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Background: Shoe mileage may influence the risk of sustaining injuries during walking.Research Question: What are the effects of shoe mileage on knee and ankle muscle co-contraction during walking in females with genu varus?Methods: Fifteen healthy and 15 women diagnosed with genu varus received a new pair of running shoes. They were asked to wear these shoes over 6 months. Pre and post intervention, muscle activities of the dominant limb were recorded during a walking test at preferred gait speed. Two dependent variables were assessed to examine muscle co-contraction: (1) directed co-contraction ratios of agonists and antagonists, and (2) general joint muscle co-contraction.Findings: Results demonstrated significant main effects of the "shoe" factor for general ankle co-contraction during the push-off phase (p = 0.013, d = 1.503). Irrespective of experimental group, paired comparisons revealed significantly lower general ankle co-contraction during the push-off phase after the intervention. A significant main effects of "shoe" for general knee co-contraction during loading phase (p = 0.025, d = 0.895) was also observed. In both groups, paired comparison revealed significantly lower general knee co-contraction during the push-off phase in the post condition. We did not find any significant main effect of group nor group-by-shoe interaction for general ankle co-contraction during the stance phase. Likewise, we did not observe any significant main effect of "shoe", "group" and "group-by-shoe" interaction for mediolateral directed knee co-contraction during stance phase of walking (p > 0.05).Significance: Our findings showed that the shoe mileage but not the genu varus condition affects the general and directed co-contraction of the muscles stabilizing the knee and ankle joints. Together with the observed findings on ankle and knee muscle co-contraction, it is essential to change running shoes after a long wearing time in both healthy and genu varus females. [ABSTRACT FROM AUTHOR]

The spectral properties of surface electromyographic (EMG) signal in the rectus femoris (RF) and the coactivation in the medial hamstrings (MH) were investigated in 45 stroke subjects (22 ± 12 days post-onset) and 30 age-matched healthy controls who performed unilateral knee extensions at maximum effort (100% MVC) and during 5-s force-matching tasks (10, 30, 50% MVC). The spectral properties were obtained through a power spectrum analysis based on Fast Fourier Transform. The coactivation was measured as the MH amplitude (%max) and MH/RF amplitude ratio. Force variability was expressed as the coefficient of variation. Both knee extensors and flexors were weaker in the paretic leg than the non-paretic and control legs (p < 0.001). A significantly higher relative power in the 5–13 and 13–30 Hz bands was found in the paretic than the non-paretic leg across all force levels (p ≤ 0.001) without changes in the 30–60 and 60–100 Hz bands or the mean and median frequencies. Regarding the antagonist coactivation, MH amplitude in the paretic leg was higher than in the non-paretic leg (submaximal levels, p < 0.0001) and the control leg (all force levels, p = 0.0005) with no differences between legs in the MH/RF ratio. The steadiness of the knee extension force was not related to the spectral properties of the agonist EMG or antagonistic coactivation. Greater coactivation was associated with weaker paretic knee flexors (p ≤ 0.0002). The overall results suggest variably altered agonist activation and antagonistic coactivation over the range of isometric knee extension contractions in subacute stroke. [ABSTRACT FROM AUTHOR]

Patient experience of motor recovery from denervation paralysis is complex and textured. The Medical Research Council (MRC) system of grading muscle peak volitional force is widely used as a single measure of assessment. However, it is becoming clear that current motor function assessments are not reflecting the patient lived experience of muscle reinnervation. Therefore, this study aimed to engage international expert nerve surgeons in a classical Delphi process to achieve a consensus of opinion on the ideal clinical assessment of motor function. This was compared with patient-reported impairments of reinnervated muscle. Invitations to engage in the Delphi process were extended to expert peripheral nerve surgeons across two international specialist meetings. For comparison, patients who attended a "Nerve Injury Community Day" were invited to complete a questionnaire on patient-reported impairments of reinnervated muscle. Questions were designed on the basis of a literature review and the clinical experiences of a specialist nerve injury unit. A combination of direct yes/no, multiple choice, open-ended and Likert questions were employed throughout the questionnaires. Eighteen surgeons engaged with the Delphi process; 18 and 11 responded to the first and second rounds respectively. Thirty-one patients responded to the questionnaire. It was found that clinicians were strongly biased towards efferent assessments of muscular function, while patients strongly favoured muscular fatigue, co-contraction and pain when monitoring their own recovery. The findings suggest that current clinical assessments of muscular function are inadequate and should embody measurements of afferent muscular function to better reflect the lived experience of muscle reinnervation. [ABSTRACT FROM AUTHOR]

Introduction Chemotherapy-induced peripheral neuropathy (CIPN) may cause functional impairments such as gait or balance disorders, that increase fall risk. Gait disorders may be due to the neurotoxic effect of chemotherapy that causes a prolonged H-reflex latency and inability to inhibit spinal excitability (H-reflex), resulting in increased co-contraction of the lower extremity muscles. Purpose To assess the efficacy of a home-based exercise program on lower extremity muscle co- contraction, spatio-temporal gait factors, and fall risk in a multiple myeloma cancer patient undergoing chemotherapy and experiencing CIPN. Methods A case study was performed on a 67-year-old male diagnosed with multiple myeloma without achieving remission. The participant initially received 5 months of Velcade (bortezomib) which is when they began experiencing CIPN symptoms. The participant then underwent an autologous stem cell transplantation and is currently receiving darzalex, which the participant states exacerbates symptoms of CIPN. The participant has a history of falls secondary to CIPN. The participant initiated a home-based exercise program consisting of resistance, aerobic, balance, and stretching exercises two to three times per week. Outcomes were assessed at baseline and 4 weeks after initiating the exercise program. Results The participant demonstrated increased step length and velocity during gait. EMG data suggested improvements in activation timing and strength of the gastrocnemius and tibialis anterior throughout the gait cycle, as well as improvements in lower-extremity co-contractions. Conclusion This was the first study to investigate the efficacy of a home-based exercise program on lower extremity muscle activation timing and gait characteristics of a cancer patient with CIPN that is currently receiving chemotherapy. The present case study demonstrated that a home-based exercise program may be a feasible intervention to help reduce co-contractions and improve the activation times and amplitudes of lower extremity muscles, which may help improve spatio-temporal gait parameters and reduce fall risk.

Objectives: The results of a few studies about the effects of ankle brace on muscles function during the performance of different tasks are contradictory. Moreover, the effect of brace on the co-contraction of ankle muscles is undiscovered. Therefore, the present study investigated the effect of brace usage on the ankle muscles activity and co-contraction during single-leg landing. Methods: Fifteen non-athletic males aged 22.3±1.09 years without any traumatic injury and abnormality of the lower limb participated in this study. Electromyography activity of the ankle muscles (tibialis anterior, lateral gastrocnemius, medial gastrocnemius, peroneus longus and soleus) and muscle co-contraction in the anteroposterior and mediolateral directions were compared between two single-leg landing conditions, in respect of braced and unbraced ankle. The subjects landed from a 60-cm height bench. For the normalization of electromyography amplitudes, maximal voluntary isometric contractions were recorded for each muscle. Paired Samples t-test was used to compare muscle activities and co-contractions between the two conditions of landing. Results: In general, the activity of selected ankle muscles was reduced in braced condition, compared to the unbraced condition (P

