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This study aimed to develop and evaluate the reliability of a surface electromyography-based (sEMG) index to quantify knee muscle coactivation in healthy recreational athletes during the Lower Quarter Y-Balance Test (YBT-LQ). A prospective observational repeated measures design was used to assess both intra- and inter-rater reliability. Forty males completed three trials, with two raters independently conducting assessments. sEMG signals from the vastus medialis, vastus lateralis, biceps femoris, and semitendinosus muscles were collected to calculate four coactivation indices (CoAIs) for different muscle pairs. The reliability evaluation of these CoAIs was based on intraclass correlation coefficients. The results revealed that the reliability of the CoAIs varied depending on the muscle pair, direction, and limb examined. The highest intra- and inter-rater reliability was noted for the left lower limb in the posterolateral direction. The lowest reliability was found for the right lower limb in the anterior direction. Statistical analyses indicated significant differences in specific CoAIs across different YBT-LQ directions. These findings highlight the potential of sEMG-based CoAIs for assessing knee muscle activity during the YBT-LQ in healthy male recreational athletes. However, choosing CoAIs is critical for reliable clinical and research assessments of knee stability and neuromuscular control. [ABSTRACT FROM AUTHOR]

Research suggests mechanical changes occur to the body over the course of the day including shrinking of the intervertebral disc height which can increase rotational stiffness and rigidity of the spinal column. Further, pain sensitivity has been observed to fluctuate throughout the day, suggesting variations in pain sensitivity. Previous work has identified biomechanical and neuromuscular features related to the development of musculoskeletal pain during prolonged standing; however, many protocols have not controlled for time of day. Does the time of day (i.e., diurnal variation) have an effect on the common neuromuscular and biomechanical variables characterizing the development of standing musculoskeletal pain in a two-hour prolonged standing protocol? A convenience sample of 20 healthy young adults (10 female and 10 male) completed two 2-hour prolonged standing bouts (8:00 a.m. and 8:00 p.m.) on separate days. Visual analogue scales were used to measure pain perception of the low back, legs, and feet throughout each protocol. Neuromuscular control was measured using surface EMG on muscles of the trunk and lower extremities. Postural sway was captured using measures of joint range of motion, and the analysis of center of pressure trajectory data using a force plate. Diurnal variation was observed to influence the development of musculoskeletal pain. Specifically, pain perception was found to be increased in the evenings as more participants were classified as pain developers in the PM sessions, and mean leg and foot pain perceptions were higher in the evening. Reduced postural sway patterns, and elevated co-contraction indices were found to be associated with the development of pain. These results suggest that future research assessing standing-pain protocols should control for time of day. Additionally, further research is warranted to explore the mechanistic causes of the development of standing pain. • Diurnal variation found to impact standing-induced discomfort. • Pain perceptions observed to be higher in the evening. • Lower sway parameters associated with standing-induced discomfort. • Co-contraction indices associated with standing-induced discomfort. • Future research using a standing pain protocol should control for time of day. [ABSTRACT FROM AUTHOR]

Excessive muscle co-contraction is one of the factors related to the progression of knee osteoarthritis (OA). A previous study demonstrated that pain, joint instability, lateral thrust, weight, and lower extremity alignment were listed as factors affecting excessive co-contraction in knee OA. However, this study aimed to assess the association between fear-avoidance beliefs and muscle co-contraction during gait and stair climbing in people with knee OA. Twenty-four participants with knee OA participated in this cross-sectional study. Co-contraction ratios (CCRs) were used to calculate muscle co-contraction during walking and stair climbing, using surface electromyography. Fear-avoidance beliefs were assessed by the Tampa Scale for Kinesiophobia-11 (TSK-11) for kinesiophobia and the Pain Catastrophizing Scale (PCS) for pain catastrophizing. Secondary parameters that may influence co-contraction, such as degree of pain, lateral thrust, weight, and lower extremity alignment, were measured. The relationships between the CCR during each movement, TSK-11, and PSC were evaluated using Spearman's rank correlation coefficient and partial correlation analysis, adjusted by weight and lower extremity alignment. Partial correlation analysis showed a significant correlation only between medial muscles CCR and TSK-11 during stair descent (r = 0.54, p < 0.05). Our study revealed that kinesiophobia could be associated with co-contraction during stair descent in people with knee OA. [ABSTRACT FROM AUTHOR]

Restrictions to control the COVID-19 pandemic have caused older adults to stop their usual activities, including physical exercises. The novel approach of isometric no-load resistance training (NLRT) can be an interesting alternative to conventional training to oppose the harmful effects of detraining. We described the design and preliminary evaluation of an eight-week, twice-weekly NLRT program for older adults returning to strength training programs after COVID-19 lockdown. An older woman (66 years, 61.9kg, 158.5cm) and an older man (66 years, 84.1kg, 166.5cm) who were engaged in conventional strength training programs before the first COVID-19 lockdown participated in this case study. We collected muscle thickness measures using a B-mode ultrasound imaging and maximum isometric torque using an isokinetic dynamometer. Our results revealed that NLRT seems to be a good alternative to increase muscle thickness of knee and elbow flexors and extensors muscles in older adults. However, NLRT effects were inconsistent for maximum torque. [ABSTRACT FROM AUTHOR]

During upright standing, individuals often use co-contraction muscle activity at the ankle joint when encountering increased postural difficulty; however, this strategy has been shown to be maladaptive. The purpose of the current investigation was to examine the effect of sloped standing on postural sway and muscle co-contraction at the ankle joint as a function of postural difficulty. Twelve young (21.67 ± 1.11 years) adults performed upright standing on flat, declined, and inclined support surfaces. Center of pressure displacements indexed postural sway while electromyography data were collected for the tibialis anterior and gastrocnemius medialis muscles. A co-contraction index and a nonlinear coupling metric (cross-approximate entropy) were computed between ankle dorsiflexor and plantar flexor muscles (tibialis anterior/gastrocnemius medialis) activity. The results showed that higher degrees of postural difficulty led to increased amounts of sway as well as increased sway regularity. Lower co-contraction index was observed for higher degrees of postural difficulty; however, increased dynamic coupling occurred with deviations from the flat standing condition. Overall, increased postural difficulty as manipulated by sloped standing (in either inclined or declined conditions) resulted in individuals adopting a more regular sway trajectory that may be due, in part, to a stronger dynamic coupling strategy occurring at the neuromuscular level. [ABSTRACT FROM AUTHOR]

The central nervous system uses muscle co-activation for body coordination, effector movement control, and joint stabilization. However, co-activation increases compression and shear stresses on the joints. Lifting activity is one of the leading causes of work-related musculoskeletal problems worldwide, and it has been shown that when the risk level rises, lifting enhances trunk muscle co-activation at the L5/S1 level. This study aims to investigate the co-activation of lower limb muscles during liftings at various risk levels and lifting types (one-person and vs. two-person team lifting), to understand how the central nervous system governs lower limb rigidity during these tasks. The surface electromyographic signal of thirteen healthy volunteers (seven males and six females, age range: 29–48 years) was obtained over the trunk and right lower limb muscles while lifting in the sagittal plane. Then co-activation was computed according to different approaches: global, full leg, flexor, extensor, and rostro-caudal. The statistical analysis revealed a significant increase in the risk level and a decrease in the two-person on the mean and/or maximum of the co-activation in almost all the approaches. Overall, our findings imply that the central nervous system streamlines the motor regulation of lifting by increasing or reducing whole-limb rigidity within a distinct global, extensor, and rostro-caudal co-activation scheme, depending on the risk level/lifting type. [ABSTRACT FROM AUTHOR]

