What triggers the continuous muscle activity during upright standing?

Functional electrical stimulation (FES) pedaling with the muscles of the upper leg has been shown to provide benefit to spinal cord injured (SCI) individuals. FES pedaling with electrical stimulation timing patterns that minimize the stress-time integral of activated muscles has been shown to increase the work individuals can perform during the exercise compared to existing FES stimulation timing patterns. Activation of the lower leg muscles could further enhance the benefit of FES pedaling by increasing the metabolic response to the exercise. For SCI individuals, the objectives of this study were to experimentally determine whether FES pedaling with the upper and lower leg muscles would affect the work generated and increase the physiological responses compared to pedaling with the upper leg muscles alone. Work, rate of oxygen consumption ·VO₂, and blood lactate data were measured from nine SCI subjects (injury level T4-T12) as they pedaled using upper leg and upper and lower leg muscle groups on repeated trials. The subjects performed 6% more work with the upper and lower legs than with the upper legs alone, but the difference was not significant (p = 0.2433). The average rate of oxygen consumption associated with the upper leg muscles (441 ±231 mL/min) was not significantly different from the corresponding average for the upper and lower legs (473 ±213 mL/min) (p = 0.1176). The blood lactate concentration associated with the upper leg muscles (5.9 ±2.3 mmoles/L) was significantly lower than the corresponding average for the upper and lower legs (6.8 ±2.3 mmoles/L) (p = 0.0049). The results indicate that electrical stimulation timing patterns that incorporate the lower leg muscles do increase the blood lactate concentrations. However, there was not enough evidence to reject the null hypothesis that stimulating the lower leg muscles affected the work accomplished or increased the rate of oxygen consumption. In conclusion, incorporating the lower leg muscles in the exercise does not lead to negative effects and could result in enhanced exercise outcomes in the long term.

This study was designed to provide evidence for the hypothesis that human balance corrections in response to pitch perturbations are controlled by muscle action mainly about the ankle and knee joints, whereas balance corrections for roll perturbations are controlled predominantly by motion about the hip and lumbro-sacral joints. A dual-axis rotating support surface delivered unexpected random perturbations to the stance of 19 healthy young adults through eight different directions in the pitch and the roll planes and three delays between pitch and roll directions. Roll delays with respect to pitch were no delay, a short 50-ms delay of roll with respect to pitch movements, (chosen to correspond to the onset time of leg muscle stretch reflexes), and a long 150-ms delay between roll and pitch movements (chosen to shift the time when trunk roll velocity peaks to the time when trunk peak pitch velocity normally occurs). Delays of stimulus roll with respect to pitch resulted in delayed roll responses of the legs, trunk, arms, and head consistent with stimulus delay without any changes in roll velocity amplitude. Delayed roll perturbations induced only small changes in the pitch motion of the legs and trunk; however, major changes were seen in the time when roll motion of the trunk was arrested. Amplitudes and directional sensitivity of short-latency (SL) stretch reflexes in ankle muscles were not altered with increasing roll delay. Small changes to balance correcting responses in ankle muscles were observed. SL stretch reflexes in hip and trunk muscles were delayed, and balance-correcting responses in trunk muscles became split into two distinct responses with delayed roll. The first of these responses was small and had a directional responsiveness aligned more along the pitch plane. The main, larger, response occurred with an onset and time-to-peak consistent with the delay in trunk roll displacement and its directional responsiveness was roll oriented. The sum of the amplitudes of these two types of balance-correcting responses remained constant with roll delay. These results support the hypothesis that corrections of the body's pitch and roll motion are programmed separately by neural command signals and provide insights into possible triggering mechanisms. The evidence that lower leg muscle balance-correcting activity is hardly changed by delayed trunk roll also indicates that lower leg muscle activity is not predominant in correcting roll motion of the body. Lower leg and trunk muscle activity appears to have a dual action in balance corrections. In trunk muscles the main action is to correct for roll perturbations and the lesser action may be an anticipatory stabilizing reaction for pitch perturbations. Likewise, the small changes in lower leg muscle activity may result from a generalized stabilizing reaction to roll perturbations, but the main action is to correct for pitch perturbations.