As we learn to perform a motor task with novel dynamics, the central nervous system must adapt motor commands and modify sensorimotor transformations. The objective of the current research is to identify the neural mechanisms underlying the adaptive process. It has been shown previously that an increase in muscle co-contraction is frequently associated with the initial phase of adaptation and that co-contraction is gradually reduced as performance improves. Our investigation focused on the neural substrates of muscle co-contraction during the course of motor adaptation using a resting-state fMRI approach in healthy human subjects of both genders. We analyzed the functional connectivity in resting-state networks during three phases of adaptation, corresponding to different muscle co-contraction levels and found that change in the strength of functional connectivity in one brain network was correlated with a metric of co-contraction, and in another with a metric of motor learning. We identified the cerebellum as the key component for regulating muscle co-contraction, especially its connection to the inferior parietal lobule, which was particularly prominent in early stage adaptation. A neural link between cerebellum, superior frontal gyrus and motor cortical regions was associated with reduction of co-contraction during later stages of adaptation. We also found reliable changes in the functional connectivity of a network involving primary motor cortex, superior parietal lobule and cerebellum that were specifically related to the motor learning. [ABSTRACT FROM AUTHOR]

Background: Exercise-based approaches have been a cornerstone of physiotherapy management of knee osteoarthritis for many years. However, clinical effects are considered small to modest and the need for continued adherence identified as a barrier to clinical efficacy. While exercise-based approaches focus on muscle strengthening, biomechanical research has identified that people with knee osteoarthritis over activate their muscles during functional tasks. Therefore, we aimed to create a new behavioural intervention, which integrated psychologically informed practice with biofeedback training to reduce muscle overactivity, and which was suitable for delivery by a physiotherapist.Methods: Through literature review, we created a framework linking theory from pain science with emerging biomechanical concepts related to overactivity of the knee muscles. Using recognised behaviour change theory, we then mapped a set of intervention components which were iteratively developed through ongoing testing and consultation with patients and physiotherapists.Results: The underlying framework incorporated ideas related to central sensitisation, motor responses to pain and also focused on the idea that increased knee muscle overactivity could result from postural compensation. Building on these ideas, we created an intervention with five components: making sense of pain, general relaxation, postural deconstruction, responding differently to pain and functional muscle retraining. The intervention incorporated a range of animated instructional videos to communicate concepts related to pain and biomechanical theory and also used EMG biofeedback to facilitate visualization of muscle patterns. User feedback was positive with patients describing the intervention as enabling them to "create a new normal" and to be "in control of their own treatment." Furthermore, large reductions in pain were observed from 11 patients who received a prototype version of the intervention.Conclusion: We have created a new intervention for knee osteoarthritis, designed to empower individuals with capability and motivation to change muscle activation patterns and beliefs associated with pain. We refer to this intervention as Cognitive Muscular Therapy. Preliminary feedback and clinical indications are positive, motivating future large-scale trials to understand potential efficacy. It is possible that this new approach could bring about improvements in the pain associated with knee osteoarthritis without the need for continued adherence to muscle strengthening programmes.Trial Registration: ISRCTN51913166 (Registered 24-02-2020, Retrospectively registered). [ABSTRACT FROM AUTHOR]

Age-related changes in presynaptic inhibition (PSI) have not been observed during gait initiation, which requires anticipatory postural adjustment (APA). As APA is centrally modulated and is impaired in older compared to young adults, here we aimed to study the presynaptic control and co-contraction levels in the ankle muscles during gait initiation in older compared to young adults. Fifteen older (age range 65-80 years) and 15 young adults (age range 19-30 years) performed a gait initiation task on a force platform under 3 conditions: (i) without electrical stimulation; (ii) test Hoffman reflex (H-reflex); and (iii) conditioned H-reflex. H-reflexes were evoked on the soleus muscle when the APA amplitude exceeded 10%-20% of the average baseline mediolateral force. Participants also performed quiet stance as a control task. Results showed that both age groups presented similar PSI levels during quiet stance (p = .941), while in the gait initiation older adults presented higher PSI levels, longer duration, and lower amplitude of APA than young adults (p < .05). Older adults presented higher co-contraction ratio in both tasks than young adults (p < .05). Correlations between the PSI levels and the APA amplitude (r = -0.61, p = .008), and between the PSI levels and the co-contraction ratio during gait initiation (r = -0.64, p = .005) were found for older adults only. APA amplitude explained 49% of the variance of the PSI levels (p = .003). Our findings suggest that older compared to young adults have increased presynaptic control to compensate for the decreased supraspinal modulation on impaired APAs during gait initiation. [ABSTRACT FROM AUTHOR]

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Coactivation of the knee extensors and flexors increases knee joint contact forces, which may lead to degradation of the articular surfaces. This study investigated the effect of neuromuscular fatigue induced by submaximal, repetitive, dynamic contractions on coactivation of knee musculature in young and middle-aged women. Data from 10 young women (24.6 ± 1.8 years) and 8 middle-aged women (55.4 ± 4.2 years) were analyzed. Measures included peak knee extension and flexion torques and the average amplitude of surface electromyography of rectus femoris and biceps femoris. Coactivation ratios were calculated from these activations. To induce fatigue, participants completed up to ten sets of 50 concentric knee extension and flexion contractions at 60°/s. A two-factor analysis of variance was used to determine the effect of age and fatigue. The young group showed higher peak torque compared with the middle-aged group (P < .001). During flexion, biceps femoris activity increased after fatigue when both groups were considered together (P = .018). During extension, biceps femoris activity was higher in the middle-aged than young group (P = .043). Middle-aged women exhibited a trend for greater coactivation during knee extension compared with young women (P = .066). This coactivation likely contributed to extension torque decrements in middle-aged women. [ABSTRACT FROM AUTHOR]

Background: The head, arms and trunk segment constitute a large proportion of the body's mass. Therefore, small alterations in trunk inclination may affect lower limb joint moments and muscle activation patterns. Although previous research has investigated the effect of changing frontal plane inclination of the trunk, it is not clear how increasing trunk flexion will impact on the activation of the lower limb muscles.Research Question: What is the effect of independently manipulating trunk flexion angle on lower limb kinematics, moments and muscle function?Methods: Gait analysis was carried out on 20 healthy people under four trunk flexion conditions: normal walking (NW), NW-5°, NW+5° and NW+10°. For the latter three conditions, a biofeedback approach was used to tightly control trunk flexion angle. A linear mixed model was used to investigate the effect of changing trunk flexion on joint angles, moments, and knee muscle activation.Results: There were clear increases in hip and ankle moments as trunk flexion was increased, but no change in knee moments. The results also showed a linear increase in knee flexor muscle activity and a corresponding increase in co-contraction as trunk flexion increased. Interestingly, there was a dramatic change in the profile of hamstring activity. In the medial hamstrings, this change led to a 100% increase in activation during early stance as flexion was increased by 5° from NW.Significance: This is the first study to demonstrate a strong dependence of knee flexor muscle activity on trunk flexion. This is important as people with knee osteoarthritis have been observed to walk with elevated muscle activation and this has been linked to increased joint loads. It is possible that these altered muscle patterns may result from increased trunk flexion during walking. [ABSTRACT FROM AUTHOR]

Introduction: Manual techniques have a special place in the treatment of osteoarthritis. However, the effects of these techniques have been investigated only on pain. Regarding this, the present study aimed to evaluate the effect of Mulligan manual technique on quadriceps and hamstrings muscles activity pattern. Materials & Methods: This quasi-experimental study was conducted on 38 volunteers with moderate knee osteoarthritis, selected through a non-randomized sampling method. The severity of osteoarthritis was determined based on the Kellgren-Lawrence grading system. In addition, the immediate effect of Mulligan manual technique on the pain and muscle amplitude in the pattern of muscle activity was investigated. The pain severity was measured using a numerical rating scale (i.e., 0-10). Furthermore, the evaluation of muscle amplitude was accomplished using surface electromyography. The data were analyzed using two-way ANOVA and paired sample t-test. Findings: The results of the study showed statistically significant changes in the mean scores of the investigated variables after the implementation of Mulligan manual technique (P