Background and Aims Today, there is an argument about the effect of various stretching movements on the performance of athletes. Therefore, this study investigated the acute effect of static and dynamic stretching on muscle activity and co-contraction of scapular stabilizer muscles during pull-ups in gymnasts. Methods According to the inclusion and exclusion criteria, 15 professional gymnasts with a mean age of 23.25±2.57 years, height of 170.93±5.88 cm, and weight of 64.54±5.06 kg were selected as research samples and divided into three subgroups (each with 5 athletes). In the pre-test, subjects performed pullup activity, and muscle activities of the serratus anterior, upper trapezius, middle trapezius, and lower trapezius muscles were measured using a biometric electromyography device. Then, each subgroup performed a different stretching protocol in each session, and a post-test was conducted like the pretest. Repeated measures analysis of variance, the Bonferroni post hoc test, and the paired t test were used to test the study hypotheses. Results The results showed that static and dynamic stretching caused a significant decrease and increase in muscle activity in both concentric and eccentric phases, respectively. Also, the results showed that dynamic stretch caused a reduction in co-contraction of the serratus anterior and middle trapezius muscles in both concentric and eccentric phases. In addition, there is a significant difference between the effect of static and dynamic stretch and between dynamic stretch and control on the co-contraction of the serratus anterior and middle trapezius muscles in the concentric and eccentric phases. Conclusion The results showed that the co-contraction of the serratus anterior and middle trapezius muscles decreased after using dynamic stretching. Therefore, considering the importance of muscle cocontraction in the occurrence of shoulder joint injuries and preventing injuries in the shoulder joint of gymnasts, it is suggested that coaches and gymnasts use dynamic stretching exercises more carefully. [ABSTRACT FROM AUTHOR]

Aim: To investigate co-contraction in reinnervated elbow flexor muscles following a nerve transfer. Materials & methods: 12 brachial plexus injury patients who received a nerve transfer to reanimate elbow flexion were included in this study. Surface electromyography (EMG) recordings were used to quantify co-contraction during sustained and repeated isometric contractions of reinnervated and contralateral uninjured elbow flexor muscles. Reuslts: For the first time, this study reveals reinnervated muscles demonstrated a trend toward higher co-contraction ratios when compared with uninjured muscle and this is correlated with an earlier onset of muscle fatigability. Conclusion: Measurements of co-contraction should be considered within muscular function assessments to help drive improvements in motor recovery therapies. [ABSTRACT FROM AUTHOR]

Postural control is one of the primary body functions for fall prevention. Unexpected perturbation-based balance training is effective for improving postural control. However, the effect of perturbation-based training using assistive devices on muscle activity and co-contraction for standing balance is still unclear. This training is also difficult to perform easily because it requires large instruments or expert guidance. The purpose of this study is to demonstrate the effect of perturbation-based balance training using a wearable balance training device (WBTD) on postural control. In this study, fourteen healthy young adult males were assigned to either a WBTD group or a sham group. In the intervention session, participants in the WBTD group were perturbed either left or right direction at random timing by the WBTD during tandem stance balance training. Participants in the Sham group did not receive external perturbation during tandem stance balance training. Before and after the intervention session, participants of both groups underwent unexpected lateral perturbation postural control testing (pre- and post-test). The normalized integral of electromyography (IEMG), co-contraction index (CCI), and center of pressure (COP) parameters were measured in the pre- and post-test. Experimental results showed that the WBTD group in the post-test significantly decreased left Gluteus Medius IEMG, CCI of both Gluteus Medius, and peak $\text {COP}_{\text {ML}}$ velocity, compared to those of the pre-test ( ${p} \lt 0.001$ , ${p} \,\, =0.024$ , ${p} \,\, =0.031$ , respectively). We conclude that balance training using WBTD could improve flexible postural control adjustment via cooperative muscle activation.

This study aimed to develop and evaluate the reliability of a surface electromyography-based (sEMG) index to quantify knee muscle coactivation in healthy recreational athletes during the Lower Quarter Y-Balance Test (YBT-LQ). A prospective observational repeated measures design was used to assess both intra- and inter-rater reliability. Forty males completed three trials, with two raters independently conducting assessments. sEMG signals from the vastus medialis, vastus lateralis, biceps femoris, and semitendinosus muscles were collected to calculate four coactivation indices (CoAIs) for different muscle pairs. The reliability evaluation of these CoAIs was based on intraclass correlation coefficients. The results revealed that the reliability of the CoAIs varied depending on the muscle pair, direction, and limb examined. The highest intra- and inter-rater reliability was noted for the left lower limb in the posterolateral direction. The lowest reliability was found for the right lower limb in the anterior direction. Statistical analyses indicated significant differences in specific CoAIs across different YBT-LQ directions. These findings highlight the potential of sEMG-based CoAIs for assessing knee muscle activity during the YBT-LQ in healthy male recreational athletes. However, choosing CoAIs is critical for reliable clinical and research assessments of knee stability and neuromuscular control.

Promoting an erect posture in standing has been advocated to offer superior protection to the spine when compared to hyperlordotic and swayback postures. Do postural adjustments towards external perturbation differ between erect, hyperlordotic and swayback postures? If so, which posture offers better protection to lumbar spine? Forty-four healthy adults received top-down perturbations under unpredictable (without visual-and-auditory input) and predictable (with visual-and-auditory input) conditions in three simulated postures: erect, hyperlordotic, and swayback. Postural adjustments namely the centre of pressure parameters, joint angle onsets, and neuromuscular responses measured by muscle onsets and co-contraction between muscle pairs upon the perturbation were compared using the two-way repeated measures ANOVA. Post-hoc analysis with Bonferroni correction was conducted to identify the between-posture differences for the respective postural adjustment parameters. Path length, ellipse area and average velocity of centre of pressure were significantly greater under unpredictable condition as compared to predictable condition (p < 0.001). Significant between-posture difference was detected in centre of pressure path length (p < 0.035), pelvic tilt onset (p < 0.038) and all muscle co-contraction indexes (p < 0.001). Post-hoc analysis revealed significantly smaller centre of pressure path length in erect posture as compared to hyperlordotic and swayback postures (p < 0.01) under unpredictable conditions. Significantly greater co-contraction indexes of lumbar multifidus and erector spinae, and internal oblique and lumbar multifidus were found in hyperlordotic as compared to erect and swayback postures (p < 0.05). Compared to erect posture, adoption of hyperlordotic and swayback postures altered the contributions of the active and passive subsystems of the spine that regulates postural control upon external perturbations. Such differences in neuromuscular control may lessen the capacity of the human spine to withstand loading and shear forces. Prospective studies are required to validate if habitually adopted hyperlordotic and swayback postures contribute to an earlier/ higher prevalence of spinal dysfunctions. • Greater postural adjustment incurred under unpredictable than predictable perturbations. • Greater anteroposterior sway in swayback posture under unpredictable perturbations. • Higher co-contraction found in hyperlordotic posture. • Hyperlordotic and swayback postures impair lumbopelvic postural control efficacy. [ABSTRACT FROM AUTHOR]

Purpose: Over-pronated foot (OPF) is a common abnormality of the foot. Sand can change lower limb muscle activities. Therefore, the aim of this study was to evaluate the effect of a sand exercise program on knee muscle co-contraction in runners with OPF. Methods: Thirty individuals (age range: 18–26 years) with OPF were randomly allocated to the equally sized control and experimental groups. The experimental group performed a sand running exercise protocol for eight weeks. Muscle activities were recorded using an electromyography system. Two variables, including directed co-contraction and general co-contraction, were calculated before and after training programs. Results: In the experimental group, lower directed vastus lateralis/vastus medialis co-contraction, greater general knee co-contraction, and directed medial/lateral knee co-contraction during the mid-stance and push-off phases were found at the post-test compared to the pre-test (P

Excessive muscle co-contraction is one of the factors related to the progression of knee osteoarthritis (OA). A previous study demonstrated that pain, joint instability, lateral thrust, weight, and lower extremity alignment were listed as factors affecting excessive co-contraction in knee OA. However, this study aimed to assess the association between fear-avoidance beliefs and muscle co-contraction during gait and stair climbing in people with knee OA. Twenty-four participants with knee OA participated in this cross-sectional study. Co-contraction ratios (CCRs) were used to calculate muscle co-contraction during walking and stair climbing, using surface electromyography. Fear-avoidance beliefs were assessed by the Tampa Scale for Kinesiophobia-11 (TSK-11) for kinesiophobia and the Pain Catastrophizing Scale (PCS) for pain catastrophizing. Secondary parameters that may influence co-contraction, such as degree of pain, lateral thrust, weight, and lower extremity alignment, were measured. The relationships between the CCR during each movement, TSK-11, and PSC were evaluated using Spearman’s rank correlation coefficient and partial correlation analysis, adjusted by weight and lower extremity alignment. Partial correlation analysis showed a significant correlation only between medial muscles CCR and TSK-11 during stair descent (r = 0.54, p < 0.05). Our study revealed that kinesiophobia could be associated with co-contraction during stair descent in people with knee OA.

