co-contraction

Co-contraction can be defined as the simultaneous activation of agonist and antagonist muscles around a joint. Co-contraction plays a fundamental role in movement control during physiological motor learning-related activities. The aim of the present study was to investigate the relationship between maximum heart rate (MHR) during an exhaustive fatigue protocol and co-contraction of the ankle joint muscles in overweight individuals compared to normal-weight individuals.

The sample consisted of two groups of 12 individuals (n=24), divided into overweight and normal-weight groups. The activity of the ankle joint muscles, including the tibialis anterior and gastrocnemius, was recorded during running using electromyography (EMG). MHR was also recorded using a Polar device. Pearson’s correlation coefficient was used to determine the correlation between variables at a significance level of 0.05.

The results indicate that changes in general and directed co-contraction of the ankle joint muscles in both phases of running did not change significantly before and after the induction of the fatigue protocol. Furthermore, no significant correlation was seen between MHR during the exhaustive fatigue protocol and changes in general and directed co-contraction in phase one and two of running
(P > 0.05).

This study revealed that MHR during exhaustive exercise does not significantly affect ankle muscle co-contraction. The lack of correlation between these two variables suggests that the neuromuscular response to fatigue may be independent of cardiovascular stress and body weight status.

Today, there is a disagreement about the effect of various stretching movements on the performance of athletes. Therefore, the aim of this study was to investigate the acute effect of static and dynamic stretching on muscle activity and co-contraction of scapular stabilizer muscles during pull up in gymnasts.

According to the inclusion and exclusion criteria, 15 professional gymnasts with an age (23.25 ± 2.57), height (170.93 ± 5.88), and weight (64.54 ± 5/06) were selected as research samples and divided into three subgroups (each 5).In the pre-test, subjects performed pull up and muscle activity of serratus anterior, upper trapezius, middle trapezius and lower trapezius muscles was measured using a biometric electromyography device. Then each subgroup performed a different stretching protocol in each session and a post-test was performed similar to the pre-test. Repeated measures analysis of variance, Bonferroni post hoc test and paired t-test were used to test the hypotheses.

The results showed that static and dynamic stretching caused a significant decrease and increase of muscle activity in both concentric and eccentric phases. 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 stretch and dynamic stretch and between dynamic stretch and control on co-contraction of serratus anterior and middle trapezius muscles in two concentric and eccentric phases.

The results showed that the co-contraction of serratus anterior and middle trapezius muscles decreased after using dynamic stretching. Therefore, considering the importance of muscle co-contraction in the occurrence of shoulder joint injuries and in order to prevent injuries in the shoulder joint of gymnasts, it is suggested that coaches and gymnasts should use dynamic stretching exercises more carefully.

Different surfaces have different effects on body mechanics during walking. The aim of this study was to evaluate ankle joint co-contraction in individuals with healthy and supinated feet during walking on artificial turf and stable ground.

This study was a semi-experimental and laboratory one. The statistical population included 10 individuals with supinated feet (mean age of 22.1± 2.2 years) and 10 individuals with healthy feet (mean age of 24.2± 3.3 years). The electrical activity of selected lower limb muscles was recorded using electromyography system during walking. Two ways ANOVA with repeated measure test was used for statistical analysis using SPSS 20 software at significant level of 0.05.

Results showed that the main effect of surface (P=0.035) and group (P=0.000) on general ankle co-contraction was significant during loading phase. General ankle co-contraction during loading phase while walking on artificial turf was greater than walking on the ground. Differences between other directional and general co-contraction components in other phases during walking on artificial turf and stable ground were not significant (P<0.05).

General co-contraction values of muscles during walking on artificial turf were greater than walking on the stable ground. Increased general co-contraction may be associated with instability of the surface. Nevertheless, to prove this as well as possible, it is necessary to conduct more research in the future with larger statistical populations.

Jumping and landing are important activities in performing sports movements that strongly affect muscle activity. People with Genu Valgum are prone to extensive damage to the knee joint due to structural changes. The aim of this study was to investigate the effect of short-term use of protective knee brace on ankle and knee joint co-contractions in people with genu valgum during jumping and landing.