Purpose: A variation in squatting technique is using arms to actively push the bar up with the upper limbs which is common in bodybuilding. This study aimed to compare the Electromyography (EMG) activity of selected muscles during squat with and without upper limb assistance. Methods: This was a quasi-experimental study. Fifteen healthy male power lifters (using the convenience sampling method) participated in this study. Participants performed 2 sets of 5 repetitions while squatting 70% of their one-repetition maximum with and without upper limb assistance. Surface EMG signals were collected from 6 muscles using a wireless electromyography with a sampling frequency of 1200 Hz. The paired sample t test was used for statistical analyses at a significance level of P

It is unclear whether muscle coactivation during gait is altered early after stroke and among which muscles. We sought to characterize muscle coactivation during gait in subacute stroke subjects without hypertonia and explore the relationship with temporospatial parameters. In 70 stroke (23 ± 12 days post-onset) and 29 age-matched healthy subjects, surface electromyography signals were used to calculate coactivation magnitude and duration between rectus femoris and medial hamstring (knee antagonistic coactivation), tibialis anterior and medial gastrocnemius (ankle antagonistic coactivation), and rectus femoris and medial gastrocnemius (extensor synergistic coactivation) during early double-support (DS1), early single-support (SS1), late single-support (SS2), late double-support (DS2), and swing (SW). Compared to both free and very-slow speeds of controls, stroke subjects had bilaterally decreased ankle coactivation magnitude in SS2 and duration in SS1 and SS2 as well as increased extensor coactivation magnitude in DS2 and SW. Both non-paretic knee and ankle coactivation magnitudes in SS2 moderately correlated with most temporospatial parameters (|r| ≥ 0.40). Antagonistic and synergistic coactivation patterns of the knee and ankle muscles during gait are altered bilaterally in subacute stroke subjects without lower limb hypertonia suggesting impairments in motor control. Greater coactivation magnitudes in the non-paretic knee and both ankles during the terminal stance (SS2) are associated with the overall worse gait performance. Unlike previously reported excessive coactivation or no change in chronic stroke, bilaterally decreased and increased coactivation patterns are present in subacute stroke. These findings warrant longitudinal studies to examine the evolution of changes in muscle coactivation from subacute to chronic stroke. [ABSTRACT FROM AUTHOR]

Rhythmic masticatory muscle activity (RMMA), which is defined as three or more consecutive phasic bursts, accounts for a large part of sleep bruxism (SB). RMMA is thought to be characterized by co‐contraction, a jaw muscle activity in which jaw‐opening muscles contract during the active phase of jaw‐closing muscles, which is different from that during mastication. However, there has been limited information about co‐contraction. The aim of the present study was to clarify the amplitudes and patterns of jaw‐opening muscle activity during the active phase of jaw‐closing muscles in RMMA. Data from 14 healthy volunteers with bruxism, which was diagnosed by using polysomnographic recording with audio‐video, were analysed. RMMA with electromyographic amplitudes of more than two times the baseline amplitude was selected. From the selected RMMA, burst groups consisting of five or more consecutive phasic bursts, including tonic bursts, were selected for analyses. Electromyographic activities during gum chewing were also recorded before sleeping. The minimum, maximum and average value of the amplitudes of jaw‐opening muscle activity during the active phase of jaw‐closing muscles were calculated. Jaw‐opening muscle activity during the active phase of jaw‐closing muscles in RMMA was closer to the baseline than that in gum chewing. The minimum, maximum and average values of amplitudes of jaw‐opening muscle activity during the phase were significantly smaller than those of gum chewing. Contrary to our hypothesis prior to the study, the obtained results suggested that the pattern of electromyogram activity of jaw‐opening and jaw‐closing muscles in RMMA was not necessarily co‐contraction. [ABSTRACT FROM AUTHOR]

Introduction: There is limited data in the scientific literature using quantitative methods to assess response of golfer's cramp to intervention. The objective of this pilot study was to use quantitative measures to study the effect of propranolol and looking at the hole when putting.Methods: 14 golfers completed 50 10' putts (10 each x 5 conditions): two-handed looking at the ball, right hand only looking at the ball, two-handed looking at the hole, then following a single 10 mg oral dose of propranolol two-handed and right hand only putts looking at the ball. Quantitative measurements of putter movement and surface EMG to assess wrist muscle co-contraction were measured.Results: Based on video review of the putting, five golfers with dystonic golfer's cramp and nine with non-dystonic yips were compared. Those with dystonic golfer's cramp had more putts with the yips and yips with co-contraction when two-handed putting looking at the ball, no increase when putting right hand only, less smoothness of putter movement, and all of these improved following propranolol and when looking at the hole. The non-dystonic group had an increase in yipped putts and yipped putts with co-contraction putting right hand only and no improvement with either intervention.Conclusion: Yipped putts with co-contraction, right hand only putting, and smoothness of putter movement differed between dystonic golfer's cramp and non-dystonic yips. Propranolol and looking at the hole only improved dystonic golfer's cramp putting. This is the first pilot study of oral medication treatment for this task-specific dystonia. [ABSTRACT FROM AUTHOR]

Introduction: It is well established that obesity is associated with deterioration in postural control that may reduce obese adults' autonomy and increase risks of falls. However, neuromuscular mechanisms through which postural control alterations occur in obese adults remain unclear.Objective: To investigate the effects of obesity on muscle coactivation at the ankle joint during static and dynamic postural control.Materials and Methods: A control group (CG; n = 20; age = 32.5 ± 7.6 years; BMI = 22.4 ± 2.2 Kg/m²) and an obese group (OG; n = 20; age = 34.2 ± 5.6 years; BMI = 38.6 ± 4.1 Kg/m²) participated in this study. Static postural control was evaluated by center of pressure (CoP) displacements during quiet standing. Dynamic postural control was assessed by the maximal distance traveled by the CoP during a forward lean test. Electromyography activity data for the gastrocnemius medialis (GM), soleus (SOL) and tibialis anterior (TA) were collected during both quiet standing and forward lean tests. Muscle activities were used to calculate two separate coactivation indexes (CI) between ankle plantar and dorsal flexors (GM/TA and SOL/TA, respectively).Results: CoP displacements were higher in the OG than in the CG for quiet standing (p < 0.05). When leaning forward, the maximal distance of the CoP was higher in the CG than in the OG (p < 0.05). Only the CI value calculated for SOL/TA was higher in the OG than in the CG for both static and dynamic tasks (p < 0.05). The SOL/TA CI value in the OG was positively correlated with CoP displacements during quiet standing (r = 0.79; p < 0.05).Conclusion: Obesity increases muscle coactivation of the soleus and tibialis anterior muscles at the ankle joint during both static and dynamic postural control. This adaptive neuromuscular response may represent a joint stiffening strategy for enhancing stability. Consequently, increased ankle muscle coactivation could not be considered as a good adaptation in obese adults. [ABSTRACT FROM AUTHOR]

• Unloader brace did not change co-contraction of agonist and antagonist muscles. • Unloader brace produced changes in gluteal and gastrocnemius timing and amplitude, however, the clinical relevance is unclear. • There were no differences between adjusted and unadjusted brace conditions. To determine the immediate effects of a varus unloader knee brace on lower-limb electromyographic activity in individuals with lateral knee osteoarthritis and valgus malalignment after anterior cruciate ligament reconstruction. Electromyographic data were recorded in 19 individuals with lateral knee osteoarthritis and valgus malalignment after anterior cruciate ligament reconstruction during walking under three conditions: (i) no brace, (ii) unadjusted brace (no varus adjustment), and adjusted brace (varus adjustment). Variables of interest were statistically analyzed using repeated measures analysis of variance. There were no significant differences in muscle co-contraction between the three test conditions. The adjusted brace resulted in delayed offset of gluteus maximus (mean difference [95% CI]: 72 ms [24, 119]), and earlier onset of gluteus medius (59 ms [21, 97]) compared to no brace. The adjusted brace delayed onset of lateral gastrocnemius compared to no brace (53 ms [28, 78]) and the unadjusted brace (39 ms [7, 71]) and reduced average activation amplitude of gluteus maximus (−4 mV [−6, −1]) and lateral gastrocnemius (−9 mV [−16, −2]) compared to no brace. The unloader brace did not produce significant changes in muscle co-contraction in individuals with lateral knee osteoarthritis and valgus malalignment after anterior cruciate ligament reconstruction. Significant changes in gluteal and gastrocnemius muscle activation timing and amplitude were observed, however, it is not clear whether these changes are of clinical importance. [ABSTRACT FROM AUTHOR]