Co-contraction training has been proposed to improve muscle strength in the absence of external equipment, yet it is needed to elucidate the effects of co-contraction training and its applicability. Thus, we synthesized the effects of co-contraction training on elbow muscle strength, myoelectric activity, and muscle thickness. We searched papers from MEDLINE via PubMed, Web of Science, Scopus and Embase databases. The inclusion criteria were studies comprising adults between 18-64 years old; investigating chronic effects of co-contraction training on elbow muscles; comparing pre- and post-intervention or control values; presenting any of the outcomes; randomized, quasi-experimental, pre- and post-design; in English. Seven studies met the inclusion criteria. We performed a systematic review and meta-analysis following PRISMA recommendations. We used the revised RoB 2, ROBINS-I to verify the level of evidence. We also included a questionnaire for biomechanical studies and GRADE analysis. We extracted data independently by two investigators, considering the characteristics of study, participants and training, outcomes, and results. We calculated the effect sizes for each outcome. The analysis was carried out by combining and dividing flexors and extensors in a subgroup analysis. Comparing the experimental vs. control group, our results showed that cocontraction training increased isometric strength (SMD=0.51 [0.19, 0.83]) and agonist myoelectric activity (SMD=0.54 [0.25, 0.83]). Comparing pre- vs. post-training, co-contraction training also improved isometric strength (SMD=1.28 [0.75, 1.81]); concentric elbow extensor strength (SMD=0.64 [0.01, 1.26]); and myoelectric activity (SMD=0.46 [0.18, 0.73]). No effect was observed for muscle thickness. The co-contraction training improves muscle performance without morphological changes.

Running is one of the most popular physical activities in the world and is usually done on different surfaces. Different levels of running are associated with overuse injuries. Therefore, this study aimed to evaluate the effect of eight weeks of training on artificial grass, natural grass, and synthetic surface on ankle joint co-contraction during running in individuals with over-pronation. This study was designed as a double-blinded randomized controlled trial. Sixty participants aged 18-30 years with diagnosed excessive pronation of foot were randomly allocated into three intervention groups (natural grass, artificial grass, and synthetic surface) and a control group. Electromyography data during pre and posttest was collected using surface electromyography system. Results did not demonstrated and statistically significant between group differences in in directed and general ankle joint co-contraction (P>0.05). The results of the present study showed that the ankle joint co-contraction during training on three types of artificial grass, natural grass, and synthetic surfaces was not statistically different in individuals with over-pronation. [ABSTRACT FROM AUTHOR]

The aim of the present investigation was twofold. (1) to assess test–retest reliability of normalized mutual information (NMI) values extracted from the surface electromyography (sEMG) signal of muscles pairs of the upper body during dynamic bench press at a high load, and (2) to assess changes in NMI values from before to after a five‐week quasi‐randomized controlled bench press training intervention. For test–retest reliability, 20 strength trained males (age 25 ± 2 years, height 1.81 ± 0.07 m) performed two three‐repetition maximum (3RM) tests in bench press, while sEMG was recorded from six upper body muscles. Tests were separated by 8.2 ± 2.9 days. For the training intervention, 17 male participants (age 26 ± 5 years, height 1.80 ± 0.07 m) trained bench press specific strength training for 5 weeks (TRA), while 13 male participants (age 23 ± 3 years, height 1.80 ± 0.08 m) constituted a control group (CON). 3RM bench press test and sEMG recordings were carried out before and after the intervention period. The NMI values ranged from poor to almost perfect reliability, with the majority displaying substantial reliability. TRA displayed a significant decrease in NMI values during the concentric phase for two agonist–agonist muscle pairs, while one agonist–agonist and two agonist–antagonist muscle pairs increased the NMI values during the eccentric phase. The observed changes did not exceed the minimal detectable threshold, and we therefore cannot surely ascertain that the changes observed in NMI values reflect genuine neural adaptations. [ABSTRACT FROM AUTHOR]

Purpose: Over-pronated foot (OPF) is a common abnormality of the foot. Sand can change lower limb muscle activities. Therefore, the aim of this study was to evaluate the effect of a sand exercise program on knee muscle co-contraction in runners with OPF. Methods: Thirty individuals (age range: 18-26 years) with OPF were randomly allocated to the equally sized control and experimental groups. The experimental group performed a sand running exercise protocol for eight weeks. Muscle activities were recorded using an electromyography system. Two variables, including directed co-contraction and general co-contraction, were calculated before and after training programs. Results: In the experimental group, lower directed vastus lateralis/vastus medialis co-contraction, greater general knee co-contraction, and directed medial/lateral knee co-contraction during the mid-stance and push-off phases were found at the post-test compared to the pre-test (P<0.017). Irrespective of the time, greater directed medial/lateral knee co-contraction during the push-off phase was observed in the experimental group (P=0.043). Conclusion: Sand can be used as a suitable surface for training, as increased muscle co-activation is required to make postural adjustments during running. [ABSTRACT FROM AUTHOR]

The central nervous system uses muscle co-activation for body coordination, effector movement control, and joint stabilization. However, co-activation increases compression and shear stresses on the joints. Lifting activity is one of the leading causes of work-related musculoskeletal problems worldwide, and it has been shown that when the risk level rises, lifting enhances trunk muscle co-activation at the L5/S1 level. This study aims to investigate the co-activation of lower limb muscles during liftings at various risk levels and lifting types (one-person and vs. two-person team lifting), to understand how the central nervous system governs lower limb rigidity during these tasks. The surface electromyographic signal of thirteen healthy volunteers (seven males and six females, age range: 29–48 years) was obtained over the trunk and right lower limb muscles while lifting in the sagittal plane. Then co-activation was computed according to different approaches: global, full leg, flexor, extensor, and rostro-caudal. The statistical analysis revealed a significant increase in the risk level and a decrease in the two-person on the mean and/or maximum of the co-activation in almost all the approaches. Overall, our findings imply that the central nervous system streamlines the motor regulation of lifting by increasing or reducing whole-limb rigidity within a distinct global, extensor, and rostro-caudal co-activation scheme, depending on the risk level/lifting type.

