Tibialis Anterior Muscle Activity Research Articles

Effects of Raised Heel Insole on Muscle Activity during ankle Sudden Inversion in Normal Adults

Raised heel insoles increase the plantar flexion angle of the ankle and cause ankle inversion sprain. The purpose of this study was to artificially create an ankle sudden inversion situation, which is a mechanical situation of actual ankle joint damage, and investigate the effect of the raised heel insole on ankle joint muscle activity. The subjects of this study were forty subjects with normal adults. The subjects performed sudden ankle inversion on the trapdoor with no raised heel insole, insole heights of 3cm, and insole heights of 7cm. The application of the raised heel insole was conducted randomly. The subjects performed the trapdoor test three times using dominant feet with a 60-second rest period between tests. This study assessed muscle activity during sudden ankle inversion three times. Raised heel insoles showed a significant decrease in Tibialis Anterior, Peroneus Longus, and Peroneus Brevis muscle activity than no raised heel insole (p<.05). Raised heel insoles showed a significant increase in Gastrocnemius muscle activity than no raised heel insole (p<.05). Raised heel insoles increase the risk of ankle sprain injury by reducing tibialis anterior and peroneus muscle activity during sudden ankle inversion.

Kinetic changes of gait initiation in individuals with chronic ankle instability: A systematic review.

Gait initiation (GI) in individuals with chronic ankle instability (CAI) has shown differences in the center of pressure (COP) and muscular measures compared to healthy controls. Some studies reported that these alterations appeared when GI was with the affected leg, while others indicated that they occurred when GI was with the non-affected leg. This systematic review aimed to understand kinetic and muscular differences between individuals with CAI, healthy controls, and the affected and non-affected legs of individuals with CAI. PubMed, Science Direct, Web of Science, Google Scholar, and Scopus databases (1990-2023) were searched using the Population, Exposure, Comparator, and Outcome measure. The PRISMA guidelines were followed. The outcome measures were the peak and rate of COP displacement in the medial-lateral and anterior-posterior directions, and resultant plane during phases 1, 2, and 3 of COP trace during GI and the duration of each phase. The other measures included the onset time of the tibialis anterior and soleus muscle activity between individuals with CAI, healthy controls, and the affected and non-affected legs of the individuals with CAI. The studies' quality assessment was conducted based on the Strengthening the Reporting of Observational Studies in Epidemiology checklist. Five studies were included in the final evaluation. The results of included studies showed, individuals with CAI spent less time during phases 1 and 2, as well as a shorter peak of COP displacement in the lateral direction during phase 1 compared to healthy controls, regardless of whether the GI was with the affected or non-affected leg. Individuals with CAI have probably adopted a strategy involving adjusting the peak of COP displacement to manage internal sway while in a single-leg stance. Overall, there was no comprehensive conclusion about differences between the two legs in individuals with CAI.

Postural control strategies with alterations in visual input conditions in a standing position.

Mediated by balance systems, postural control relies heavily on visual input. However, the precise relationship between various visual conditions and postural strategies for balance remains unclear. This study investigated alterations in the center of pressure (COP) and ankle muscle activity during standing positions in healthy individuals under different visual conditions. Fifty-three healthy university students participated in the study. Stabilometry was conducted to evaluate the total path length and outer circumferential area for the COP. Further, surface electromyography was utilized to assess the activity of the bilateral tibialis anterior (TA) and lateral head of gastrocnemius muscles. Participants were instructed to maintain an upright posture under three visual conditions: binocular (eyes open) and monocular (either closing the dominant or nondominant eye). The three conditions were compared using a one-way analysis of variance. No significant differences were observed in the COP across visual conditions. However, in the TA of the nondominant leg, the mean values for the binocular, dominant eye, and nondominant eye conditions were 0.91, 1.08, and 1.14 times that of the resting standing position. Notably, the TA of the nondominant leg was significantly lower in the binocular condition than the dominant and nondominant eye conditions. The study findings indicate that the COP remain consistent despite variations in external visual input. This stability is likely maintained through compensatory adjustments, such as increased TA muscle activity in the nondominant leg under the nondominant eye condition. These observations highlight the complex interplay between the visual perception and postural stability.