Objective: To compare hip joint contact forces (HJCF), hip muscle forces, and hip muscle co-contraction levels between individuals with mild-to-moderate hip osteoarthritis (OA) and healthy controls during walking.Design: Eighteen participants with mild-to-moderate hip OA and 23 healthy controls walked at a self-selected speed while motion capture and electromyographic data were synchronously collected. HJCF were computed using a calibrated electromyography-informed neuromusculoskeletal model. Hip joint contact forces, muscle forces, and co-contraction indices for flexor/extensor and adductor/abductor muscle groups were compared between groups using independent sample t-tests (P < 0.05).Results: There was no between-group difference in self-selected walking speed. On average, participants with hip OA walked with 11% lower first peak (mean difference 235 [95% confidence interval (CI) 57-413] N) and 22% lower second peak (mean difference 574 [95%CI 304-844] N) HJCF compared to controls. Hip muscle forces were also significantly lower in the hip OA compared to control group at first (mean difference 224 [95%CI 66-382] N) and second (mean difference 782 [95%CI 399-1164] N) peak HJCF. Participants with hip OA exhibited higher levels of hip muscle co-contraction in both flexor/extensor and adductor/abductor muscle groups. Consistent with existing literature, hip joint angles (extension, adduction) and external moments (flexion, extension, adduction) were lower in hip OA compared to controls.Conclusion: Lower HJCF were detected in mild-to-moderate hip OA, primarily due to lower hip muscle force production, and despite higher levels of hip muscle co-contraction. Findings suggest that lower loading of the hip joint during walking is a feature of mild-to-moderate hip OA, which could have implications for the pathogenesis of hip OA and/or disease progression. [ABSTRACT FROM AUTHOR]

This study aimed to assess modulation of lower leg muscle reflex excitability and co-contraction during unipedal balancing on compliant surfaces in young and older adults. Twenty healthy adults (ten aged 18–30 years and ten aged 65–80 years) were recruited. Soleus muscle H-reflexes were elicited by electrical stimulation of the tibial nerve, while participants stood unipedally on a robot-controlled balance platform, simulating different levels of surface compliance. In addition, electromyographic data (EMG) of soleus (SOL), tibialis anterior (TA), and peroneus longus (PL) and full-body 3D kinematic data were collected. The mean absolute center of mass velocity was determined as a measure of balance performance. Soleus H-reflex data were analyzed in terms of the amplitude related to the M wave and the background EMG activity 100 ms prior to the stimulation. The relative duration of co-contraction was calculated for soleus and tibialis anterior, as well as for peroneus longus and tibialis anterior. Center of mass velocity was significantly higher in older adults compared to young adults ( p < 0.001) and increased with increasing surface compliance in both groups ( p < 0.001) . The soleus H-reflex gain decreased with surface compliance in young adults (p = 0.003) , while co-contraction increased (p S O L , T A = 0.003 a n d p P L , T A < 0.001) . Older adults did not show such modulations, but showed overall lower H-reflex gains (p < 0.001) and higher co-contraction than young adults (p S O L , T A < 0.001 a n d p P L , T A = 0.002) . These results suggest an overall shift in balance control from the spinal level to supraspinal levels in older adults, which also occurred in young adults when balancing at more compliant surfaces. [ABSTRACT FROM AUTHOR]

BACKGROUND: The majority of common agility tests include pre-planned change of direction (COD) maneuvers which require muscular coordination. However, muscular coordination in terms of organization of co-activated antagonistic muscle pairs in COD maneuvers have not been studied. OBJECTIVE: To evaluate muscle coordination by analyzing co-contraction at knee and ankle during three agility tests and to investigate the relationships between muscle coordination and test completion time. METHOD: Thirteen healthy young male subjects (22.1 ± 1.9 years) participated in the study. Surface EMG and acceleration signals were used to calculate co-contraction index (CCI) for selected antagonistic muscle pairs of ankle and knee joints during COD maneuvers in agility tests. RESULTS: The findings indicated that concurrent activation costs a delay to complete the test faster. CCI was higher at right ankle and left knee and showed an increasing trend with advancing the phase when the test requires multiple CODs. CONCLUSIONS: Minimizing co-contraction would result in faster movement, however, there might be a trade-off between joint stiffness and test performance depending on changes in neuromuscular factors such as altered motor control strategies due to strength imbalances or occurrence of fatigue. [ABSTRACT FROM AUTHOR]

Individuals with cerebral palsy can have weak and poorly coordinated ankle plantar flexor muscles that contribute to inefficient walking patterns. Previous studies attempting to improve plantar flexor function have had inconsistent effects on mobility, likely due to a lack of task-specificity. The goal of this study was to develop, validate, and test the feasibility and neuromuscular response of a novel wearable adaptive resistance platform to increase activity of the plantar flexors during the propulsive phase of gait. We recruited eight individuals with spastic cerebral palsy to walk with adaptive plantar flexor resistance provided from an untethered exoskeleton. The resistance system and protocol was safe and feasible for all of our participants. Controller validation demonstrated our ability to provide resistance that proportionally- and instantaneously-adapted to the biological ankle moment (R = 0.92 ± 0.04). Following acclimation to resistance (0.16 ± 0.02 Nm/kg), more-affected limbs exhibited a 45 ± 35% increase in plantar flexor activity (p = 0.02), a 26 ± 24% decrease in dorsiflexor activity (p < 0.05), and a 46 ± 25% decrease in co-contraction (tibialis anterior and soleus) (p = 0.02) during the stance phase. This adaptive resistance system warrants further investigation for use in a longitudinal intervention study. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the study was to investigate the role of training in improvement of balance control in older adults with mild cognitive impairment.Methods: Older adults (mean age 78) with mild cognitive impairment (MCI) and cognitively intact older adults (mean age 72) were exposed to self-initiated perturbations while performing bilateral shoulder flexion task before and after a single training session consisting of throwing a medicine ball. EMG activity of six trunk and lower limb muscles was recorded. Muscle onsets, integrals of EMG, and muscle co-contraction (C) and reciprocal (R) activation indices were calculated and analyzed during the anticipatory and compensatory phases of postural control.Results: Anticipatory postural adjustments (APAs) were observed in both groups.  Individuals with MCI, as compared to controls, had higher level of co-contraction of muscles. The training resulted in enhancement of the generation of APAs in individuals with MCI seen as earlier onset of leg and trunk muscle activity prior to the bilateral arm flexion task. While smaller co-contraction of muscles post-training was seen in both the groups, the effect of a single training session was significant in control subjects only.Conclusions: The outcome of the exploratory study suggests that perturbation-based training could be used to improve balance control in older adults with and without mild cognitive impairment. [ABSTRACT FROM AUTHOR]

