMuscle activity during unipedal stance differed significantly between therapy devices (P < 0.001). The order from lowest to highest relative muscle activity matched the order from most to least stable therapy device. There was no significant interaction between muscle location (lower versus upper leg) and therapy device (P = 0.985). Magnitudes of additional relative muscle activity for the respective therapy devices differed substantially among lower extremity muscles. ConclusionsThe therapy devices offer a progressive increase in training intensity, and thus may be useful for incremental training programs in physiotherapeutic practice and sports training programs.

Neuromuscular strategies contributing to faster multidirectional agility performance

The aim of this study was to first determine differences in neuromuscular strategy between a faster and slower agility performance, and second compare differences in muscle activation strategy employed when performing two closely executed agility movements. Participants recruited from an elite female basketball team completed an ultrasound to determine quadriceps muscle-cross sectional area; reactive isometric mid-thigh pull to determine the rate of muscle activation, rate of force development, pre-motor time and motor time; and multidirectional agility tests completing two directional changes in response to a visual stimulus. Peak and average relative muscle activation of the rectus femoris, vastus medialis, vastus lateralis, biceps femoris, semitendinosus and gastrocnemius were measured 100ms prior to heel strike (pre-heel strike) and across stance phase for both directional changes. Faster agility performance was characterized by greater pre-heel strike muscle activity and greater anterior muscle activation during stance phase resulting in greater hip and knee extension increasing propulsive impulse. Differences between directional changes appear to result from processing speed, where a greater delay in refractory times during the second directional change resulted in greater anterior muscle activation, decelerating the body while movement direction was determined.