The present study was a quasi-experimental and laboratory study. 10 boys with genu valgum in the experimental group and 10 healthy boys who did not have any lower limb disorders were selected as the control group. The knee brace used was BeActive model 1031. Electrical activity of selected muscles was recorded by electromyography (Biometrics LTD, UK). For statistical analysis, SPSS V21 software and analysis of variance (ANOVA) with repeated measures were used at a significant level of P<0.05.

The results showed no significant difference between the pre-test and post-test of the genu valgum group (P = 0.063, t = 2.276). Examination of all general co-contractions of ankle joint in the control group who used knee brace showed a significant decrease in post-test during pre-test comparison (P = 0.001, t = 6.831).

According to the results of the research, it can be concluded that the decrease in co-contraction of the knee joint indicates a decrease in the simultaneous activity of the muscles supporting the knee joint. Probably, the knee brace has been able to play a supporting and protective role in the knee joint, and as a result, it has led to a decrease in the activity of the supporting muscles around the joint.

Low back pain is a musculoskeletal disorder with an annual prevalence of 18.6%. The aim of the present study was to evaluate the effect of rehabilitation with medicine ball on directed and general co-contraction of knee joint muscles in low back patients during walking,

The present study was a clinical trial. The statistical population of the present study included patients with low back pain in the age range of 20-30 years in Ardabil in 1399. Participants in the study included 20 men with low back pain, who were randomly assigned (names were placed in a bag and identified randomly and one among extracts and groups) in two The exercise group and the control group were divided. The training group performed 12 sessions of strengthening exercises of the central muscles of the body with the beta medicine ball. Selected muscle activity during walking was recorded in two groups during pre- and post-test

Findings demonstrated that general contraction during loading and mid-stance phases increased significantly at post-test than that pre-test. Paired wise comparison demonstrated that directed flexor/extensor knee joint contraction during push off phase increased significantly.

Exercise therapy with medicine ball improved directed and general co-contraction of knee joint muscles in low back pain patients during walking.

Diabetes is related to dysfunction and damage of various organs, especially blood vessels, nerves, and heart. The aim of this study was to evaluate the effect of gait training on ankle joint co-contraction in diabetic patients with without neuropathy.

The method of the present study was quasi-experimental. The statistical population of the present study included 24 people who were randomly and equally divided into experimental and control groups, 12 in each. The experimental group performed walking exercises for 8 weeks and the control group did not do any activity during this period. To calculate the general and directed co-contraction, first the electromyography activity of the Gastrocnemius and tibialis anterior muscles was recorded by an 8-channel electromyography device (Bio System, UK) with a surface electrode. Biometrics Data LITE software and a filter pass between 10 and 450 Hz was used to record. To normalize the electromyography signals, the root mean square (RMS) information of each muscle was divided by the maximum isometric maximum co-contraction of that muscle to normalize the data and then multiplied by one hundred. Then, the data of the two groups were statistically analyzed by two-way analysis of variance using SPSS software version 24.

The results showed that the general co-contraction during the loading phase in the experimental group in the post-test phase increased significantly compared to the pre-test. There was a significant decrease in the experimental group compared to the pre-test group in mean directed co-contraction during loading phase (p = 0.001), support (p <0.001), toe off (p = 0.008) and swing (p = 0.001) and was close to zero.

The results of the present study showed that gait Trainings are effective on general and directional ankle joint co-contraction in diabetic patients without neuropathy, and increased co-contraction in the ankle joint, which can have beneficial effects on joint stability during walking.

Ankle injuries are one of the most common musculoskeletal injuries in atheletes. Proper landing after jumping leads to the preparation for the next skill as well as prevention of various ankle injuries. This study aims to compare the electrical activity of selected ankle muscles in athletes duirng landing from different heights.