Background Self-report instruments classify ankle instability (AI) by self-perceived symptoms and movement deficits however, movement neuromechanics in this patient population are quite variable. For this reason it is difficult to identify specific neuromechanical alterations that might lead to poor movement strategies and perpetuate AI. Objective To identify multiple clusters of lower extremity neuromechanics, representing movement patterns in patients with AI. Design Descriptive laboratory study. Setting Research laboratory. Patients 100 subjects (22 ± 2 yrs) with a history of ankle sprains (4.4 ± 3.2), scored below 90% (83 ± 9) on the FAAM ADL, below 75% (62 ± 13) on the FAAM Sport, reported at least 2 “yes” responses (4 ± 1) on the MAII, and had no sprain in the previous 3 months. Interventions High-speed video (250 Hz) and force plate (2500 Hz) data were used to estimate sagittal and frontal plane ankle, knee, and hip angles and joint torques during 5 trials of a max vertical jump, onto a force plate, immediately followed by a lateral jump. EMG data (2000 Hz) were collected from lower extremity muscles. Main outcome measurements A curve or “function” was generated for each trial collected during the stance phase of the jump task. Relevant DVs were grouped according to their relationship of a movement pattern. Bayesian statistical modelling was used to create clusters from the functions. Functions were clustered using the multiple landmarks that characterised the grouped function. Cross-classification matrices were used to measure cluster dependences across the grouped variables. Results Distinct clusters were identified among the grouped variables. Summary functions/curves represent each distinct cluster. The maximum proportion of subjects sharing similar clusters from at least two different grouped variable characteristics (joint and plane) ranged from 0.10 to 0.58. Conclusions Multiple distinct joint torque functions were identified in a “homogenous” group of patients with self-reported AI, suggesting that multiple distinct neuromechanical alterations exist in an AI patient population. These data should be considered when using self-report instruments to identify AI, as these instruments may not be sensitive enough to provide evidence of a single movement strategy that places AI patients at risk. More data are needed to provide clinical identification techniques for each of the data clusters.

In activities of daily living, people walk at different speeds with or without carrying additional loads. In this study, we sought to examine how human adults manage these commonly encountered additional demands during walking. We measured electromyography (EMG), triceps surae H‐reflexes, joint motion and ground reaction forces (GRF) while participants walked at 1.0 m/s and 1.5 m/s with or without an additional 20.4 kg of weight (the equivalent of 23–36% bodyweight). Faster walking was accompanied by a universal increase in burst EMG amplitude across flexors and extensors of upper and lower leg muscles (with most notable increases found in the plantarflexors) while burst patterns of activity were maintained. In addition, the range of motion increased at the ankle, knee and hip joints, while the step cycle duration was shortened. In bearing additional weight, upper and lower leg extensor activity, especially early stance quadriceps activity, was increased while joint motion was minimally affected at the ankle and knee (but not hip). When walking faster and carrying additional weight, changes in locomotor EMG (except for plantarflexors) and knee and hip joint motion displayed combined features of those two additional demands; changes in plantarflexor activity and ankle joint motion were more complex. Locomotor H‐reflexes were larger at 1.5 m/s than at 1.0 m/s only when carrying additional weight. In generating plantarflexor activity and controlling ankle joint motion for propulsive force generation when walking faster and carrying additional weight, multiple mechanisms of both spinal and supraspinal origin may be involved.