Effect of Foot Position on Ankle Muscle Activity During Wobble Board Training in Individuals With Chronic Ankle Instability

ObjectiveThe purpose of this study was to compare the effects of foot positioning on muscle activities of the peroneus longus (PL), medial gastrocnemius (MG), and tibialis anterior (TA)/PL ratio in individuals with chronic ankle instabilities (CAI) during wobble board training. MethodsThirty individuals with CAI were included, and statistical significance of PL and MG muscle activities was determined using 1-way repeated measures analysis of variance alongside TA/PL activity ratio at the university research laboratory. The participants performed the wobble board training in 3 different foot positions: medial from the centerline of the wobble board (WBT-M), middle from the centerline of the wobble board, and lateral from the centerline of the wobble board (WBT-L). Peroneus longus, MG, and TA muscle activities were measured using surface electromyography. ResultsPeroneus longus activity was significantly higher in the WBT-L position than in the other 2 positions, and it was significantly higher in the middle from the centerline of the wobble board than in the WBT-M position. Medial gastrocnemius activity was significantly greater in the WBT-L position than in the other 2 positions. Tibialis anterior/PL ratio was higher in the WBT-M position than in the other 2 positions. ConclusionThe findings of this study showed that WBT-L increased PL muscle activity by >70% of the maximal voluntary isometric contraction without increasing TA/PL ratio in individuals with CAI.

Assistive Technology for Real-Time Fall Prevention During Walking: Evaluation of the Effect of an Intelligent Foot Orthosis

Abstract We present an intelligent foot orthosis (IFO) designed to prevent lateral falls during walking by employing a magnetorheological (MR) fluid brake. This study aims to demonstrate the feasibility of evaluating effectiveness of the proposed orthosis in fall prevention. Seventeen healthy adults underwent four conditions: (1) without IFO, (2) with IFO and current-OFF, (3) with IFO current-ON, and (4) with IFO and control-ON. Gait was assessed by three-dimensional motion capture and with ground reaction force. Postural changes on the frontal plane were measured, and the mediolateral center of gravity and center of pressure inclination angle (ML COG-COP IA) was calculated. Additionally, tibialis anterior (TA) and peroneus longus (PL) muscle activity during walking were measured using surface electromyography. Results indicate a significant increase in ML COG-COP IA in (3). No significant differences were found in muscle activity between conditions. The study suggests that the posture's deviation from the lateral fall direction in (3) is primarily due to wearing the IFO, emphasizing human postural control over muscle activity. A negative correlation between ML COG-COP IA and TA muscle activity under (4), implies that individuals with lower TA muscle activity may benefit more from IFO fall prevention. In conclusion, the study demonstrates the feasibility of preventing lateral falls in human walking using the proposed orthosis with an MR fluid brake. The general efficacy of the orthosis in lateral fall prevention is suggested, emphasizing the need for further development.

BIOMECHANICAL INFLUENCE OF RUNNING SHOES WITH MIDSOLE HOLLOW STRUCTURE ON LOWER LIMBS DURING RUNNING

The objective was to investigate the effects of running shoes with midsole hollow structure span and height on the biomechanics of the lower limbs during running. We collected 21 adults with running habits who wore two pairs of running shoes with different midsole hollow structures and ran at a speed of 3.3[Formula: see text]m/s on a force-measuring treadmill. The lower limb kinematics, ground reaction force (GRF) and lower limb muscle activation characteristics were simultaneously captured by a motion capture system, a 3D force treadmill, and a surface electromyography (sEMG) system. Paired t-tests were performed on data for the two shoe conditions that fit the normal distribution assumptions; otherwise, Wilcoxon signed-rank tests were used. The statistical parameter mapping (SPM) technology was used for the analysis of 1D parameters of kinematic, dynamic, and sEMG activation characteristics. The result showed that the time to the peak impact force at touchdown of Hollow shoe2 was significantly increased ([Formula: see text]), the maximum loading rate ([Formula: see text]) and average loading rate ([Formula: see text]) were significantly reduced, braking time ([Formula: see text]), push time ([Formula: see text]), contact time ([Formula: see text]) of Hollow shoe2 were significantly increased compared with Hollow shoe1. Hollow shoe2 push phase of the tibialis anterior muscle activation characteristics was significantly lower (SPM, [Formula: see text]) than Hollow shoe1. Our conclusion is that running shoes offer the solution as they have the advantage of the complex structure of the hollow midsole.

Effect of Forward Reaching With a Modified Sitting Position on Muscle Contraction in the Paretic Lower Extremity of Individuals in the Early Sub-Acute Phase of Stroke: A Randomized Control Trial.