 This is a comparative study. Participants were 15 athletes (Mean age= 18.23 ± 2.3 years, mean height= 183.190 ± 6.3 cm, mean weight= 64.72 ±14.12 kg) with 3-5 years of experience in championship competitions. The landing skill was assessed from different heights (50%, 75%, 100% of maximum jump height). Electrical activity of selected ankle joint muscles (Gastrocnemius and Soleus) was recorded using an eight-channel BIOMED electromyography device with 96.34% validity and 91.29% reliability. Mean and standard deviation were used to describe the data, Shapiro-Wilk test was used to evaluate the normality of data distribution, and repeated measures analysis of variance was used to compare the collected data between groups followed by Bonferroni post hoc test. The significance level was set at 0.05.

 There was no significant difference in co-contraction of medial/lateral gastrocnemius and soleus muscles after jumping from three different heights. The peak contraction amplitude of the lateral gastrocnemius muscle was significantly different between the heights 50-75% (P= 0.006) and 50-100% (P= 0.002). The peak contraction amplitude of the medial gastrocnemius muscle was also significantly different between the heights 50-75% (P= 0.002) and 50-100% (P= 0.007). The peak contraction amplitude of soleus muscles was significantly different between the heights 75-100% (P=0.013) and 50-100% (P= 0.17).

 There is an increase in the contractile activity of selected ankle muscles in the anterior-posterior plane caused by the increase in jump height and subsequent landing due to the optimal use of appropriate strategies to control the eccentric muscle contraction and the extensor torque of the ankle joint by increasing the electrical muscle activity during the ground contact, resulted in the prevention of injury to the ankle joint. Coaches and athletes can use these results to adopt training methods to strengthen these ankle muscles by considering the optimal implementation of landing skills with an injury prevention approach.

 The study aimed to evaluate the effects of motion control shoes on knee joint co-contraction in overweight individuals with flat feet.

15 overweight females with a navicular drop greater than 10 mm were selected with available sampling. Demographic characteristics of participants include Mean±SD age: 26.8±2.5 years, height: 1.7±0.1 m, weight: 82.5±3.2 kg, and Body Mass Index: 28.2±1.1 kg/m2. This study was done during running with both control (Supernova control, Adidas) and motion control (Supernovacushion, Adidas) shoes. An electromyography system recorded selected muscles’ electrical activity and then computed co-contraction values. Paired sample t-test was used for statistical analysis.

 Finding demonstrated that during the loading phase, the directed co-contraction of vastus medialis/lateral while using motion control shoes was greater than control shoes (P=0.035). Also, mediolateral-directed knee joint co-contraction while running with a motion control shoe was greater than the control shoe during the push-off phase (P=0.020). 

Motion control shoes improved directed co-contraction in overweight individuals with flat feet, especially in the frontal plane that could modify imposed knee joint loads.

 older adults show high levels of co-contraction in lower extremities’ muscles due to the deterioration of the neuromuscular and sensory motor systems. Increased co-contraction leads to disruption of daily motor activities, especially movements in which joint stability is critical; therefore, it is important to pay attention to training programs to strengthen muscles and increase intramuscular coordination in older adults. The aim of this study was to investigate the effect of unstable resistance training with and without blood flow restriction on ankle muscles’ co-contraction of older adults.

 27 older adults (62 ± 1.5 years old) were assigned into three groups of unstable resistance training without blood flow restriction, unstable resistance training with blood flow restriction (72± 9 mm Hg) and control. The training program consisted of three to four sets of 15 repetitions of body weight squats for four weeks and three sessions per each week, which were gradually added to the program by 5% of each person's body weight. Pre- and post- intervention, the electromyography signals of Tibialis Anterior and soleus muscles were recorded during walking in order to determine the rates of agonist and antagonist activity and muscles’ co-contraction. For data analysis, repeated measures analysis of variance and analysis of covariance tests with Bonferroni post hoc test were used at 0.05 of level of significance.

 The results showed that in post-test, the activity of the Tibialis Anterior muscle of both training groups was significantly increased compared to pre-test. Also, statistically significant difference was found in co-contraction rates of both groups in post-test. The results of Bonferroni post hoc test showed a statistically significant difference in reduction of co-contraction rates between the resistance training group with blood flow restriction and the control group (P=0.015) and between resistance training group without blood flow restriction with the control group (P=0.005). But no statistically significant difference was found between the two training groups.