The patterns of joint torques and movement strategies underlying human balance corrections were examined using a postural model. Two types of support-surface perturbation, dorsiflexion rotation (ROT) and rearward translation (TRANS), were employed. These two perturbations were adjusted to produce similar profiles of ankle dorsiflexion in order to obtain information on the role of lower leg proprioceptive inputs on triggering balance corrections. In addition, the dependence of balance control on head angular and linear accelerations was investigated by comparing the responses of normal and vestibularly deficient subjects under eyes-closed and eyes-open conditions. Differences in ROT and TRANS movement strategies were examined in three ways First, the amplitude and polarity of active joint torques were analysed. These were obtained by altering joint torques applied to a postural model until movements of the model accurately duplicated those of measured responses. Second, the pattern of body-segment angular movements depicted by stick figures moving in response to the computed joint torques was investigated. Third, the peak amplitude and patterns of crosscorrelations between joint torques were measured. Active ankle, knee, and hip joint torques computed for normal subjects rotated the body forward for ROT. In the case of TRANS, computed active torques in normals were of opposite polarity to those of ROT and reversed the forward motion of the body. Subjects with vestibular deficits had lower amplitude torques for ROT and failed to counter the platform rotation. Hip torques for TRANS in vestibular deficient subjects were of opposite polarity to those of normal subjects and resulted in excessive forward trunk rotation. Normally, neck torques acted to stabilize the head in space when trunk angular velocity peaked. Vestibular deficient subjects displayed head movements in response to ROT similar to those generated when neck torques were absent. For TRANS, these same subjects exhibited overcompensatory neck torques. Stick figures of normal responses indicated a stiffening of the body into a leg and a trunk-head link for ROT and a flexible multilink motion for TRANS. Likewise, normal response strategies, defined by using crosscorrelations of joint torques, differed for ROT and TRANS. All joint torque crosscorrelations were significant for TRANS. Neck torques led those of all other joint torques by 40 ms or more, and hip joint led ankle torques by 30 ms. Joint torque correlations for ROT were organised around hip and ankle torques without a major correlation to neck torques. Fundamental changes in all torque crosscorrelations occurred for vestibularly deficient subjects under both eyes-open and eyes-closed conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Purpose To demonstrate the reproducibility of the diffusion properties and three-dimensional structural organization measurements of the lower leg muscles by using diffusion-tensor imaging (DTI) assessed with ultra-high-field-strength (7.0-T) magnetic resonance (MR) imaging and tractography of skeletal muscle fibers. On the basis of robust statistical mapping analyses, this study also aimed at determining the sensitivity of the measurements to sex difference and intramuscular variability. Materials and Methods All examinations were performed with ethical review board approval; written informed consent was obtained from all volunteers. Reproducibility of diffusion tensor indexes assessment including eigenvalues, mean diffusivity, and fractional anisotropy (FA) as well as muscle volume and architecture (ie, fiber length and pennation angle) were characterized in lower leg muscles (n = 8). Intramuscular variability and sex differences were characterized in young healthy men and women (n = 10 in each group). Student t test, statistical parametric mapping, correlation coefficients (Spearman rho and Pearson product-moment) and coefficient of variation (CV) were used for statistical data analysis. Results High reproducibility of measurements (mean CV ± standard deviation, 4.6% ± 3.8) was determined in diffusion properties and architectural parameters. Significant sex differences were detected in FA (4.2% in women for the entire lower leg; P = .001) and muscle volume (21.7% in men for the entire lower leg; P = .008), whereas architecture parameters were almost identical across sex. Additional differences were found independently of sex in diffusion properties and architecture along several muscles of the lower leg. Conclusion The high-spatial-resolution DTI assessed with 7.0-T MR imaging allows a reproducible assessment of structural organization of superficial and deep muscles, giving indirect information on muscle function. ©RSNA, 2018 Online supplemental material is available for this article.

The movement recovery of ankle is extremely important for patients with ankle injuries especially with the stroke hemiplegia. In this paper, a novel control method of ankle rehabilitation robot is proposed to provide continuous motion assistant. Ankle joint torque is estimated based on EMG signals to establish the relationship between joint torque and joint angle. In detail, we firstly apply a LDA algorithm for recognizing the motor patterns of ankle using two channels EMG signals collected from anterior tibial (TA) and gastrocnemius (GA). Then, the corresponding BP neural network model established in previous is selected according to identified motion pattern. The muscle activity related with identified motion pattern is used as the inputs of the BP neural network model to estimate the relevant joint torque. In order to meet the requirements of movement range for the subjects with different rehabilitation conditions, the subjects just need reset the angle range to achieve the control of continuous ankle motion with adjustable amplitude. Experimental results on nine subjects demonstrated that the ankle motion intention can be precisely predicted in advance, and the angle range of ankle motion were also adjustable based on the requirements of subjects. Key Words: sEMG, Ankle rehabilitation, Ankle joint angle.