The purpose of this study was to identify alterations in preparatory muscle activation patterns across different drop heights in female athletes. Sixteen female high school volleyball players performed the drop vertical jump from three different drop heights. Surface electromyography of the quadriceps and hamstrings were collected during the movement trials. As the drop height increased, muscle activation of the quadriceps during preparatory phase also increased (p < .05). However, the hamstrings activation showed no similar increases relative to drop height. Female athletes appear to preferentially rely on increased quadriceps activation, without an increase in hamstrings activation, with increased plyometric intensity. The resultant decreased activation ratio of the hamstrings relative to quadriceps before landing may represent altered dynamic knee stability and may contribute to the increased risk of ACL injury in female athletes. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to evaluate differences in hamstring activation during lower body resistance training exercises. This study also sought to assess differences in hamstring-to-quadriceps muscle activation ratios and gender differences therein. Methods: A randomized repeated measures design was used to compare six resistance training exercises that are commonly believed to train the hamstrings, including the squat, seated leg curl, stiff leg dead lift, single leg stiff leg dead lift, good morning, and Russian curl. Subjects included 34 college athletes. Outcome measures included the biceps femoris (H) and rectus femoris (Q) electromyography (EMG) and the H-to-Q EMG ratio, for each exercise. Results: Main effects were found for the H (P < 0.001) and Q (P < 0.001). Post hoc analysis identified the specific differences between exercises. In addition, main effects were found for the H-to-Q ratio when analyzed for all subjects (P < 0.001). Further analysis revealed that women achieved between 53.9 to 89.5% of the H-to-Q activation ratios of men, for the exercises assessed. In a separate analysis of strength matched women and men, women achieved between 35.9 to 76.0% of the H-to-Q ratios of men, for these exercises. Conclusions: Hamstring resistance training exercises offer differing degrees of H and Q activation and ratios. Women compared with men, are less able to activate the hamstrings and/or more able to activate the quadriceps. Women may require disproportionately greater training for the hamstrings compared with the quadriceps. [ABSTRACT FROM AUTHOR]

The timing of the effects of botulinum toxin A on spastic muscles is not yet fully clarified. The goal of this study was to follow the temporal changes of surface electromyographic activity of lower limb muscles during walking, after a therapeutic dose of botulinum toxin A injected into the calf muscles of children with spastic cerebral palsy. A group of children with spastic equinus foot was administered botulinum toxin A into the gastrocnemius medialis and lateralis muscles. Surface electromyographic activity of the tibialis anterior, gastrocnemius medialis, rectus femoris and medial hamstrings, was recorded before botulinum toxin A injections and after 4, 8, and 16 weeks. Children walked on ground and on a treadmill at an incline of 0% and 12%. The area of electromyographic activity and the index of muscle co-contraction were calculated for specific segments of gait cycle. Botulinum toxin A did not modify the speed of gait on ground. ANOVA showed significant differences in electromyography during the stance phase segments with a maximum decrease between 4 and 8 weeks' post botulinum toxin A and a full recovery at 16 weeks. A significant co-contraction of rectus femoris/gastrocnemius medialis, between 0 and 20% and 35–50% of the gait cycle, was observed from the 4th to the 8th week post- botulinum toxin A for both treadmill settings. The temporal identification of deterioration/recovery of electromyographic activity as well as of muscle co-contractions, could be key elements in a rehabilitation program planning combined with botulinum toxin A. • Gastrocnemius shows a U shaped myoelectric trend after botulinum toxin (73 characters) • Before botulinum toxin, gastrocnemius adapts to different walking tasks (74 characters) • After botulinum toxin, gastrocnemius does not adapt to different walking tasks (81 characters) • Co-contraction of rectus femoris occurs when gastrocnemius is weakened (74 characters) • Resistance training should be started after the 8th week post botulinum toxin (81 characters) [ABSTRACT FROM AUTHOR]

In the context of neuro-orthopedic pathologies affecting walking and thus patients' quality of life, understanding the mechanisms of gait deviations and identifying the causal motor impairments is of primary importance. Beside other approaches, neuromusculoskeletal simulations may be used to provide insight into this matter. To the best of our knowledge, no computational framework exists in the literature that allows for predictive simulations featuring muscle co-contractions, and the introduction of various types of perturbations during both healthy and pathological gait types. The aim of this preliminary study was to adapt a recently proposed EMG-marker tracking optimization process to a lower limb musculoskeletal model during equinus gait, a multiphase problem with contact forces. The resulting optimization method tracking EMG, ground reactions forces, and marker trajectories allowed an accurate reproduction of joint kinematics (average error of 5.4 ± 3.3 mm for pelvis translations, and 1.9 ± 1.3° for pelvis rotation and joint angles) and ensured good temporal agreement in muscle activity (the concordance between estimated and measured excitations was 76.8 ± 5.3 %) in a relatively fast process (3.88 ± 1.04 h). We have also highlighted that the tracking of ground reaction forces was possible and accurate (average error of 17.3 ± 5.5 N), even without the use of a complex foot-ground contact model.

Introduction: Excessive co-contraction interferes with smooth joint movement. One mechanism is the failure of reciprocal inhibition against antagonists during joint movement. Reciprocal inhibition has been investigated using joint torque as an index of intensity during co-contraction. However, contraction intensity as an index of co-contraction intensity has not been investigated. In this study, we aimed to evaluate the influence of changes in contraction intensity during co-contraction on reciprocal inhibition.Methods: We established eight stimulus conditions in 20 healthy adult males to investigate the influence of changes in contraction intensity during co-contraction on reciprocal inhibition. These stimulus conditions comprised a conditioning stimulus-test stimulation interval (C–T interval) of -2, 0, 1, 2, 3, 4, or 5 ms plus a test stimulus without a conditioning stimulus (single). Co-contraction of the tibialis anterior and soleus muscles at the same as contraction intensity was examined at rest and at 5, 15, and 30% maximal voluntary contraction (MVC).Results: At 5 and 15% MVC in the co-contraction task, the H-reflex amplitude was significantly decreased compared with single stimulation at a 2-ms C–T interval. At 30% MVC, there was no significant difference compared with single stimulation at a 2-ms C–T interval. At a 5-ms C–T interval, the H-reflex amplitude at 30% MVC was significantly reduced compared with that at rest.Discussion: The findings indicated that during co-contraction, reciprocal Ia inhibition worked at 5 and 15% MVC. Contrary inhibition of reciprocal Ia inhibition did not apparently work at 30% MVC, and presynaptic inhibition (D1 inhibition) might work.

The anterior cruciate ligament is the primary structural restraint to tibial anterior shear force. The anterior force occurring at the knee during landing contributes to anterior cruciate ligament injury risk, but it cannot be directly measured experimentally. The objective of this study was to develop electromyography-informed musculoskeletal simulations of the drop vertical jump motor task and assess the contribution of knee muscle forces to tibial anterior shear force. In this cross-sectional study, musculoskeletal simulations were used to estimate the muscle forces of thirteen female athletes performing a drop vertical jump using an electromyography-informed method. Muscle activation and knee loads that resulted from these simulations were compared to the results obtained with the more common approach of minimization of muscle effort (optimization-based method). Quadriceps–hamstrings and quadriceps–gastrocnemius co-contractions were progressively increased and their contribution to anterior shear force was quantified. The electromyography-informed method produced co-contraction indexes more consistent with electromyography data than the optimization-based method. The muscles that presented the largest contribution to peak anterior shear force were the gastrocnemii, likely from their wrapping around the posterior aspect of the tibia. The quadriceps–hamstring co-contraction provided a protective effect on the ACL and reduced peak anterior shear force by 292 N with a co-contraction index increase of 25% from baseline (31%), whereas a quadriceps–gastrocnemius co-contraction index of 61% increased peak anterior shear force by 797 N compared to baseline (42%). An increase in gastrocnemius contraction, which might be required to protect the ankle from the impact with the ground, produced a large quadriceps–gastrocnemius co-activation, increasing peak anterior shear force. A better understanding of each muscle's contribution to anterior shear force and, consequently, anterior cruciate ligament tension may inform subject-specific injury prevention programs and rehabilitation protocols. [ABSTRACT FROM AUTHOR]