Introduction Forward reaching in sittinghas been shown to facilitate muscle contraction in the paretic lower limb of stroke survivors. Change in the sitting surface has been shown to alter the contribution of lower extremity muscles to maintain postural control. This study investigated the effect of forward reaching in a modified sitting position on the paretic lower extremity muscles of patients with stroke. Methods First-time cerebral stroke survivors in their early sub-acute phase were randomly allocated to the experimental or control group. The experimental group engaged in training sessions focusing on reaching a target while seated with only the paretic foot placed on a support, whereas the control group performed the same task with both feet supported on the surface. Each group completed three sets of 10 repetitions of forward reaching for eight days as a part of the training. Quadriceps and tibialis anterior muscle activity in the paretic leg were measured using surface electromyography before the first and after the last session of intervention. Statistical analysis was conducted using parametric tests with a significance level set at p < 0.05. Results Sixty-three subjects completed the study, with 31 in the experimental group and 32 in the control group. The results of the post-intervention analysis indicated a statistically significant increase in the EMG activity of the tibialis anterior and quadriceps muscle surfaces in both groups (p < 0.001). Notably, the experimental group exhibited significantly higher muscle activity in both quadriceps and tibialis anterior compared to the control group (p < 0.001). Conclusion Forward reaching with only the paretic lower limb grounded effectively improves quadriceps and tibialis anterior muscle recruitment in the early sub-acute phase of stroke.

Analysis of stress response distribution in patients with lateral ankle ligament injuries: a study of neural control strategies utilizing predictive computing models.

Ankle sprains are prevalent in sports, often causing complex injuries to the lateral ligaments. Among these, anterior talofibular ligament (ATFL) injuries constitute 85%, and calcaneofibular ligament (CFL) injuries comprise 35%. Despite conservative treatment, some ankle sprain patients develop chronic lateral ankle instability (CLAI). Thus, this study aimed to investigate stress response and neural control alterations during landing in lateral ankle ligament injury patients. This study recruited twenty individuals from a Healthy group and twenty CLAI patients performed a landing task using relevant instruments to collect biomechanical data. The study constructed a finite element (FE) foot model to examine stress responses in the presence of laxity of the lateral ankle ligaments. The lateral ankle ligament was modeled as a hyperelastic composite structure with a refined representation of collagen bundles and ligament laxity was simulated by adjusting material parameters. Finally, the validity of the finite element model is verified by a high-speed dual fluoroscopic imaging system (DFIS). CLAI patients exhibited earlier Vastus medialis (p < 0.001) and tibialis anterior (p < 0.001) muscle activation during landing. The FE analysis revealed that with laxity in the ATFL, the peak von Mises stress in the fifth metatarsal was 20.74MPa, while with laxity in the CFL, it was 17.52MPa. However, when both ligaments were relaxed simultaneously, the peak von Mises stress surged to 21.93MPa. When the ATFL exhibits laxity, the CFL is subjected to a higher stress of 3.84MPa. Conversely, when the CFL displays laxity, the ATFL experiences a peak von Mises stress of 2.34MPa. This study found that changes in the laxity of the ATFL and the CFL are linked to shifts in metatarsal stress levels, potentially affecting ankle joint stability. These alterations may contribute to the progression towards CLAI in individuals with posterolateral ankle ligament injuries. Additionally, significant muscle activation pattern changes were observed in CLAI patients, suggesting altered neural control strategies post-ankle ligament injury.

Modelling of impulse activity of afferent fibers of antagonist muscles during transcutaneous electrical stimulation of the spinal cord during walking

The article describes the results of studies on the impulse activity of various groups of afferent fibers and EMG patterns of lower leg antagonist muscles when walking without, during and after transcutaneous electrical stimulation of the dorsal roots of the lower thoracic spinal cord of a person. Using a mathematical model based on the prediction of the triggering of muscle spindles, variability in the manifestation of impulse activity of various afferents tibialis anterior muscle (TA) and gastrocnemius medialis muscle (GM) when walking under different experimental conditions is shown. It was found that walking on a movable treadmill tape in the absence of spinal cord stimulation was accompanied by strong impulse activity of afferents I (Ia and Ib) and II groups GM, increased excitability of its motorneuron pool and weakening of afferent activity and excitability of TA. On the contrary, electrical stimulation of the spinal cord during walking caused strong impulsive activity of group II TA afferents and moderate — GM, while the activity of Ia fibers TA and GM decreased to moderate impulsivity, Ib afferents of the same muscles had the weakest activity, and the excitability of the GM motorneuron pool was greater than TA. During the postactivation period, walking was accompanied by increased impulses of afferent fibers of group Ib and II GM, weakening of afferent flows of Ib TA and Ia afferents GM, but along with this, afferent signals of group Ia and II to the motorneuron nucleus TA decreased to moderate impulses, and excitability of the motorneuron pool GM was higher than TA. The supposed reflex mechanisms of locomotion regulation are discussed on the basis of well-known phenomena associated with the interaction of various afferent inputs to the spinal cord neuronal apparatus in the system of lower leg antagonist muscles.