This study aimed to investigate the co-contraction and pre-activation of agonistic and antagonistic muscles in experienced Tai Chi (TC) practitioners during normal walking (NW) and brush-knee twist-step (BKTS). The electromyographic activities of rectus femoris, biceps femoris, and tibialis anterior and lateral gastrocnemius muscles were collected during BKTS and NW in 28 TC practitioners. The pre-activation of knee and ankle joints before initial landing of left foot, and the co-contraction of knee and ankle joint in double-stance phase I (DSI), single-stance phase (SS), double-stance phase II (DSII), and swing phase (SW) were calculated during BKTS and NW. Ankle co-contraction significantly increased during DSI and SS in BKTS movements than compared with that in NW. For DSI and SW, SS and DSII, and DSII and SW, a significant difference was found in BKTS. The pre-activation of knee joint significantly decreased in BKTS and NW. This study indicated greater ankle joint muscle co-contraction in DSI and SS of stance phase and lower knee joint muscle co-contraction and pre-activation than in NW in BKTS movement. In addition, greater ankle joint muscle co-contraction was observed in the DSI, SS, and DSII of stance phase than those of swing phase in BKTS movement. [ABSTRACT FROM AUTHOR]

Purpose: Military boots mileage is a main factor that can affect the risk of running injuries. The present study aims to evaluate the effect of three types of military boots mileage on knee muscular co-contraction during running. Methods: Fifteen healthy males received three pairs of new military boots. Participants wore these boots for more than 6 months. Electromyography activity of lower limb muscles during running at constant speed was recorded during pre- and post-intervention. Then, knee muscular co-contraction was calculated. Results: Results showed a significant increase during loading response (P=0.030, n² p=0.157) and push-off (P=0.008, n² p=0.302) phases for general knee co-contraction at post-test compared to the pre-test. Also, directed mediolateral knee co-contraction showed a significant increment during mid-stance (P=0.028, n² p=0.040) and push-off (P=0.039, n² p=0.115) phases at post-test compared to the pre-test. Conclusion: It can be concluded that knee joint instability while using polyurethane thermoplastic is more than polyurethane boots. Also, our results demonstrated that maintaining knee stability in the anterior-posterior direction while using polyurethane thermoplastic is better than in polyurethane boots. [ABSTRACT FROM AUTHOR]

ObjectiveTo examine the relation of pain sensitization to altered motor activity in knee OA as assessed by hamstrings muscle co-contraction during maximal effort knee extension.DesignMedial, lateral, and overall hamstring co-contraction was assessed in the Multicenter Osteoarthritis (MOST) Study cohort using electromyography during isokinetic knee extension at 60°/second. Mechanical temporal summation of pain (TS) was assessed at the right wrist and pressure pain thresholds (PPT) were assessed at the patellae; PPTs were categorized into sex-specific tertiles. Muscle co-contraction was categorized into age- and sex-specific tertiles. We evaluated the relation of measures of sensitization to muscle co-contraction using a generalized logistic regression model.Results1633 participants were included: mean age and BMI was 67.3 ± 7.7 years and 30.3 ± 5.6 kg/m2, respectively; 58% were female. Presence of TS was associated with higher overall (OR 1.3, 95% confidence interval (CI) (1.0-1.8)), medial (1.4 (1.0-1.9), and lateral (1.3 (1.0, 1.9)) hamstring co-contraction. The lowest PPT tertile (greater sensitivity) was associated with higher overall (1.5 (1.0, 2.3)) and medial (1.5 (1.0, 2.3)) hamstring co-contraction compared with those in the highest PPT tertile.ConclusionGreater pain sensitization, as assessed by presence of TS at the wrist and low patellar PPT, was associated with greater overall and medial hamstring co-contraction during knee extension. This provides support to the possibility that peripheral and/or central nervous system alterations may not only affect pain sensitivity, but also motor function.

Musculoskeletal modelling is used widely for studying limb motion and its control, but simulation outcomes may depend heavily on the underlying muscle model used. The aim of this study was to investigate how intrinsic muscle properties affect reaching movements in a simple upper limb model. The simulations suggest that more realistic, higher-order activation dynamics requires longer prediction from a forward model and gives rise to a higher level of unplanned co-contraction than simple activation models. Consistent with prior work, muscle force-length-velocity properties stabilised and smoothed limb movements and furthermore helped promote accurate reaching performance with the high-order activation model. [ABSTRACT FROM AUTHOR]

Background: The genicular or knee joint angles of terrestrial mammals remain constant during the stance phase of walking; however, the angles differ among taxa. The knee joint angle is known to correlate with taxa and body mass among extant mammals, yet several extinct mammals, such as desmostylians, do not have closely related descendants. Furthermore, fossils lose their soft tissues by the time they are unearthed, making body mass estimates difficult. These factors cause significant problems when reconstructing the proper postures of extinct mammals. Terrestrial mammals use potential and kinetic energy for locomotion; particularly, an inverted pendulum mechanism is used for walking. This mechanism requires maintaining the rod length constant, therefore, terrestrial mammals maintain their joint angle in a small range. A muscle reaction referred to as co-contraction is known to increase joint stiffness; both the agonist and antagonist muscles work simultaneously on the same joint at the same time. The musculus semimembranosus flexes the knee joint and acts as an antagonist to muscles that extend it. Methods: Twenty-one species of terrestrial mammals were examined to identify the elements that constitute the angle between the m. semimembranosus and the tibia based on the period between the hindlimb touching down and taking off from the ground. Measurements were captured from videos in high-speed mode (420 fps), selecting 13 pictures from the first 75% of each video while the animals were walking. The angles between the main force line of the m. semimembranosus and the tibia, which were defined as ϑsm-t, were measured. Results: The maximum and minimum angles between the m. semimembranosus and the tibia (ϑsm-t) of the stance instance (SI) were successfully determined for more than 80% of the target animals (17 out of 21 species) during SI-1 to SI-13 within ±10° from the mean. The difference between each successive SI was small and, therefore, the ϑsm-t transition was smooth. According to the results of the total stance differences among the target animals, ϑsm-t was relatively constant during a stance and, therefore, average ϑsm-t (ϑave) can represent each animal. Only Carnivora had a significant difference in the correlation between body mass and ϑave. In addition, there were significant differences in 0ave between plantigrade and unguligrade locomotion. Conclusion: Our measurements show that ϑave was 100 ± 10° regardless taxon, body mass, and locomotor mode. Thus, only three points on skeletons need to be measured to determine ϑave. This offers a new approximation approach for understanding hindlimb posture that could be applied to the study of the hindlimbs of extinct mammals with no closely related extant descendants. [ABSTRACT FROM AUTHOR]

The naturally occurring variability in our movements often poses a significant challenge when attempting to produce precise and accurate actions, which is readily evident when playing a game of darts. Two differing, yet potentially complementary, control strategies that the sensorimotor system may use to regulate movement variability are impedance control and feedback control. Greater muscular co-contraction leads to greater impedance that acts to stabilize the hand, while visuomotor feedback responses can be used to rapidly correct for unexpected deviations when reaching toward a target. Here, we examined the independent roles and potential interplay of impedance control and visuomotor feedback control when regulating movement variability. Participants were instructed to perform a precise reaching task by moving a cursor through a narrow visual channel. We manipulated cursor feedback by visually amplifying movement variability and/or delaying the visual feedback of the cursor. We found that participants decreased movement variability by increasing muscular co-contraction, aligned with an impedance control strategy. Participants displayed visuomotor feedback responses during the task but, unexpectedly, there was no modulation between conditions. However, we did find a relationship between muscular co-contraction and visuomotor feedback responses, suggesting that participants modulated impedance control relative to feedback control. Taken together, our results highlight that the sensorimotor system modulates muscular co-contraction, relative to visuomotor feedback responses, to regulate movement variability and produce accurate actions. NEW & NOTEWORTHY The sensorimotor system has the constant challenge of dealing with the naturally occurring variability in our movements. Here, we investigated the potential roles of muscular co-contraction and visuomotor feedback responses to regulate movement variability. When we visually amplified movements, we found that the sensorimotor system primarily uses muscular co-contraction to regulate movement variability. Interestingly, we found that muscular co-contraction was modulated relative to inherent visuomotor feedback responses, suggesting an interplay between impedance and feedback control. [ABSTRACT FROM AUTHOR]