 Resistance training on unstable surface with and without blood flow restriction is associated with increased agonist muscle activity, which leads to a decrease in ankle muscles’ co-contraction in older adults.

In the past few decades, exercise has been promoted with increasing interest for the treatment of back pain. Therefore, the present study aimed to investigate the effect of rehabilitation exercises with medicine beta balls on the directional and general contraction of ankle joint muscles in patients with low back pain during walking.

The present study was a clinical trial. The statistical population was patients with low back pain in the age range of 20-30 years in Ardabil in 1399.  Twenty men with low back pain were randomly divided into exercise and control groups. The intervention group performed 12 sessions of strengthening exercises of the central muscles of the body with the beta medicine ball. The activity of selected muscles was recorded during walking pre-and post-test in two groups. A two-way analysis of variance with repeated measures was used for statistical analysis.

The results showed that the interactive effect of time and group on the directional contraction values of the ankle joint during the middle phase was significant (P = 0.020). Post hoc test showed that the values of all directional contraction of the ankle joint increased significantly during the middle phase in the experimental group.  

Increasing the values of directional contraction after the training period during the middle phase of reliance in the experimental group can be associated with more joint stability and less vulnerability

Diabetes is associated with dysfunction, and failure of various organs, especially the nerves, heart, and blood vessels. This study aimed to evaluate the effect of aerobic training on ankle joint co-contraction in patients with Diabetic neuropathy during walking.

The statistical sample of the present study included 20 patients (age: 54.9±7.3, Body mass index: 28.4±5.1) with diabetic neuropathy in the experimental group and 20 patients (age: 54.1±7.1, Body mass index: 28.5±5.1) with diabetic neuropathy in the control group who were selected by convenience sampling. The electrical activity of selected lower limb muscles was recorded using an electromyography system during walking. The experimental group did aerobic training for eight weeks (three sessions per week). The 2-ways ANOVA with repeated measures was used for statistical analysis.

The results demonstrated lower general ankle co-contraction in the post-test loading phase than the pre-test in the experimental group (P=0.001). Other components of directed co-contraction in all phases and general co-contraction in different phases did not demonstrate any significant differences after training protocol (P>0.05).

Damage to the peripheral nerve due to diabetic neuropathy in patients with moderate neuropathy causes abnormal co-contraction contentment of lower limb muscles during walking; therefore, lowering the general ankle co-contraction results in proper control of the lower limbs, which could decrease the likelihood of injury and falls in patients.

Manual handling of loads is a complex dynamic task that involves the upper and lower limbs. Manual handling of loads in sports and daily activities can expose people to unfavorable physical conditions and lead to injury. The study aimed to compare the electrical activity and co-contraction of selected lower limb muscles during manual load lifting with three different techniques.

This study was a quasi-experimental study. Eighteen healthy male subjects were randomly selected (age: 26.2±1.68 years, weight: 73.6±6.56 kg, height: 176.5±7.51cm). The subjects performed the task of manual load lifting by three different techniques (Squat, Stoop and Freestyle). Electrical activity of the rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, gastrocnemius medialis and tibialis anterior muscles were recorded during lifting with use of an electromyographic device.

The intensity of quadriceps muscle; rectus femoris, vastus lateralis, vastus medialis activity in stoop technique was significantly less (P=0.012, P=0.023, P=0.034) and the intensity of hamstring muscle activity in stoop technique was significantly more than two other techniques (P<0.05). Also, the general co-contraction in the stoop technique is lower than the squat (P=0.001) and freestyle technique (P=0.009). Extensori-flexori directional co-contraction in stoop technique was significantly lower than the two other techniques (P<0.05).

According to the results, the Squat technique is a better technique for manual lifting of load than the freestyle and stoop techniques, and proper use of muscles around the knee joint reduces the mechanical forces and the risk of injury to this joint.

