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Showing 3 results for Co-Contraction

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Volume 0, Issue 0 (11-2019)

Background: Despite the relation between nervous system function, fatigue, and co-contraction, it seems that the difference in co-contraction changes due to fatigue induced by sprinting and endurance running probably indicates the dominance of one source of fatigue (central/peripheral) over the other. This study aimed to compare the effect of fatigue induced by endurance running and sprinting on the knee muscle co-contraction in active young women with the approach of identifying the origin of fatigue.
Methodology: Thirteen active young women volunteers (20-30 years, BMI 20-25kg/m2) were randomly selected. Subjects performed fatigue protocols during two sessions with four days of rest in between. The electrical activity of the vastus-medialis and vastus-lateralis muscles was recorded using an electromyography device before and after two stages of running 400-meter (with 100% effort) and 3000-meter (with 50% effort) during the execution of knee extension movement and co-contraction was calculated with the formula. Two-way repeated measure was used to analyze the data.
Results: There was no significant difference between the co-contraction of the selected muscles before and after sprinting (p=0.3) and endurance running (p=0.19) and no significant difference (p=0.85) between the difference in co-contraction rate in the pre-test and post-test of sprinting and endurance running.
Conclusion: Since there was no difference between the effect of fatigue caused by sprinting and endurance running on the co-contraction of the selected muscles, likely, the involvement of central factors in the appearance of fatigue caused by 400-meter sprinting and 3000-meter endurance running is similar and insignificant. The emergence of fatigue after the implementation of both protocols may be more due to environmental factors.
Seyed Hossein Hosseinimehr, Mehrdad Anbarian,
Volume 16, Issue 16 (12-2018)

The purpose of this study was to compare the effect of shoulder abduction angles, dominant and non-dominant arm and external loading on co-contraction ratio during arm abduction in scapular plane in overhead athletes and non-athletes. 10 swimmers, 10 handball players and 10 tennis players and ten non-athletes voluntarily participated in this study. Electromyography activity of shoulder muscles (middle and anterior deltoid; upper, middle and lower trapezius; infraspinatus, serratus anterior and latissimus dorsi) during dynamic and static arm abduction in 3 different angles (0-45º in 1second and holding it for 3 seconds, 0-90º in 2 seconds and holding it for 3 seconds, 0-135º in 1 second and holding it for 3 seconds) was recorded for dominant and non-dominant arm in loading and non-loading conditions. Co-contraction ratio of shoulder muscles was calculated for both groups. Findings indicated external loading, shoulder dominance and abduction angles had significant effect on shoulder muscles co-contraction ratio during (0-45º, 0-90º, 0-135º) and holding shoulder elevation in scapular plane (45º, 90º, 135º),  also there was significant difference in shoulder muscles co-contraction ratio among four groups during and holding elevation in scapular plane (p≤0.05). Significant differences in shoulder muscles co-contraction ratio among athletes group and between athletes and non-athletes may be related to sport demands and adaptation to exercises and extensive use of upper limb as well. 

Dr. Leila Ghazaleh, Mis Fahimeh Bakhshizadeh, Dr. Rana Fayazmilani,
Volume 19, Issue 21 (9-2021)

It is necessary to examine the changes of muscle co-contraction in different percent of fatigue-induced force reduction. The present study aims to investigate the effect of fatigue-induced force reduction of knee extension on muscle co-contraction. Ten healthy and active women aged 26.10±2.99 years performed fatigue protocol including 5 seconds of maximal voluntary isometric contraction (MVIC) of the knee extension and a 5-second rest. Muscle co-contraction was calculated for each subject in the repetitions in which the MVIC force was reduced by 10, 20, 30, 40 and 50% as compared to the pre-fatigue MVIC force. Knee extension force and muscle activity measured by Isokinetic and electromyography apparatus, respectively. The difference between co-contraction of vastus lateralis and medialis in different percentages of force reduction was not statistically significant. The co-contraction of rectus femoris and biceps femoris increased by 40 and 50% of force reduction compared to pre-fatigue co-contraction (P<0.01). Co-contraction of biceps femoris and vastus lateralis increased by 20, 30, and 40%, as well as co-contraction of biceps femoris  and vastus medialis increased 40% of the force reduction, compared to pre-fatigue co-contraction (P <0.05). The results, overall, showed that the change of co-contraction during fatigue is influenced by the selected muscle and the rate of force reduction. This finding can help researchers decide how neuromuscular fatigue effects on muscle co-contraction

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