Functional knee braces are frequently prescribed by physicians to ameliorate the function of individuals with anterior cruciate ligament (ACL) injuries. These braces have been shown in the literature to potentially enhance knee stability by augmenting muscle activation patterns and the timing of muscle response to perturbations. However, very few techniques are available in the literature to quantify how those modifications in lower-limb muscle activity influence stability of the knee. The aim of the present study was to quantify the effect of an off-the-shelf functional knee brace on muscle contributions to knee joint rotational stiffness in ACL-deficient and ACL-reconstructed patients. Kinematic, electromyography, and kinetic data were incorporated into an electromyography-driven model of the lower extremity to calculate individual and total muscle contributions to knee joint rotational stiffness about the flexion-extension axis, for 4 independent variables: leg condition (contralateral uninjured, unbraced ACL injured, and braced ACL injured); knee flexion (5°-10°, 20°-25°, and 30°-35°); squat stability condition (stable and unstable); and injury status (ACL deficient and ACL reconstructed). Participants had significantly higher (P < .05, η² = .018) total knee joint rotational stiffness values while wearing the brace compared with the control leg. A 2-way interaction effect between stability and knee flexion (P < .05, η² = .040) for total joint rotational stiffness was also found. [ABSTRACT FROM AUTHOR]

Estimation of the force exerted by muscles from their electromyographic (EMG) activity may be useful to control robotic devices. Approximating end-point forces as a linear combination of the activities of multiple muscles acting on a limb may lead to an inaccurate estimation because of the dependency between the EMG signals, i.e., multi-collinearity. This study compared the EMG-to-force mapping estimation performed with standard multiple linear regression and with three other algorithms designed to reduce different sources of the detrimental effects of multi-collinearity: Ridge Regression, which performs an L2 regularization through a penalty term; linear regression with constraints from foreknown anatomical boundaries, derived from a musculoskeletal model; linear regression of a reduced number of muscular degrees of freedom through the identification of muscle synergies. Two datasets, both collected during the exertion of submaximal isometric forces along multiple directions with the upper limb, were exploited. One included data collected across five sessions and the other during the simultaneous exertion of force and generation of different levels of co-contraction. The accuracy and consistency of the EMG-to-force mappings were assessed to determine the strengths and drawbacks of each algorithm. When applied to multiple sessions, Ridge Regression achieved higher accuracy (R2 = 0.70) but estimations based on muscle synergies were more consistent (differences between the pulling vectors of mappings extracted from different sessions: 67%). In contrast, the implementation of anatomical constraints was the best solution, both in terms of consistency (R2 = 0.64) and accuracy (74%), in the case of different co-contraction conditions. These results may be used for the selection of the mapping between EMG and force to be implemented in myoelectrically controlled robotic devices. [ABSTRACT FROM AUTHOR]

When humans are exposed to a predictable external perturbation, they usually generate anticipatory postural adjustments (APAs), which reduce the effect of potential body disturbance. However, when an external perturbation comes from behind and as such unpredicted, no APAs are generated, which challenges postural control. The aim of this study was to examine whether humans exposed to unpredictable perturbations could generate APAs using an auditory cue. Ten young adults were exposed to external perturbations hitting their shoulders from behind with or without an auditory cue prior to the physical impact. Electromyography (EMG) activities of eight trunk and leg muscles and center-of-pressure (COP) displacements were recorded and analyzed during the anticipatory and compensatory phases of postural control. Outcome measures included the latencies and integrals of muscle activities, COP displacements, and indices of co-contraction and reciprocal activation of muscles. The results showed that young adults were able to rely on an auditory cue to generate APAs prior to external perturbations coming from behind, and they demonstrated stronger APAs with training. Moreover, they utilized co-contraction of ventral and dorsal muscles as their APA response. The outcome provides a foundation for future studies aiming at using auditory cues to facilitate the generation of APAs and improve postural control in people with impaired balance while exposed to perturbations. [ABSTRACT FROM AUTHOR]

BACKGROUND: The ability of the lower-extremity muscle activation directly affects the performance and in turn interacts with the loading conditions of the muscle itself. However, systematic information concerning the characteristics of lower-extremity muscle during landings is lacking. In particular, the landing height and shoes are also important factors based on the actual situation, which could further contribute to understanding the neuromuscular activity and how biochemical response of the body tissues to double-leg drop landings. OBJECTIVE: The study was to investigate the effects of landing tasks on the activation of lower-extremity muscles and explore the relationship among movement control, landing heights, shoe cushioning, and muscle activities. METHODS: Twelve male basketball players were recruited to perform drop jump (DJ) and passive landing (PL) from three heights (30, 45, and 60 cm) while wearing highly-cushioned basketball shoes (HC) and less-cushioned control shoes (LC). EMG electrodes were used to record the activities of the target muscles (rectus femoris, vastus lateralis, biceps femoris, tibialis anterior, and lateral gastrocnemius) during the landing tasks. RESULTS: Pre- and post-activation activity of the lower-extremity muscles significantly decreased during PL compared with those during DJ (p < 0.05). No significant shoe effects on the characteristics of muscle activation and coactivation during DJ movements were observed. However, the participants wearing LC showed significantly higher muscle post-activation (p < 0.05) at the three drop heights during PL compared with those wearing HC. Coactivation of the ankle muscles was higher in LC than in HC during 30-cm PL (p < 0.05). CONCLUSIONS: The activation patterns of lower-extremity muscles can be significantly influenced by landing types. Highlycushioned basketball shoes would help reduce the risk of injuries by appropriately tuning the muscles during the PL. [ABSTRACT FROM AUTHOR]

Muscle co-contraction can result in higher joint contact forces, compromising knee joint mobility for stability, thus leading to impaired lower extremity neuromuscular control, delayed return to sports, and increased incidence of secondary anterior cruciate ligament (ACL) injury post-ACL reconstruction. Hybrid assistive limb (HAL) training has the potential to correct impairment of antagonistic or synergistic muscle movement of the knee joint through bioelectric signal feedback from muscle signals with computer processing. We considered that HAL training would contribute to improve peak muscle torque through coordinating or decreasing higher levels of muscle co-contractions and reducing differences between hamstring and quadriceps muscle activity on electromyography (EMG). While playing handball, a 20-year-old female injured her ACL upon landing on one leg. Two months post-injury, she underwent arthroscopic, anatomic single-bundle ACL reconstruction with a semitendinosus tendon autograft. At a 4-month follow-up, she underwent knee HAL training, which was performed once a week for three sessions. EMG data were collected during the evaluations of pre- and post-HAL training. The average muscle amplitude was used to calculate the difference between vastus lateralis (VL) and semitendinosus (ST) muscles, and the muscle co-contraction index (CCI). The CCI reflects the simultaneous activation of antagonistic muscles, which is determined for knee extensor-flexor muscle pairs. Post-knee HAL training, the CCI of the lateral hamstring and quadriceps muscles during extension was lower than that during pre-HAL training in all sessions. However, no differences were found in the CCI for the medial hamstring and quadriceps muscles during extension and flexion pre- and post-knee HAL training. For post-knee HAL training, the difference between VL and ST EMG data during a closed-chain squat was lower than that during pre-HAL training in all sessions. Knee HAL training contributed to improved peak muscle torque through coordinating or decreasing higher levels of muscle co-contractions, and it reduced differences between hamstring and quadriceps muscle activity in the ACL reconstructed leg as depicted by EMG.