Fatigue can change the biomechanical parameters of movement by Inability to produce enough force to perform a certain motor task (1). Abnormalities in the lower extremities (such as the pronated foot) can adversely affect the biomechanics of human movements (such as walking) and cause unstable symptoms in the joints and lack of co-contraction in the lower extremities (2). In a dynamic position such as walking, from a biomechanical point of view, the simultaneous function of the agonist and antagonist muscles around the joint as well as the loads on the joint are important to maintain the position and stability of the joint (13). Due to structural changes such as increased internal rotation of the tibia and abduction of the anterior leg at the pronated foot and thus reduced impact absorption when running, fatigue may cause more pressure to be applied to the active muscles and structures involved in walking during the stance phase (10). Considering the role of co-contraction of the muscles around the knee in the control and stability of the knee joint during walking, and also due to the lack of sufficient studies on co-contraction while walking, Therefore, a more detailed study of this issue is necessary after fatigue (16). Also, recognizing the effect of fatigue on muscle co-contraction of the muscles around the knee during walking can provide a new perspective for biomechanics and other rehabilitation specialists to better implement the rehabilitation program (15). Therefore, The main purpose of this study was the effect of exhaustive fatigue protocol on knee muscle co-contraction in healthy and pronated foot individuals during walking.

Fourteen young men with pronated feet With average (age 24.66±3.29 years and height 170.52±11.66 cm and weight 66.56±15.42 kg) and 14 healthy feet With mean (age 25.27±3.14 years and height 173.7±6.2 cm and weight 72.3±4.7 kg), participated in the study. The fatigue protocol of this study was to run at the heart rate deflection point (HRDP) level until fatigue. HRDP is defined as the point of deviation of the heart rate from a straight line in examining the relationship between workload and heart rate, which is used as a criterion for planning the intensity of aerobic exercise (20). Two foot switches were used to record the time characteristics of the stance stage, ie contact of the heel with the ground and separation of the toes from the ground, one of them was installed in the outer part of the posterior part of the heel and the other was installed on the first sole-toe joint. In the classification of different stages of walking from the moment of heel contact with the ground to the moment of toe contact with the ground as the heel contact stage, the time interval between toe contact with the ground to the heel separation as the middle stage of establishment and the time interval between heel separation from the ground and toe separation (23). Electromyography activities of the Rectus femoris (RF), Vastus medialis or VM, Vastus lateralis (VL), Semitendinosus (ST), Biceps femoris (BF), Gastrocnemius medialis (GM), and Tibialis anterior (TA) muscles in two stages before and after fatigue protocol (pre-test and post-test) using (Biometrics Ltd, UK) 8-channel wireless and bipolar surface electrodes Model of surface electrode pairs Bipolar Ag / AgCl (25 mm center-to-center distance, 100 MPa input impedance, Common-mode rejection ratio (CMRR) less than 110 dB at 50 to 60 Hz) were recorded (25).To evaluate the normality of the data, Shapirovilk test was used. To compare the data between the pre-test and post-test stages of the two groups analysis of variance with repeated measures(ANOVA) and Bonferroni post hoc test were used. The statistical analysis was performed using the SPSS software version 25, the significance level was considered(p≤0.05).

The results showed that after fatigue in both pronated and healthy foot groups, during the pre-test and post-test stages of walking, general knee joint co-contraction in the mid-stance phase (p=0.014) and the swing phase (p=0.032) Significantly decreased. and the Flexor/extensor directed co-contraction of the knee joint during the heel contact phase phase in the pronated foot compared to the healthy foot group, during the pre-test and post-test stages, was significantly reduced (p=0.031). and the the internal/external directed co-contraction of the knee joint during the mid-stance phase phase in the pronated foot compared to the healthy foot group, during the pre-test and post-test stages, was significantly reduced (p=0.048).Another part of the results of the present study showed that after fatigue in both pronated and healthy foot groups, during the pre-test and post-test stages of walking, the Vastus medialis / Vastus lateralis directed co-contraction of the knee joint during the push off phase, Significantly increased (p=0.012). The other components did not show any significant differences.