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• EMG-EMG coherence for the assessment of quadriceps-hamstrings (Q-H) co-contraction. • 60–90% of tested legs showed significant Q-H gamma-band coherence during squatting. • Females showed higher Q-H coherence than males during single-leg squatting. • Injury history was associated with reduced Q-H coherence in males but not females. The purpose of this study was to determine the degree of co-contraction as per electromyographic gamma-band intermuscular coherence of the quadricep (Q) and hamstring (H) muscles during single-leg squatting (SLS), and to assess the influence of sex and self-reported knee complaints on the association between knee injury history and medial and lateral Q-H intermuscular coherence. Participants included 34 individuals who suffered a youth sport-related intra-articular knee injury 3–12 years previously, and 37 individuals with no knee injury history. Surface electromyographic signals were recorded from medial and lateral thigh muscles bilaterally to determine the gamma-band (30–60 Hz) intermuscular coherence between medial and lateral Q-H muscle pairs during SLS. Multivariable linear regression (α = 0.05) was performed to investigate the relationship between knee injury history (main exposure) and medial and lateral Q-H coherence (outcome) while accounting for the influence of sex and self-reported knee pain and symptoms (covariates). The median age of participants was 25 (range 18–30) and 67% were female. Q-H gamma-band coherence was present for 60–90% of legs. Medial and lateral Q-H coherence was higher in females compared to males. There was no evidence for an association between medial Q-H coherence, knee injury history, knee pain, or symptoms. There was evidence for an association between knee injury history and lateral Q-H coherence, which was modified by sex such that previously injured males demonstrated reduced Q-H coherence compared to uninjured males. These finding suggest that females demonstrate a more pronounced Q-H co-contraction strategy during a SLS than males regardless of knee injury history. Further, that male who suffered a youth sport-related knee injury 3–12 years previously demonstrate less Q-H co-contraction during a SLS than uninjured males. The mechanisms behind differences in neuromuscular control between males and females as well as previously injured and uninjured males require further investigation. [ABSTRACT FROM AUTHOR]

In the context of neuro-orthopedic pathologies affecting walking and thus patients' quality of life, understanding the mechanisms of gait deviations and identifying the causal motor impairments is of primary importance. Beside other approaches, neuromusculoskeletal simulations may be used to provide insight into this matter. To the best of our knowledge, no computational framework exists in the literature that allows for predictive simulations featuring muscle co-contractions, and the introduction of various types of perturbations during both healthy and pathological gait types. The aim of this preliminary study was to adapt a recently proposed EMG-marker tracking optimization process to a lower limb musculoskeletal model during equinus gait, a multiphase problem with contact forces. The resulting optimization method tracking EMG, ground reactions forces, and marker trajectories allowed an accurate reproduction of joint kinematics (average error of 5.4 ± 3.3 mm for pelvis translations, and 1.9 ± 1.3° for pelvis rotation and joint angles) and ensured good temporal agreement in muscle activity (the concordance between estimated and measured excitations was 76.8 ± 5.3 %) in a relatively fast process (3.88 ± 1.04 h). We have also highlighted that the tracking of ground reaction forces was possible and accurate (average error of 17.3 ± 5.5 N), even without the use of a complex foot-ground contact model. [ABSTRACT FROM AUTHOR]

Heightened co-activation of the quadriceps and hamstrings has been reported following anterior cruciate ligament reconstruction during various tasks, and may contribute to post-traumatic osteoarthritis risk. However, it is unclear if this phenomenon occurs during walking or how co-activation influences gait biomechanics linked to changes in joint health. Co-activation and gait biomechanics were assessed in 50 individuals with ACLR and 25 healthy controls. Biomechanical outcomes included knee flexion displacement, peak vertical ground reaction force magnitude and rate, peak internal knee extension and valgus moments and rates, sagittal knee stiffness, and the heelstrike transient. Co-activation was calculated for the flexors and extensors collectively (i.e. composite), the medial musculature, and the lateral musculature. Composite co-activation was greater in the ACLR limb compared to the contralateral limb and the control cohort during the preparatory and heelstrike phases of gait, and co-activation of the medial musculature was greater in the ACLR limb compared to the control cohort during the heelstrike phase. Greater co-activation in multiple gait phases was associated with less knee flexion displacement (r = −0.293 to −0.377), smaller peak vertical ground reaction force magnitude (r = −0.291), smaller peak internal knee extension moment (r = −0.291 to −0.328), and greater peak internal knee valgus moment (r = 0.317). Individuals with ACLR displayed heightened co-activation during walking which was associated with biomechanical outcomes that have been linked to negative changes in joint health following ACLR. These data suggest that excessive co-activation may contribute to the mechanical pathogenesis of post-traumatic osteoarthritis. ClinicalTrials.gov Identifier: NCT02605876. • Heightened co-activation may contribute to osteoarthritis risk after ACL injury. • Unclear if this phenomenon occurs during gait or if it influences biomechanics • Co-activation was greater in the ACLR limb vs. contralateral and controls. • Greater co-activation associated with biomechanics linked to poor joint health • Excessive co-activation may contribute to the mechanical pathogenesis of PTOA. [ABSTRACT FROM AUTHOR]

Medial and lateral hamstrings are known for their capacity to promote internal or external rotation of the knee. Apart from implant geometry, increased co-contraction to a larger share of either the medial or lateral hamstrings has the potential to contribute to the restricted knee internal rotation especially under consideration of cruciate ligament substituting compared to cruciate ligament retaining knee endoprosthesis designs. Hence, the purpose of the study was to evaluate, whether increased co-contraction of the hamstrings contribute to the impaired knee internal rotation in total and unicondylar knee arthroplasty patients during level and decline walking. Knee joint angles were calculated using an inverse kinematics model in Anybody. Muscle activity was examined of the semitendinosus and biceps femoris. Knee internal rotation was constraint in the operated compared to the non-operated limb only in the total knee arthroplasty group during decline slope walking. Co-contraction values revealed no statistically significant differences between the operated and non-operated limb during the limited knee internal rotation period of time (59–94% of stance). Biceps femoris activity was significantly reduced (69–71% of stance) in the operated limb in the total knee arthroplasty group during decline slope walking. Contrary to the proposed mechanism, aspects other than co-contraction between semitendinosus and biceps femoris are involved in the impaired transverse plane knee motion. These include implant congruency and probably friction. Unexpectedly, the biceps femoris did not compensate the absence of the anterior cruciate ligament with increased muscular activity in the operated limb of the total knee arthroplasty group. • Knee internal rotation is not limited due to hamstrings co-contraction in TKA. • Decline walking exposed restricted knee internal rotation only in the TKA group. • No difference in knee flexion angles between affected and not affected limbs. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the interaction between the activity ratio and the muscles of the lower extremity muscles according to the treadmill walking speed. The subjects measured the MVIC (Maximum Voluntary Isomeric Contraction) of the tibialis anterior, semitendinosus, medial gastrocnemius, biceps femoris using wireless surface electromyography. After walking for 1 minute at the speed of 3km/h, 4km/h, and 5km/h on the treadmill, muscle activities of the tibialis anterior, semitendinosus, medial gastrocnemius, biceps femoris. % MVIC (muscle activity/MVIC x 100) was used for the generalization of the measurements. In the treadmill walking at the speed of 3km/h, 4km/h, and 5km/h, the muscle activity ratios of the tibialis anterior, semitendinosus, medial gastrocnemius and the biceps femoris are as follows. There was a significant difference in muscle activity (P <0.05) in the tibialis anterior, medial gastrocnemius and the biceps femoris at 3km/h speed, 4km/h speed, 3km/h speed and 5km/h speed. There was a significant difference (P <0.05) in the semitendinosus muscle activity ratio between the 3 km/h and 4km/h speed walk, 3km/h speed and 5km/h speed walk, 4km/h speed walk and 5km/h speed walk. As the walking speed increased to 5km/h, the semitendinosus connected to the knee joint led to the gait rather than the ankle joint, so that it was found that the lower and the lower shoulder tend to walk with the tendency of bending and inner rotation. [ABSTRACT FROM AUTHOR]