Purpose: Military boots mileage is a main factor that can affect the risk of running injuries. The present study aims to evaluate the effect of three types of military boots mileage on knee muscular co-contraction during running. Methods: Fifteen healthy males received three pairs of new military boots. Participants wore these boots for more than 6 months. Electromyography activity of lower limb muscles during running at constant speed was recorded during pre- and post-intervention. Then, knee muscular co-contraction was calculated. Results: Results showed a significant increase during loading response (P=0.030, n2p=0.157) and push-off (P=0.008, n2p=0.302) phases for general knee co-contraction at post-test compared to the pre-test. Also, directed mediolateral knee co-contraction showed a significant increment during mid-stance (P=0.028, n2p=0.040) and push-off (P=0.039, n2p=0.115) phases at post-test compared to the pre-test. Conclusion: It can be concluded that knee joint instability while using polyurethane thermoplastic is more than polyurethane boots. Also, our results demonstrated that maintaining knee stability in the anterior-posterior direction while using polyurethane thermoplastic is better than in polyurethane boots.

Purpose: The purpose of this study was to compare the effects of two different approaches of dual-task training and executive training on lower limb muscular activity in older adults with balance impairment. Methods: This was a quasi-experimental study performed with a pre-test and post-test method. Thirty old adults (Mean±SD age=73.8±4.6 y, height=1.65±0.06 m, weight=69.17±12.67 kg) were randomly assigned to one of the three groups: two experimental groups included Cognitive Dual-Task training (CDT; participants did exercises under the dual-task condition with cognitive tasks, such as forward counting, simple visual search task, etc.) and Executive Function training (EF; included a mixture of 20 tasks involving working memory tasks, inhibitory and speed of processing tasks), and a control group. The training session lasted 45 min and was held three times a week for eight weeks. Gait muscle activity under single-task and Dual-Task (DT) conditions was recorded before and after training. Results: during the stance phase of normal walking, the amplitude of Electromyography (EMG) activity of right Tibialis Anterior (TA) muscle in the post-test was about 32% lower than that in the pre-test in the CDT group (P=0.011), and no statistically significant change was between pre- and post-training in the EF and control groups (P>0.05). During the swing phase of DT walking, the amplitude of EMG activity of the right Vastus Lateralis (VL) muscle in the post-test was about 15.5% higher than that in the pre-test in the CDT group (P=0.013), and in the right VL muscle during the post-test was lower than that in the pre-test in the EF group (P=0.01). In the CDT group, right ankle co-contraction during the stance phase in the post-test was statistically different from that in the pre-test. In all three groups, muscular EMG asymmetry demonstrated no statistically significant change between pre- and post-training measures (P>0.05). Conclusion: Overall, both training groups showed similar muscular activity in the post-test than pre-test; however, in the EF training group, walking velocity improved more than that in the CDT group. Therefore, because of improvements in both walking velocity and muscle activities after EF training, this training mode is suggested for older adults.

Walking after stroke is often described as requiring excessive muscle co-contraction, yet, evidence that co-contraction is a ubiquitous motor control strategy for this population remains inconclusive. Co-contraction, the simultaneous activation of agonist and antagonist muscles, can be assessed with electromyography (EMG) but is often described qualitatively. Here, our goal is to determine if co-contraction is associated with gait impairments following stroke. Fifteen individuals with chronic stroke and nine healthy controls walked on an instrumented treadmill at self-selected speed. Surface EMGs were collected from the medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA) of each leg. EMG envelope amplitudes were assessed in three ways: (1) no normalization, (2) normalization to the maximum value across the gait cycle, or (3) normalization to maximal M-wave. Three co-contraction indices were calculated across each agonist/antagonist muscle pair (MG/TA and SOL/TA) to assess the effect of using various metrics to quantify co-contraction. Two factor ANOVAs were used to compare effects of group and normalization for each metric. Co-contraction during the terminal stance (TSt) phase of gait is not different between healthy controls and the paretic leg of individuals post-stroke, regardless of the metric used to quantify co-contraction. Interestingly, co-contraction was similar between M-max and non-normalized EMG; however, normalization does not impact the ability to resolve group differences. While a modest correlation is revealed between the amount of TSt co-contraction and walking speed, the relationship is not sufficiently strong to motivate further exploration of a causal link between co-contraction and walking function after stroke. Co-contraction does not appear to be a common strategy employed by individuals after stroke. We recommend exploration of alternative EMG analysis approaches in an effort to learn more about the causal mechanisms of gait impairment following stroke.

Background: Foot pronation is in the open kinetic chain composed of eversion, abduction, and ankle dorsiflexion. Foot overpronation may be associated with different lower limb injuries. The purpose of this study was to investigate the effect of walking on the sand on co-Contraction of the lower limb muscles in individuals with overpronated foot. Methods: The present study was a semi-experimental and laboratory type. Thirty healthy individuals and 30 individuals with foot overpronation volunteered to participate in this study. Muscle activity was recorded by an 8-channel electromyography system with a surface electrode during walking on sand. Two-way ANOVA test was used for statistical analysis at the significant level P0/05). Conclusion: Individuals with overpronated foot demonstrated lower ankle-directed co-Contraction during walking on sand compared with walking on stable level ground. Individuals with overpronated foot showed a greater ankle-directed co-Contraction than the healthy group. Decreased ankle-directed co-Contraction indicated a positive effect of walking on sand in individuals with foot overpronation.

The frequency of obstetric palsy ranges from 0.5 to 3.0 cases per 1000 live births. The functional outcome disorders are determined by the nature of the damage and the number of damaged roots of the brachial plexus. There are 50 % of patients have complete recovery, 15 % have severe functional disorders of the upper limb, and 35 % have some limitation of the shoulder joint function. There are 3 variants of residual phenomena in children with obstetric palsy: paresis, paralysis, and co‑contraction. The article describes the mechanisms of nerve regeneration in children and adults, the pathogenesis of contractions and motor disorders in general in children with obstetric palsy, and modern methods of treatment of co‑contraction. This article will be useful for neurologists, rehabilitation specialists, and orthopedists.

Background: A lot of authors have been studied the consequence of postural control strategies through investigating the effects of foot-surface contact. In this context an important variable of textured surfaces or insoles could be related to material stiffness. We apply a particular textured insoles to evaluate neuromuscular response of plantar stimulation during walking.Research Question: Could textured insoles alter the human locomotion during walking at different speeds?Methods: Ten adults (age: 27 ± 5 years) completed three trials on the multifunction treadmill at 0.42 ms-1, 0.89 ms-1, and 1.5 ms-1 walking speed. Temporal-spatial parameters, gait line, and kinetic parameters were analyzed. The Co-Contraction Index (CCI) and electromyography (EMG) of the right leg muscles were assessed during four phases of gait: first half stance (FHS), half stance (HS), second half stance (SHS), swing phase (SP). Textured insole and soft control insole were worn while walking.Results: Plantar stimulation improved cadence, stride time, stride length and gait line parameters with increasing speed. First force peaks and maximum force forefoot were always significant. The maximum force midfoot was significant at 0.42 and 0.89 ms-1. The maximum force heel only was significant in lower velocity. The maximum pressure showed different significant values except for the heel. Significant differences in the CCI were always found in the FHS and SHS for the plantar muscles, and in the FHS and HS for the knee muscles. The differences in gait analysis in biomechanical and in electromyographic parameters were more significant in the higher speed tested.Significance: The perception of shape and texture through its linear response to skin deformation over a wide range of deformations could be the reason why the significant differences increase in the higher speed. In conclusion, sensory interventions fallowing appropriate insoles can influence significantly gait. Walking strategy positively adjusts locomotion with high efficiency. [ABSTRACT FROM AUTHOR]

BackgroundThe aim of osteomyoplastic transfemoral amputation (OTFA) is to produce sustained, robust prosthetic gait performance by residuum reconstructing. A better understanding of residuum-socket interface pressures (RSI) and residuum muscle activation should uniquely reveal gait stability to better inform long-term rehabilitation goals.ObjectivesThe objectives of this study are to characterize RSI pressures and residuum muscle activation in men with OTFA while walking at two speeds and compare temporospatial muscle activation with intact controls.MethodsIn this study, we observed and compared healthy men with OTFA and controls during 2-min gait trials at brisk and self-paced speeds, two visits, and 1 year apart. RSI pressures and hip adductors, hamstrings, and quadriceps activation were recorded for those with OTFA. OTFA temporospatial muscle activation patterns were compared with the controls. Within the extracted strides, heel-strike and toe-off events and EMG activation peak times were characterized and compared. Peak times for pressure and EMG activity were examined in individual muscles and antagonist muscles of residual and intact limbs.ResultsSix men with OTFA exhibited adductor, hamstring, and quadriceps co-contraction within intact and residual limbs, regardless of walking speed or trial. Co-contraction within their intact limb occurred throughout the gait cycle. Within the residuum, co-contraction occurred during weight transference. The 75% most likely RSI peaks occurred during stance. EMG peaks were 75% most likely to occur during early stance, terminal stance-initial swing, and terminal swing.ConclusionParticipants with OTFA demonstrated adductors-hamstrings-quadriceps co-contraction in the intact thigh and residuum with corresponding RSI pressure increase, primarily during transitions between stance and swing, indicating gait instability, demonstrating the need to explicitly address these deficits continuously in rehabilitation and wellness settings.