Evacuation safety effects of a lightweight elevator-type evacuation device using carbon material: Focus on plantar pressure and muscle strength.

Elevator-type evacuation devices have proven to be feasible in high-rise buildings through studies on safety performance and evacuation time. However, there is a lack of research on safety using biosignal analysis in the elderly population. A carbon material is used in this study to reduce the weight of an evacuation elevator. The impact on the human body is evaluated by conducting a satisfaction survey involving elderly and youth groups and quantitatively analyzing biological signals, including electromyography (EMG) and plantar pressure, during five repeated uses of the proposed device. The study involves 12 healthy adults in their 20s and 20 elderly individuals with no experience in using an evacuation elevator. The EMG and left and right plantar pressures are analyzed to evaluate the physical factors affected by repeated use. The experiment results showed that the normalization of EMG to maximum voluntary contraction showed a significant decrease with repeated use, especially in the right tibialis anterior muscle. Moreover, plantar pressure shows a significant difference, which decreased with repetition, and the left and right balance gradually tilted to the left. This suggests that with more repeated use, muscle tension decreases owing to adaptation, resulting in lower muscle activity and plantar pressure. Particularly, the tibialis anterior muscle experiences significant muscle activity, indicating increased load, but without any apparent danger. In the future, it will be necessary to evaluate elevators for disabled individuals.

Effect of soft tissue, range of motion and muscle strength on deep squatting

The purpose was to clarify the effects of soft tissues such as muscles and fat, range of motion of the hip, knee and ankle, knee extension and ankle dorsiflexion muscle strength and muscle activity on deep squatting. The participants were 18 healthy university students. Physical characteristics, circumference, subcutaneous fat thickness, and range of motion were measured. After that, they performed deep squatting and lower limb muscle strength was measured. Muscle activities in lower limb during performance was also measured. Statistical tests were performed on the differences between the able group and the unable group, with each item as the dependent variable. Body weight, BMI, abdominal circumference, and tibialis anterior muscle activity were significantly lower in the able group (able to perform a deep squat), than in the unable group. Additionally, range of motion of the hip flexion and ankle dorsiflexion were significantly higher in the able group than in the unable group. It was clarified that soft tissues characteristics are connected to deep squatting in addition to range of motion.

Treadmill running: how long before soft-tissue vibrations reach a steady state?

The aim of this study was to determine whether a steady state was reached over time in soft-tissue vibrations (STV) when running with different midsole hardness. Kinematics, kinetics and electromyography changes were also investigated in an attempt to be as comprehensive as possible. Forty-five physically active adults (17 females) with experience in treadmill running performed an 8.5 minutes trial at a self-selected speed with soft, medium and hard midsoles. STV of gastrocnemius muscle, kinetics, kinematics and electromyographic activity of gastrocnemius muscle and tibialis anterior were recorded for 30 seconds at minutes 0, 2, 4, 6 and 8. No time effects were found for STV, passive peak, loading rate and leg muscle activity. No significant footwear × time interactions were observed, suggesting that familiarisation is independent of midsole hardness. The fastest adjustments were an increase of foot inversion and active peak within the first 4 minutes respectively before reaching a steady state. Step frequency and vertical stiffness decreased and plateaued at minute 6. Duty factor and contact time increased whereas flight time decreased during the entire running trial. Results indicate that a familiarisation to midsole hardness is not needed for STV reliable measurements. Depending on the other biomechanical parameters assessed, we recommend at least a 6-minute running trial and a longer running trial for contact and flight times assessment.