The spinal reciprocal inhibition during co-contraction remains unclear. Reports on the reciprocal Ia and D1 inhibitions in the co-contraction are lacking, and a point about the muscle activity amount during co-contraction is unclear. This study aimed to clarify the influence of changes in the ratio of soleus (Sol) and tibialis anterior (TA) muscle activities in co-contraction on reciprocal Ia and D1 inhibitions. Twenty healthy adults were subjected to four stimulatory conditions: a conditioning stimulus–test stimulation interval (CTI) of − 2, 2, or 20 ms or a test stimulus without a conditioning stimulus (single). Co-contraction [change in (Sol)/(TA) activity] was examined at task A, 0%/0% maximal voluntary contraction (MVC); task B, 5%/5% MVC; task C, 15%/15% MVC; task D, 5%/15% MVC; and task E, 15%/5% MVC. At 2-ms CTI, the H-reflex amplitude value was significantly lower in tasks A, B, C, and D than in the single condition. Among the tasks, the H-reflex amplitude values were lower for A, B, C, and D than for E. At 20-ms CTI, the H-reflex amplitude was significantly lower in tasks A, B, C, D, and E. Among the tasks, the H-reflex amplitude was significantly lower from task A and B to task E. The change in the muscle activity ratio during co-contraction could modulate reciprocal Ia inhibition depending on the Sol/TA muscle activity ratio. D1 inhibition at rest did not differ significantly when the Sol/TA ratio was equal or when TA muscle activity was high. During co-contraction with high Sol muscle activity, D1 inhibition decreased from rest. [ABSTRACT FROM AUTHOR]

Voluntary toe walking in adults is characterized by feedforward control of ankle muscles in order to ensure optimal stability of the ankle joint at ground impact. Toe walking is frequently observed in children with cerebral palsy, but the mechanisms involved have not been clarified. Here, we investigated maturation of voluntary toe walking in typically-developing children and typically-developed adults and compared it to involuntary toe walking in children with cerebral palsy. Twenty-eight children with cerebral palsy (age 3-14 years), 24 typically-developing children (age 2-14 years) and 15 adults (mean age 30.7 years) participated in the study. EMG activity was measured from the tibialis anterior and soleus muscles together with knee and ankle joint position during treadmill walking. In typically-developed adults, low step-to-step variability of the drop of the heel after ground impact was correlated with low tibialis anterior and high soleus EMG with no significant coupling between the antagonist muscle EMGs. Typically-developing children showed a significant age-related decline in EMG amplitude reaching an adult level at 10-12 years of age. The youngest typically-developing children showed a broad peak EMG-EMG synchronization (>100 ms) associated with large 5-15 Hz coherence between antagonist muscle activities. EMG coherence declined with age and at the age of 10-12 years no correlation was observed similar to adults. This reduction in coherence was closely related to improved step-to-step stability of the ankle joint position. Children with cerebral palsy generally showed lower EMG levels than typically-developing children and larger step-to-step variability in ankle joint position. In contrast to typically-developing children, children with cerebral palsy showed no age-related decline in tibialis anterior EMG amplitude. Motor unit synchronization and 5-15 Hz coherence between antagonist EMGs was observed more frequently in children with cerebral palsy when compared to typically-developing children and in contrast to typically-developing participants there was no age-related decline. We conclude that typically-developing children develop mature feedforward control of ankle muscle activity as they age, such that at age 10-12 years there is little agonist-antagonist muscle co-contraction around the time of foot-ground contact during toe walking. Children with cerebral palsy, in contrast, continue to co-contract agonist and antagonist ankle muscles when toe walking. We speculate that children with cerebral palsy maintain a co-contraction activation pattern when toe walking due to weak muscles and insufficient motor and sensory signalling necessary for optimization of feedforward motor programs. These findings are important for understanding of the pathophysiology and treatment of toe walking. [ABSTRACT FROM AUTHOR]

Copyright of German Journal of Sports Medicine / Deutsche Zeitschrift fur Sportmedizin is the property of Verein zur Forderung der Sportmedizin Hannover e.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background and objectives: The maximal abdominal contraction maneuver (MACM) was designed as an effective and efficient breathing exercise to increase the stability of the spinal joint. However, it has not been determined whether MACM is more effective and efficient than the maximal expiration method. Thus, the present study was undertaken to investigate whole abdominal muscle thickness changes after MACM. Materials and Methods: Thirty healthy subjects (17 males and 13 females) participated in this study. An experimental comparison between MACM and the maximal expiration task was conducted by measuring the change of abdominal muscle thickness such as the transverse abdominis (TrA), internal oblique (IO), external oblique (EO) and rectus abdominis (RA) using ultrasound images. Results: The results indicated that MACM resulted in significantly greater muscle thickness increases of the TrA and RA than the maximal expiration exercise (p < 0.05). Conclusion: MACM provided better exercise than the maximal expiration exercise in terms of increasing spine stability, at least from a co-contraction perspective.

Purpose: Less attention has been paid to the electromyographic activity of the lower extremity muscles, which is considered as an essential part of the kinetic studies on the gait of mentally retarded individuals. Hence, the study aims at determining the surface electromyography characteristics of the lower extremity muscles of mentally retarded adolescents during walking. Methods: It is a causal-comparative study. Fifteen mentally retarded and 15 normal adolescents with an age range of 10 to 14 years participated in this study. To record the activities of vastus medialis, vastus lateralis, biceps femoris, semi-tendinosus, tibialis anterior, long peroneal, medial gastrocnemius, and soleus muscles, sEMG was employed during the stance phase of gait. For the data analysis, an independent sample t-test was conducted using SPSS version 18. Results: The results revealed that the mentally retarded adolescents had higher level of biceps femoris muscle activity in the heel contact sub-phase (P=0.016) compared to the normal group. Also, the vastus medialis (P=0.015) and the long peroneal (P=0.026) muscles showed higher EMG activity. Furthermore, their vastus lateralis (P=0.039) and Soleus (P=0.002), and vastus medialis (P=0.045) muscles demonstrated higher and lower activities, respectively. The co-contraction rate of medial gastrocnemius and anterior tibialis muscles during the heel contact was higher (P=0.040) in individuals with mental retardation compared to the healthy group. Conclusion: It can be concluded that the mentally retarded individuals use different muscle activation patterns in comparison to healthy people. As a result, special attention should be given to the functioning of their lower extremity muscles during the corrective power exercises.

We examined the effects of attentional focus cues on maximal voluntary force output of the elbow flexors and the underlying physiological mechanisms. Eleven males participated in two randomized experimental sessions. In each session, four randomized blocks of three maximal voluntary contractions (MVC) were performed. The blocks consisted of two externally and two internally attentional focus cued blocks. In one of the sessions, corticospinal excitability (CSE) was measured. During the stimulation session transcranial magnetic, transmastoid and Erb’s point stimulations were used to induce motor evoked potentials (MEPs), cervicomedullary MEP (CMEPs) and maximal muscle action potential (Mmax), respectively in the biceps brachii. Across both sessions forces were lower (p = 0.024) under the internal (282.4 ± 60.3 N) compared to the external condition (310.7 ± 11.3 N). Muscle co-activation was greater (p = 0.016) under the internal (26.3 ± 11.5%) compared with the external condition (21.5 ± 9.4%). There was no change in CSE. Across both sessions, force measurements were lower (p = 0.033) during the stimulation (279.0 ± 47.1 N) compared with the no-stimulation session (314.1 ± 57.5 N). In conclusion, external focus increased force, likely due to reduced co-activation. Stimulating the corticospinal pathway may confound attentional focus. The stimulations may distract participants from the cues and/or disrupt areas of the cortex responsible for attention and focus.