Background: Declines in muscular function may hinder our ability to properly respond balance perturbations during walking. Examining age-related differences in muscle activation during balance-perturbed walking could be an important summary of literature to guide future clinical or scientific research.Research Question: Are there differences in lower limb muscle activation between young and older adults when responding to balance perturbations during walking?Methods: A literature search was conducted in October 2020 to identify relevant articles using Pubmed, Scopus, Web of Science, Ovid EMBASE, and CINAHL. Inclusion criteria were defined to identify studies investigating lower limb muscle activation in healthy older adults during balance-perturbed walking. Data extraction was independently performed by both authors. Outcome measures included key findings of lower limb muscle activations during walking and balance-related tasks (e.g. multidirectional perturbations, different speeds, cognitive tasks, slippery/slopes, and obstacles).Results: This article reviewed fourteen studies including 230 older adults (age: 70 ± 4.5, females: 124 [53.9%]) and 230 young adults (age: 23 ± 2.0, females: 113 [49.1%]). The overall quality of included studies was fair, with a mean score of 76%. Twelve lower limb muscles were assessed during balance-perturbed walking. All studies reported electromyographic measurements, including magnitude, timing, co-contraction indices, and variability of activation.Significance: Compared to young adults, older adults demonstrated different adaptations in lower limb muscle activation during balance-perturbed walking. Co-contraction of ankle and knee joint muscles had more conclusive results, with the majority reporting an increased co-contraction in older adults, especially when balance is perturbed by a physical task. These data suggest that coordination between agonist and antagonist muscles is important to provide necessary stabilization during balance-perturbed walking. [ABSTRACT FROM AUTHOR]

Objective: Ankle joint stiffness is known to be modulated by co-contraction of the ankle muscles; however, it is unclear to what extent changes in agonist muscle activation alone affect ankle joint stiffness. This study tested the effects of varying levels of ankle muscle activation on ankle joint mechanical stiffness in standing and during the late stance phase of walking. Methods: Dorsiflexion perturbations were applied at various levels of ankle muscle activation via a robotic platform in standing and walking conditions. In standing, muscle activation was modulated by having participants perform an EMG target matching task that required varying levels of plantarflexor activation. In walking, muscle activation was modulated by changing walking speeds through metronome-based auditory feedback. Ankle stiffness was evaluated by performing a Least-squares system identification using a parametric model consisting of stiffness, damping, and inertia. The association between ankle muscle activation and joint stiffness was evaluated using correlation analyses. Linear regression models were used to determine the extent to which muscle activation contributed to ankle stiffness. An inclusive statistical approach (both classical and Bayesian analyses) was adopted to measure the statistical significance (p-value) and Bayes Factor (BF10). Results: Results indicate that plantarflexor activity was positively correlated with ankle stiffness in both standing and walking (p<0.001, BF10900), whereas dorsiflexor activity was negatively correlated with ankle stiffness in walking (p = 0.014, BF10 = 3.9) but not in standing (p = 0.725). Regression analyses indicated that ankle muscle activation predicted about 84% of the variation in ankle stiffness in standing and 45% in walking (p<0.001, BF10100). Conclusion: Ankle muscle activation significantly contributes to ankle stiffness during standing and walking. Significance: The results highlight the role of muscle activation on maintaining joint stiffness and underscore the importance of accounting for muscle activation when measuring ankle stiffness in healthy as well as patient populations. [ABSTRACT FROM AUTHOR]

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Background: The net metabolic cost of walking (NCw) and the co-activation of leg muscles are both higher in old adults (OG) than in young adults (YG). Nevertheless, the relation between the two remains unresolved, mainly due to the controversial co-activation measurement method used in previous studies.Research Question: To compare ankle and knee co-contraction (CCI), calculated using an EMG-driven method, between the groups and to examine their relationship with NCw.Methods: Nine young (YG = 25.2 +/- 3.3 years old) and nine older (OG = 68.7 +/5.9 years old) adults walked on a treadmill at five speeds (YG: 1; 1.2; 1.4; 1.6; 1.8 m/s; OG: 0.6; 0.8; 1; 1.2; 1.4 m/s) while electromyography (sEMG) and oxygen consumption were measured. CCI were calculated around the ankle and knee for different parts of the gait cycle (entire gait cycle 0-100 %, stance phase 0-60 %, swing phase 60-100 %).Results: NCw was significantly higher (25 %, averaged over the walking speeds) in OG as were Knee_CCI, Knee_CCI_swing and Knee_CCI_stance. Multiple regression models in YG, OG and YG + OG highlighted Ankle_CCI as the main contributor in NCw (β = 0.08-0.188, p < 0.05) with a positive relation between the two variables.Significance: The present findings provide a better understanding of the association between muscle co-contraction and metabolic cost in older adults. It may help scientists and clinicians to further develop strategies aimed at neuromuscular rehabilitation as a means of improving mobility and independence among older adults. [ABSTRACT FROM AUTHOR]

The incidence of plexus brachial birth injuries consists 0.12 % of births (0.04–0.20 %). Although the possibility of complete recovery is relatively high, 10–30 % patients have secondary deformity and limitation of upper limb function due to muscle imbalance and co-contraction around the shoulder and elbow cause abnormal motor performance, osseous deformities and joint contracture. Botulinum toxin type A injections into targeted muscles in combination with occupation therapy, physiotherapy or operative treatment reduce the abnormal cocontraction of the antagonist muscles and help to restore muscles balance and prevent secondary deformities. The article discuses indications for botulinum injection therapy, target muscles, doses of botulinum toxin A, optimal patient’s age and results of treatment.

Introduction: Malalignments in the lower limb can affect the biomechanics of human movements such as walking. The ankle joint has a major role in shock absorption, however abnormalities such as genu valgum can disrupt its function. The objective in this study is to investigate the effect of corrective exercise with ThraBand® on the ankle joint co-contraction in patients with genu valgum during walking. Materials and Methods: 24 male students (20-30 years old) were randomly divided into the two control and experimental groups. Corrective exercises were performed for 8 weeks using TheraBand® for the experimental group. The electrical activity of the selected muscles was recorded by the electromyography (ECG) device (Biometrics Ltd, UK). The statistical analysis was performed using the SPSS software and repeated measures analysis of variance (ANOVA) at the significant level of 0.050. Results: Findings in the experimental group showed that the general co-contraction of ankle joint increased significantly in the heel contact phase during the post-test phase compared to the pre-test phase (P = 0.044; d = 0.12). Other components did not show any significant differences (P > 0.050). Conclusion: Generally, increased co-contraction of ankle during the heel contact phase indicated greater ankle joint support after the corrective exercise.