PurposeThis study aimed to elucidate whether muscle activity (in terms of glucose uptake) between the legs can be considered symmetrical during walking. Furthermore, we aimed to determine whether the [18F]-fluorodeoxyglucose was distributed heterogeneously throughout each muscle, and if so, whether areas of high uptake would be clustered.MethodsTen healthy participants walked on a treadmill at self-selected comfortable walking speed for a total of 90 minutes, 60 minutes before and 30 minutes after intravenous injection of 50 MBq [18F]-fluorodeoxyglucose. Thereafter, a positron emission tomography/computed tomography scan of the lower limb was acquired. Three-dimensional muscle contours of 78 (= 39x2) muscles of the left and right lower limb were semi-automatically determined from magnetic resonance imaging scans. After non-rigid registration, those muscle contours were used to extract [18F]-fluorodeoxyglucose uptake from the positron emission tomography scans.ResultsLarge asymmetries were observed in the lower leg muscles (e.g. median absolute asymmetry index of 42% in the gastrocnemius medialis) and in the gluteus minimus (30% asymmetry) and gluteus medius (15% asymmetry), whereas the uptake in the thighs was relatively symmetrical between the limbs (<6% asymmetry). These were not related to limb-dominance nor to inter-limb differences in muscle volume. The [18F]-fluorodeoxyglucose distribution was not distributed normally; most voxels had a relatively low standardized uptake value, and a minority of voxels had a relatively high standardized uptake value. The voxels with higher [18F]-fluorodeoxyglucose uptake were distributed heterogeneously; they were clustered in virtually all muscles.ConclusionThe findings in this study challenge the common assumption of symmetry in muscle activity between the limbs in healthy subjects. The clustering of voxels with high uptake suggests that even in this prolonged repetitive task, different spatial regions of muscles contribute differently to walking than others.

A finite element model of an anthropomorphic test device lower limb to assess risk of injuries during vertical accelerative loading

Sensory feedback from the foot sole plays an important role in shaping human locomotion. While net muscle activity and kinematic changes have been correlated with electrical stimulation to five topographical regions of the foot, it remains unknown if these responses are similar with tactile stimulation. The purpose of this study was to use texture in foot orthosis design, applied to five distinct regions under the foot sole, and measure joint kinematics, location of center of pressure, and muscle activity of eight lower leg muscles during level and incline walking. Fifty-five healthy adults completed 48 walking trials in textured and non-textured foot orthoses. Study results confirm that tactile stimulation is stimulation-site and gait-phase specific in modulating lower leg muscle activity during walking. For example, texture under the lateral forefoot consistently generated a suppression of EMG and texture under the lateral midfoot always generated a facilitation. In early stance, adding texture under the medial midfoot or calcaneus facilitated extensor muscle activity and suppressed flexor muscle activity. Texture under the lateral midfoot or medial forefoot facilitated tibialis posterior activation. These results support the topographical organization of cutaneous mechanoreceptors in foot sole skin while considering how texture can be used in foot orthosis design to target lower leg muscular changes during locomotion.

Knowledge of muscle actions is essential for understanding biomechanics in running. In this study, 17 young runners were investigated at 13 different running speeds. Telemetric surface electromyograms from lower leg muscles were recorded continuously, and they were synchronized with the recordings of 3-dimensional ground reaction forces from a 10-m-long force platform. As expected, the rate of force production and the peak forces increased with increasing running speed. In the lateral forces, there was a short-duration inward force at the beginning of the contact followed by a longer-lasting outward force. The results revealed further the importance of preactivity and eccentric activity of the leg extensor muscles and the role of the hamstring muscles. The preactivity appears to be a preparatory requirement both for the enhancement of electromyographic activity during the braking phase and for timing of muscular action with respect to the ground contact. The increased force production with increased running speed is, furthermore, partly due to high and long-lasting activity of the hip extensor muscles during the contact phase.