Immediate Effect of a Comprehensive Foot Mobility and Strengthening Treatment on Ankle Muscle Activation in Children with Spastic Diplegia

Foot mobility and strengthening treatment (FMST) is a routinely practiced management strategy in musculoskeletal rehabilitation to improve ankle and foot alignment and muscle function, which prevents joint deformities. The FMST may contribute to improvements in foot alignment and muscle function in children with cerebral palsy (CP). However, treatment influence on muscle imbalances and strength in children with spastic diplegic CP is not yet documented. The aim of the study was to determine the effect of FMST on tibialis anterior (TA), medial gastrocnemius (MG), peroneus longus (PL), and soleus muscle activity using electromyography (EMG) in children with spastic diplegic CP. Twenty children with spastic diplegia (mean age: 7.4 years) with GMFCS levels I, II and III were included in this pre and post-experimental (preliminary) study. Muscle activation of TA, MG, PL, and soleus was recorded using surface EMG in a standing position before and after providing the intervention. Muscle activation in RMS-EMG (mV) was calculated. Findings showed a significant increase in muscle activation of TA, MG, and PL in standing position following the intervention. The increase in soleus muscle activation in standing was not statistically significant. We hypothesized that FMST could alter the muscle recruitment pattern. Our findings showed immediate improvement in muscle activation after the intervention. Future studies should consider its carryover effect on motor performance and gait using functional outcomes.

Ankle Biomechanics During Multidirectional Landings in Athletes With Chronic Ankle Instability.

Assessing and understanding the control of the ankle during multidirectional jump landings in athletes with chronic ankle instability (CAI) would help health professionals develop interventions to reduce the risk of recurrent injuries. The aim of this study was to investigate the angle, angular velocity, and movements of the ankle joint, and the muscle activity of peroneus longus (PL), tibialis anterior (TA), and gastrocnemius (GAS) muscles during multidirectional landings in athletes with CAI. Nineteen athletes with CAI (≤25 Cumberland Ankle Instability Tool-Thai Score) participated. A Vicon Nexus motion analysis system synchronously collected data with an AMTI force plate and surface electromyography (EMG) to capture kinematics, kinetics, and muscle activity, respectively. Participants were asked to perform single-leg jump-landing tests in forward (0°), 30° diagonal, 60° diagonal, and lateral (90°) directions. Ankle joint kinematics, kinetics, and muscle activity of PL, TA, and GAS were analyzed. Repeated measure ANOVA (analysis of variance) and Friedman tests were used to analyze the main effects of the jump-landing direction. Athletes with CAI exhibited significant differences in ankle angles, angular velocities, ankle movements, and average muscle activity of GAS between directions. Greatest average EMG of GAS muscle was observed during landing in the lateral direction compared with the forward and 30° diagonal directions. Lateral and diagonal direction movements showed the greatest risks associated with recurrent ankle sprains. Impairments of neuromuscular control in both pre-landing and landing phases were observed in athletes with CAI when considered alongside previously published data. Laboratory-based observational study.

The Accuracy of Ankle Eccentric Torque Control Explains Dynamic Postural Control During the Y-Balance Test.

The Y-Balance Test (YBT), especially the posteromedial (PM) reach direction (PM-YBT), is able to identify dynamic postural control deficits in those who have ankle instability. However, there still exists a need to understand how sensorimotor function at the ankle explains the performance during the PM-YBT. The purpose of this study was to determine whether the ability to accurately control eccentric ankle torque explained PM-YBT performance. It was hypothesized that eccentric dorsiflexion/plantarflexion torque control would be positively related to the maximum reach distance (MRD) of PM-YBT. Cross-sectional study. Twelve healthy subjects performed the PM-YBT, maximum voluntary isometric contractions (MVIC) for both dorsiflexion and plantarflexion muscle strength, and then the torque control testing of the ankle. The torque control testing provided a target torque level on a screen in front of the subject and passive rotations of the ankle joint in the sagittal plane at 10 deg/sec between plantarflexion to dorsiflexion. Subjects were then instructed to eccentrically contract the dorsiflexors and plantar flexors to generate torque while the ankle joint rotated. The accuracy of torque control during eccentric dorsiflexion and plantarflexion by calculating absolute errors, the area between the target torque and the produced torque were evaluated. Tibialis anterior and soleus muscle activities were simultaneously recorded during testing. A step-wise linear regression model was used to determine the best model predicted the MRD of the PM-YBT (PM-MRD). A step-wise linear regression developed a model explaining only eccentric dorsiflexion torque control predicted higher PM-MRD score (R2 = 44%, F1,10 = 7.94, β = -0.67, p = 0.02). The accuracy of torque control during eccentric dorsiflexion predicts better performance in the PM-YBT. 3b.