The general knee co-contraction of both pronated and healthy foot groups Significantly decreased. it seems that fatigue that occurs as a result of changes in muscle function, by changing the locomotor system can change the mechanics of movement and joints while running. Therefore, perhaps this difference in muscle activity observed after fatigue is one of the mechanisms for changes in joint mechanics and reduction of general contraction.An increase in directional co-contraction in people with pronated feet indicates an increase in pressure on the internal structures of the ankle. Long-term running may expose the internal structures of the foot to the risk of overload and injury. In general, one of the factors in the change in the degree of stability and loads of the joint can be the contraction of the muscles around the joints (22). This means that if there is a decrease in joint stability, the contraction of the muscles around the joint will change to stabilize the joint. In other words, the change in contraction is a sign of instability in the joint. Therefore, it is suggested that in investigating the effects of fatigue on walking mechanics and the incidence of walking injuries in people with pronated foot, muscle co-contraction in the joints should be considered to determine whether these changes to compensate for traumatic mechanical changes after fatigue created or related to muscle adaptation to long-term activity.

Fatigue and deformities in the lower extremities such as the pronate foot can adversely affect the biomechanics of human movements and walking. Under fatigue conditions, the biomechanical differences of pronate and healthy feet are more easily identified. Therefore, the aim of this study was to investigate the effect of helpless fatigue protocol on all ankle muscle contractions in pronate and healthy individuals during walking.

Fourteen young men with pronate feet and 14 healthy men participated in this study. Electromyographic activity of selected muscles was recorded before and after the fatigue protocol. Data were analyzed using SPSS software and two-way analysis of variance with repeated measures.

The results showed that after fatigue, all general contractions in pronate and healthy foot groups decreased significantly during the heel contact phase (P=0.040). Also, the directional contraction in both groups increased significantly during the heel separation phase (P=0.022) and oscillation (P=0.039) in the pretest compared to the posttest. The other components did not show any significant differences.

The change in all the contractions of the muscles around the ankle joint indicates an increase in pressure on its internal structures. Abnormal anatomical changes in the feet of these people after fatigue may put them at risk for overload or injury. Therefore, it is suggested that in examining the effects of fatigue on gait mechanics and the incidence of gait injuries, attention should be paid to all muscle contractions in the joints.

Fatigue and abnormalities in the lower extremities, such as the pronated foot, can adversely affect the biomechanics of human movements such as running, leading to a lack of muscle contraction and unstable symptoms in the joints of the lower extremities (knees). Therefore, the main purpose of this study was to investigate the effect of exhaustive protocol on knee muscle co-contraction in pronated and healthy individuals while running.

Fourteen young men with pronated feet and 14 healthy feet participated in the study. Electromyography activities of the selected muscles before and after fatigue protocol were recorded. The statistical analysis was performed using the SPSS software and repeated measures analysis of variance (ANOVA) (P ≤0.05).

Findings in the pronated foot compared with the healthy foot group showed that the knee general co-contraction during the mid-stance phase (P = 0.026, d = 0.81) and swing (P = 0.046, d = 0.81) and Vastuslateralis/vastusmedialis directed co-contraction of the knee was significantly lower during the heel contact phase (P = 0.049, d = 0.81). Flexural/extensor directed co-contraction in comparison of pretest to posttest during heel propulsion phase in both groups of pronated foot (P = 0.037, d = 0.81) and healthy foot (P = 0.037, 0.81 = d) decreased significantly. The other components did not show any significant differences.

The co-contraction of the examined muscles in the knee joint has decreased in pronated foot in different stages of stance compared to the healthy foot group. This may be due to the over-activity of a group of muscles to overcome the instability of the knee and to prevent the extra movements of this joint when fatigue occurs, and it is also possible that this over-activity of a group of muscles has affected the running mechanics of individual with pronated foot and at different stages of the running cycle caused additional pressure on the knee joint and the musculoskeletal system in the knee joint loses its ability to properly absorb shock when running, increasing joint looseness and the risk of joint damage due to fatigue Increase.