Objective. Non-invasive, high-density electromyography (HD-EMG) has emerged as a useful tool to collect a range of neurophysiological motor information. Recent studies have demonstrated changes in EMG features that occur after stroke, which correlate with functional ability, highlighting their potential use as biomarkers. However, previous studies have largely explored these EMG features in isolation with individual electrodes to assess gross movements, limiting their potential clinical utility. This study aims to predict hand function of stroke survivors by combining interpretable features extracted from a wearable HD-EMG forearm sleeve. Approach. Here, able-bodied ( N = 7) and chronic stroke subjects ( N = 7) performed 12 functional hand and wrist movements while HD-EMG was recorded using a wearable sleeve. A variety of HD-EMG features, or views, were decomposed to assess alterations in motor coordination. Main Results. Stroke subjects, on average, had higher co-contraction and reduced muscle coupling when attempting to open their hand and actuate their thumb. Additionally, muscle synergies decomposed in the stroke population were relatively preserved, with a large spatial overlap in composition of matched synergies. Alterations in synergy composition demonstrated reduced coupling between digit extensors and muscles that actuate the thumb, as well as an increase in flexor activity in the stroke group. Average synergy activations during movements revealed differences in coordination, highlighting overactivation of antagonist muscles and compensatory strategies. When combining co-contraction and muscle synergy features, the first principal component was strongly correlated with upper-extremity Fugl Meyer hand sub-score of stroke participants ( R 2 = 0.86). Principal component embeddings of individual features revealed interpretable measures of motor coordination and muscle coupling alterations. Significance. These results demonstrate the feasibility of predicting motor function through features decomposed from a wearable HD-EMG sleeve, which could be leveraged to improve stroke research and clinical care., (Creative Commons Attribution license.)

Trunk motion is most likely to influence knee joint injury risk, but little is known about sex-related differences in trunk neuromuscular control during changes of direction. The purpose of the present study was to test whether differences in trunk control between males and females during changes of direction exist. Twelve female and 12 male recreational athletes (with at least 10 years of experience in team sport) performed unanticipated changes of direction with 30° and 60° cut angles, while 3D trunk and leg kinematics, ground reaction forces and trunk muscles electromyography were recorded. Trunk kinematics at the time of peak knee abduction moment and directed co-contraction ratios for trunk muscles during the pre-activation and weight acceptance phases were determined. None of the trunk kinematics and cocontraction ratio variables, nor peak knee abduction moment differed between sexes. Compared to the 30° cut, trunk lateral flexion remained unchanged and trunk external rotation was reduced (p < 0.001; η²p (partial eta squared for effect size) = 0.78), while peak knee abduction moment was increased (p < 0.001; η²p = 0.84) at 60°. The sharper cutting angle induced muscle co-contraction during the pre-activation directed less towards trunk flexors (p < 0.01; η²p = 0.27) but more towards trunk medial flexors and rotators opposite to the movement direction (p < 0.001; η²p > 0.46). However, muscle co-contraction during the weight acceptance phase remained comparable between 30° and 60°. The lack of sex-related differences in trunk control does not explain knee joint injury risk discrepancies between sexes during changes of direction. Trunk neuromuscular strategies during sharper cutting angles revealed the importance of external oblique muscles to maintain trunk lateral flexion at the expense of trunk rotation. This provides new information for trunk strength training purposes for athletes performing changes of direction. [ABSTRACT FROM AUTHOR]

Sex, head and neck posture, and cervical muscle preparation are contributing factors in the severity of head and neck injuries. However, it is unknown how these factors modulate the head kinematics. In this study, twenty-four (16 male and 8 female) participants experienced 50 impulsive forces to their heads with and without an acoustic warning. Female participants demonstrated a 71 ms faster (p = 0.002) muscle activation onset compared to males after warning. The magnitude of muscle activation was not significant between sexes. Females exhibited 21% (p < 0.008) greater peak angular velocity in all force directions and 18% (p < 0.04) greater peak angular acceleration in sagittal plane compared to males. Females exhibited 15% (p = 0.03) greater peak linear acceleration compared to males only in sagittal flexion. Preparation attenuated head kinematics significantly (p < 0.03) in 11 out of 18 investigated head kinematics for both sexes. A warning eliciting a startle response 420 ms prior to the impact resulted in significant attenuation of all measured head kinematics in sagittal extension (p < 0.037). In conclusion, both sex and warning type were significant factors in head kinematics. These data provide insight into the complex relationship of muscle activation and sex, and may help identify innovative strategies to reduce head and neck injury risk in sports. [ABSTRACT FROM AUTHOR]

The aim of this study was to characterise wrist extensor and flexor muscle activity during combinations of moderate-to-high handgrip and wrist forces that are similar to actions and intensities used in many workplace settings. Surface electromyography was recorded from three wrist flexors and three wrist extensors while participants performed simultaneous handgrip forces and wrist forces ranging in intensities from 15% to 60% of maximum. While the wrist flexors were highly task-dependent, in that their activity significantly changed between conditions, wrist extensor activity was consistently high throughout the experiment. Wrist joint co-contraction was also significantly higher when the wrist extensors were functioning as the antagonists. These findings suggest that the wrist extensors likely demonstrate consistently higher muscleactivity during most tasks of the hand and wrist, which is likely a leading mechanism behind why they develop chronic overuse injuries more frequently than the wrist flexors. Practitioner Summary: This study was conducted to identify forearm muscle activity patterns that might help explain why the wrist extensors develop overuse injuries more frequently than the flexors. Results demonstrated that the wrist extensors are consistently, highly active during combined handgrip and wrist forces and exhibit no periods of low muscle activity. Abbreviations: BB: biceps brachii; ECR: extensor carpi radialis; ECU: extensor carpi ulnaris; ED: extensor digitorum; EMG: electromyography; ES: effect size; FCR: flexor carpi radialis; FCU: flexor carpi ulnaris; FDS: flexor digitorum superficialis; MVC: maximal voluntary contraction; MVE: maximal voluntary excitation; SD: standard deviation; SE: standard error; TB: triceps brachii [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to compare the effects of two different approaches of dual-task training and executive training on lower limb muscular activity in older adults with balance impairment. Methods: This was a quasi-experimental study performed with a pre-test and post-test method. Thirty old adults (Mean±SD age=73.8±4.6 y, height=1.65±0.06 m, weight=69.17±12.67 kg) were randomly assigned to one of the three groups: two experimental groups included Cognitive Dual-Task training (CDT; participants did exercises under the dual-task condition with cognitive tasks, such as forward counting, simple visual search task, etc.) and Executive Function training (EF; included a mixture of 20 tasks involving working memory tasks, inhibitory and speed of processing tasks), and a control group. The training session lasted 45 min and was held three times a week for eight weeks. Gait muscle activity under single-task and Dual-Task (DT) conditions was recorded before and after training. Results: during the stance phase of normal walking, the amplitude of Electromyography (EMG) activity of right Tibialis Anterior (TA) muscle in the post-test was about 32% lower than that in the pre-test in the CDT group (P=0.011), and no statistically significant change was between pre- and post-training in the EF and control groups (P>0.05). During the swing phase of DT walking, the amplitude of EMG activity of the right Vastus Lateralis (VL) muscle in the post-test was about 15.5% higher than that in the pre-test in the CDT group (P=0.013), and in the right VL muscle during the post-test was lower than that in the pre-test in the EF group (P=0.01). In the CDT group, right ankle co-contraction during the stance phase in the post-test was statistically different from that in the pre-test. In all three groups, muscular EMG asymmetry demonstrated no statistically significant change between pre- and post-training measures (P>0.05). Conclusion: Overall, both training groups showed similar muscular activity in the post-test than pre-test; however, in the EF training group, walking velocity improved more than that in the CDT group. Therefore, because of improvements in both walking velocity and muscle activities after EF training, this training mode is suggested for older adults. [ABSTRACT FROM AUTHOR]