RT - Journal Article T1 - Effect of knee extension force reduction induced by fatigue on muscle co-contraction JF - Research-in-Sport-Medicine-and-Technology YR - 2021 JO - Research-in-Sport-Medicine-and-Technology VO - 19 IS - 21 UR - http://jsmt.khu.ac.ir/article-1-416-en.html SP - 65 EP - 75 K1 - Muscle force K1 - Electromyography K1 - Fatigue K1 - Co-contraction AB - 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 LA eng UL http://jsmt.khu.ac.ir/article-1-416-en.html M3 10.29252/jsmt.19.1.65 ER -