Judokas Exhibit Short Response Latency Even to Non-Judo-Specific External Perturbation: Insights Into the Involuntary Postural Control Ability in Humans.

Humans experience unanticipated external postural perturbations and recover their posture faster via involuntary responses than voluntary responses. Previous cross-sectional comparisons between athletes and untrained populations have suggested that daily motor experiences can lead to adaptations in the reflex system, but the temporal aspect of this adaptation has been unclear. Here we show that judokas have an earlier muscle activation response to even non-judo-specific external perturbations compared with an untrained population. The response latency to a backward push-and-release type postural perturbation was compared between male judokas (n = 7, career >13years, ranging from world champions to prefectural competitors) and untrained nonjudokas (n = 7). Latency was defined as the instant of tibialis anterior muscle activity onset. Judokas exhibited shorter latency (20.6 ± 7.1ms) than nonjudokas (28.3 ± 8.9ms). The rank order of latency in judokas did not correlate with their competition performance. We suggest that daily training in responding to perturbations might improve some parts of the sensorimotor pathway relating to postural response latency, and that this excellence in involuntary response is independent of athletic performance. The findings provide a novel perspective for understanding postural control ability in humans.

Effects of jaw clenching on dynamic reactive balance task performance after 1-week of jaw clenching training.

Good balance is essential for human daily life as it may help to improve the quality of life and reduce the risk of falls and associated injuries. The influence of jaw clenching on balance control has been shown under static and dynamic conditions. Nevertheless, it has not yet been investigated whether the effects are mainly associated with the dual-task situation or are caused by jaw clenching itself. Therefore, this study investigated the effects of jaw clenching on dynamic reactive balance task performance prior to and after 1 week of jaw clenching training. It was hypothesized that jaw clenching has stabilizing effects resulting in a better dynamic reactive balance performance, and these effects are not related to dual-task benefits. A total of 48 physically active and healthy adults (20 women and 28 men) were distributed into three groups, one habitual control group (HAB) and two jaw clenching groups (JAW and INT) that had to clench their jaws during the balance tasks at T1 and T2. One of those two groups, the INT group, additionally practiced the jaw clenching task for 1 week, making it familiar and implicit at T2. The HAB group did not receive any instruction regarding jaw clenching condition. Dynamic reactive balance was assessed using an oscillating platform perturbed in one of four directions in a randomized order. Kinematic and electromyographic (EMG) data were collected using a 3D motion capture system and a wireless EMG system, respectively. Dynamic reactive balance was operationalized by the damping ratio. Furthermore, the range of motion of the center of mass (CoM) in perturbation direction (RoMCoM_AP or RoMCoM_ML), as well as the velocity of CoM (VCoM) in 3D, were analyzed. The mean activity of the muscles relevant to the perturbation direction was calculated to investigate reflex activities. The results revealed that jaw clenching had no significant effects on dynamic reactive balance performance or CoM kinematics in any of these three groups, and the automation of jaw clenching in the INT group did not result in a significant change either. However, high learning effects, as revealed by the higher damping ratio values and lower VCoM at T2, were detected for the dynamic reactive balance task even without any deliberate balance training in the intervention phase. In the case of backward perturbation of the platform, the soleus activity in a short latency response phase increased for the JAW group, whereas it decreased for HAB and INT after the intervention. In the case of forward acceleration of the platform, JAW and INT showed a higher tibialis anterior muscle activity level in the medium latency response phase compared to HAB at T1. Based on these findings, it can be suggested that jaw clenching may lead to some changes in reflex activities. However, the effects are limited to anterior-posterior perturbations of the platform. Nevertheless, high learning effects may have overall overweighed the effects related to jaw clenching. Further studies with balance tasks leading to less learning effects are needed to understand the altered adaptations to a dynamic reactive balance task related to simultaneous jaw clenching. Analysis of muscle coordination (e.g., muscle synergies), instead of individual muscles, as well as other experimental designs in which the information from other sources are reduced (e.g., closed eyes), may also help to reveal jaw clenching effects.