Abstract Background Patients with knee osteoarthritis often present with varus thrust and muscular co-contraction during gait. It is unclear if these adaptations are related. The objective was to examine the relationship between muscle co-contraction and varus thrust during gait in patients with knee osteoarthritis and to determine if these relationships are modulated by disease severity or history of knee ligament rupture. Methods Participants (n = 42, 23 women, mean age 58 years) with knee osteoarthritis completed gait trials at self-selected speeds. Varus thrust was measured with an eight camera motion capture system sampled at 100 Hz. Co-contraction ratios were measured with surface electromyography sampled at 2000 Hz over the quadriceps, hamstrings, and gastrocnemius. Disease severity was measured on radiographs and history of anterior cruciate ligament rupture was confirmed on magnetic resonance imaging. Linear regression analyses examined the relationship between varus thrust and co-contraction ratios after controlling for radiographic disease severity and history of anterior cruciate ligament rupture. Findings Higher vastus lateralis–lateral hamstring (b = 0.081, P < 0.001; R2 = 0.353) and vastus medialis–medial hamstring (b = 0.063, P = 0.028; R2 = 0.168) co-contraction ratios were associated with greater varus thrust. Quadriceps-gastrocnemius co-contractions ratios were not related to varus thrust (P > 0.05). Radiographic disease severity or history of anterior cruciate ligament injury did not significantly contribute to regression models. Interpretation Greater quadriceps-hamstring co-contraction is associated with greater varus thrust in patients with knee osteoarthritis. Potential explanations include increased co-contraction may provide stability or there is a proprioceptive reflex that is independent of any stabilizing role. Research is needed to test these hypotheses. Highlights • Varus thrust and muscle co-contraction exists in patients with knee osteoarthritis. • These variables, measured during gait, have not been compared. • Quadriceps-hamstring co-contraction ratios were directly related to varus thrust. • Co-contraction during gait might stiffen the knee or it could be a reflex. [ABSTRACT FROM AUTHOR]

Purpose: To determine whether quantitative methods could separate golfers with a possible dystonic cause of the "yips" from those that appear to be nondystonic. Methods: Twenty-seven golfers completed 10 two-handed and 10 right hand–only putts. Surface EMG assessed forearm muscle co-contraction and motion detectors monitored wrist and putter movements. Based on a videotape review, golfers were grouped into those with yips of dystonic etiology, those with the yips nondystonic, and those with no yips. Results: On video review of two-handed putting, five golfers had yips that appeared to be dystonic, nine had yips that did not appear to be dystonic, and 13 had no yips. During two-handed putting co-occurrence of a yipped putt and wrist flexor/extensor and/or pronator/supinator co-contraction was significantly more frequent in those with dystonic yips. The dystonic group had no increase in the number of yipped putts or yips with co-contraction when putting right hand only, whereas the nondystonic group had significantly more yipped putts and more yipped putts with co-contraction with right hand only. Conclusions: Quantitative methods were identified that appear to identify golfers with a dystonic etiology for the yips. It is not just the frequency of yips nor just specific motion patterns alone, rather it is also a combination of yips with co-occurring co-contraction when putting with two hands, and then right hand only, that distinguished this possible etiology. Despite being a small study, identifying a dystonic pattern, even in a nonpressure indoor setting, may aid in assessment and possible monitoring of treatment. [ABSTRACT FROM AUTHOR]

Background Enhancement of arm adductor activity during abduction (ie, adductor co-contraction), may be effective in the treatment of subacromial pain syndrome (SAPS). We assessed whether an increase of adductor co-contraction is associated with a favorable course of SAPS. Methods At baseline and after nearly 4 years of follow-up, electromyography of the latissimus dorsi (LD), teres major (TM), pectoralis major, and deltoid muscle was obtained during isometric abduction and adduction tasks in 26 patients with SAPS. Changes in co-contraction were assessed with change in the activation ratio (Δ AR). The AR ranges between −1 and 1, where lower values indicate more co-contraction. Clinical course was determined from an anchor question (reduced, persistent, or increased complaints), the visual analog scale for pain (VAS), and the Western Ontario Rotator Cuff score (WORC). Results In patients indicating persistent complaints (31%), the VAS and WORC remained stable. In patients who indicated reduced complaints (69%), the VAS reduced (z score, −3.4; P =.001) and WORC increased (z score, 3.6; P <.001). Unchanged ARs associated with complaints persistence, whereas decreased AR of the LD (Δ AR LD , −0.21; 95% confidence interval [CI], −0.36 to −0.06) and TM (ΔAR TM , −0.17; 95% CI, −0.34 to −0.00) coincided with reduced complaints. There was a significant between-group difference in Δ AR LD (−0.35; 95% CI, −0.60 to 0.10) and Δ AR TM (−0.36; 95% CI, −0.66 to –0.05). Conclusions Increased co-contraction of the LD and TM is associated with a favorable course of SAPS. This may be explained by widening of the subacromial space accomplished by adductor co-contraction. [ABSTRACT FROM AUTHOR]

Abstract A reliable evaluation of muscle forces in the human body is highly desirable for several applications in both clinical and research contexts. Several models of muscle force distribution based on non-invasive measurements have been proposed since 1836 (Weber and Weber, 1836), amongst which Crowninshield's model (Crowninshield and Brand, 1981), which maximizes a cost-function representing the muscle fiber endurance, is the most popular. It is worth noting that Crowninshield's model is the most widely adopted notwithstanding its major limitations of physiological coherence. Forster et al. (2004) pointed out that "these (conventional) criteria however do not predict co-contraction adequately". Besides, electromyographic (EMG)-driven models have been proposed to assess individual muscle forces, which have not been broadly adopted due to their complexity and the need for a calibration before each test. In this context, a cost function based on kinematic and electromyographic data could provide the advantage of being physiologically more coherent with muscle activations compared to conventional cost-functions based on kinematics solely, and easier to use than the EMG-driven models. The objective of this study is to propose the first cost-function based on kinematics and electromyographic data to quantify muscle forces. When applying this new cost-function on a database of upper limb motions data of 17 subjects, healthy or with cerebral palsy, the muscle force prediction of the proposed model was 17.74% more coherent with the EMG pattern than the prediction of Crowninshield's model. And on average, these results were more consistent whether the subjects were healthy or with cerebral palsy. In conclusion, we propose this cost-function for the quantification of muscle forces. [ABSTRACT FROM AUTHOR]

An adaptable method of computing muscle co-activity is presented. Instantaneous muscle activities from multiple muscles are reduced into commonality and activity level dimensions. Both dimensions are weighted independently and combined into a co-activation measure, U. Myoelectric data from relaxed and braced simulated rear vehicle impacts were used to compare U to two existing co-activity measures in muscle pair and multi-muscle cases. U showed greater sensitivity in the muscle pair case and could better discriminate the relaxed and braced conditions in the multi-muscle case than previous measures. The flexibility of U allowed tailoring to reflect the current purpose. [ABSTRACT FROM AUTHOR]

Based on previous evidence that whole-body vibration (WBV) affects pathways involved in disynaptic reciprocal inhibition (DRI), the present hypothesis-driven experiment aimed to assess the acute effects of WBV on DRI and co-contraction. DRI from ankle dorsiflexors to plantar flexors was investigated during submaximal dorsiflexion before and after 1 min of WBV. With electromyography, musculus soleus (SOL) H-reflex depression following a conditioning stimulation of the peroneal nerve (1.1x motor threshold for the musculus tibialis anterior, TA) was assessed and co-contraction was calculated. After WBV, DRI was significantly increased (+4%, p < 0.05). SOL (-13%, p < 0.05) and TA (-6%, p < 0.05) activities were significantly reduced; co-contraction tended to be diminished (-8%, p = 0.05). Dorsiflexion torque remained unchanged. After WBV, DRI increased during submaximal isometric contraction in healthy subjects. The simultaneous SOL relaxation and TA contraction indicate that a more economic movement execution is of functional significance for WBV application in clinical and athletic treatment. [ABSTRACT FROM AUTHOR]