Ankle sprains are one of the most common sports injuries which are about 40% of total sports injuries and 20~40% of them would be progressed to chronic ankle instability (CAI) [1]. Rehabilitation and surgical therapy have been used to treat CAI, and the open modified Brostrm operation (MBO) is the gold standard surgical procedure. There are various evaluation methods in CAI treatments, such as the interview, visual analogue scale (VAS), and the measurement of range of motion (ROM) and the ankle torque. However, in reality, it is difficult to measure the maximum ROM and torque. Therefore, some studies measured ankle ROM and torque with cadaver specimens [2,3]. In this study, both open and arthroscopic MBO were performed on cadavers, and ankle torque and angle were measured during ankle inversion using the axial-torsion testing system. Ankle stiffness was calculated from measured data, and effects of both operations were compared quantitatively. For this study, matched pairs of fresh-frozen human cadaver lower leg specimens were obtained from seven males and four females (average age 71.5 (range 58–98) years). Each specimen consisted of the distal half of a leg. The soft tissues were removed from the calcaneus and distal tibiofibular part, except for the ankle joint and ligament. The anterior talofibular ligament (ATFL) and the calcaneofibular ligament (CFL) were transected. The specimens for the arthroscopic and open MBO were chosen from the left and right legs alternately. Then, each specimen was fixed in the specially-designed jig that was mounted on the axial-torsion fatigue testing system (Instron 8874, Norwood, MA, USA). The test consisted of a single ramp from 0° to 70° by inverting the ankle at 5°/s, while measuring the angular position and resultant torque. There was no statistical difference in torque to failure between open and arthroscopic MBO. The maximum torque was 16.3±7.2 N•m at 45° for open MBO and 19.9±10.8 N•m at 40° for arthroscopic MBO (Figure ​(Figure1).1). Ankle stiffness increased faster in arthroscopic MBO (0.31±0.22 N•m/deg) than in open MBO (0.18±0.15 N•m/deg) in initial inversion range (<5°), but no statistically significant differences were observed. The maximum stiffness was 0.41±0.18 N•m/deg at 35° in open MBO and 0.50±0.27 N•m/deg at 40° in arthroscopic MBO (Figure ​(Figure11). Figure 1 Ankle torque and stiffness during inversion test during open and arthroscopic MBO In this study, biomechanical analysis was performed for operations of CAI and there was no statistically significance in torque and stiffness. In comparison to open MBO, arthroscopic MBO is good alternative technique for CAI.

In recent decades, there has been an increasing interest in the use of robotic powered exoskeletons to assist patients with movement disorders in rehabilitation and daily life. Providing assistive torque that compensates for the user's remaining muscle contributions is a growing and challenging field within exoskeleton control. In this article, ankle joint torques were estimated using electromyography (EMG)-driven neuromusculoskeletal (NMS) model and an artificial neural network (ANN) model in seven movement tasks, including fast walking, slow walking, self-selected speed walking, and isokinetic dorsi/plantar flexion at 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /s and 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /s. In each method, EMG signals and ankle joint angles were used as input, the models were trained with data from 3-D motion analysis, and ankle joint torques were predicted. Six cases using different motion trials as calibration (for the NMS model)/training (for the ANN) were devised, and the agreement between the predicted and measured ankle joint torques was computed. We found that the NMS model could overall better predict ankle joint torques from EMG and angle data than the ANN model with some exceptions; the ANN predicted ankle joint torques with better agreement when trained with data from the same movement. The NMS model predicted ankle joint torque best when calibrated with trials during which EMG reached maximum levels, whereas the ANN predicted well when trained with many trials and types of movements. In addition, the ANN prediction may become less reliable when predicting unseen movements. Detailed comparative studies of methods to predict ankle joint torque are crucial for determining strategies for exoskeleton control.

Lower leg muscle activation during the ebbets foot drills

In this study, kinetic analysis system of pedaling mechanism was investigated to evaluate pedaling efficiency using lower limbs model. This system was composed of evaluation program for calculation for joint torque of lower limbs. The lower libs model consisted of three segments, the thigh, the lower thigh and the foot. From the lower limbs model, all position of lower limb segments and joint torques were calculated. Additionally, the relationship between the ankle angle and normal force was proposed. This relationship does not require the image-analysis software with the high-speed camera.