Physiological characterization of instrumental learning in the spinal cord using the Paw Withdrawal Learning paradigm

Following spinal cord injury (SCI), sensory and motor functions are severely disrupted yet the spinal circuitry below the injury site continues to maintain active and functional neuronal properties (Edgerton, 2004). The spinal cord is endogenously capable of several forms of adaptive plasticity, including functional re-training with exercise, instrumental, and Pavlovian learning. The paw withdrawal learning (PaWL) paradigm represents a simple spinal instrumental learning model (Jindrich 2019). Briefly, in mice whose spinal cords are completely transected (ST) at mid-thoracic (T7-T9) level, the tibialis anterior (TA) muscle is given a sub maximal threshold shock to a hind leg when the leg is extended below a 1mm imposed threshold from a baseline starting position. The contingent group mice learn to maintain the shocked leg, in a flexed position while the experimentally coupled noncontingent group of mice do not acquire the flexed position. To demonstrate the acquisition of the flexed paw hold is mediated through muscle-specific proprioceptive inputs and a time dependent modification of the spinal interneuronal network associated with the TA motor pool, we measured the TA muscle activity using acute EMG during PaWL in both Contingent stim and non-contingent stim groups. To demonstrate that TA specific sensory afferents are critical in PaWL, we blocked the proprioceptive muscle and the cutaneous afferents using Lidocaine. During PaWL, the TA muscle showed significant EMG activity when compared to medial gastrocnemius and vastus lateralis muscles. We detected greater TA muscle activity in the Contingent stim compared to the non-contingent groups. The significant increase in the EMG amplitude in the TA muscle and time-frequency and power relationships in the contingent group, but not the non-contingent group, suggests that the successful learning requires a temporal engagement of the spinal sensorimotor network. CSULA Mini-Grant 2020 and Joseph/Gomez-Pinilla R01NS056413 (Diversity Supplement) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Fascicle dynamics of the tibialis anterior muscle reflect whole-body walking economy

Humans can inherently adapt their gait pattern in a way that minimizes the metabolic cost of transport, or walking economy, within a few steps, which is faster than any known direct physiological sensor of metabolic energy. Instead, walking economy may be indirectly sensed through mechanoreceptors that correlate with the metabolic cost per step to make such gait adaptations. We tested whether velocity feedback from tibialis anterior (TA) muscle fascicles during the early stance phase of walking could potentially act to indirectly sense walking economy. As participants walked within a range of steady-state speeds and step frequencies, we observed that TA fascicles lengthen on almost every step. Moreover, the average peak fascicle velocity experienced during lengthening reflected the metabolic cost of transport of the given walking condition. We observed that the peak TA muscle activation occurred earlier than could be explained by a short latency reflex response. The activation of the TA muscle just prior to heel strike may serve as a prediction of the magnitude of the ground collision and the associated energy exchange. In this scenario, any unexpected length change experienced by the TA fascicle would serve as an error signal to the nervous system and provide additional information about energy lost per step. Our work helps provide a biomechanical framework to understand the possible neural mechanisms underlying the rapid optimization of walking economy.

Delayed response in rectus abdominis muscle following a step perturbation in subjects with and without recurrent low back pain.

Delayed trunk and lower limb muscle activation is associated with balance loss and fall injuries in subjects with recurrent low back pain (LBP). This study was conducted to compare differences in the onset of muscle contractions of the trunk and lower limb muscles following a treadmill-induced step perturbation between subjects with and without LBP. Eighty-three right limb dominant individuals (43 subjects with LBP and 40 control subjects) were exposed to the perturbation (0.31m/s velocity for 0.2m). The electromyography (EMG) reaction times were analyzed during the first step following the perturbation. The EMG electrodes were placed on both sides of the trunk and lower limbs, including the rectus abdominis (RA), erector spinae (ES), tibialis anterior (TA), and gastrocnemius (GA) muscles. The group x muscle interaction was statistically significant (F = 9.44, p = 0.003). The TA muscle activation was significantly delayed compared to the RA, ES, and GA. There was a significant interaction on side x muscle (F = 4.14, p = 0.04). The RA muscles were significantly delayed on the non-dominant (t = -3.35, p = 0.001) and dominant (t = -2.53, p = 0.01) sides in the LBP group. The LBP group demonstrated a delayed reaction time on the RA muscles, which indicated poor trunk control relative to the lower limbs. The delayed bilateral RA muscle might indicate possible coordination problems relative to the ES and lower limb muscles, which may lead to potential fall hazards.