comparison of generalised and directed cocontraction of knee joint muscles during four different movements to strengthen the quadriceps

Different movements have a role in strengthening the quadriceps muscles based on knee joint co-contraction, hamstring to quadriceps and vastus medialis to vastus lateralis muscles activity ratios. this provides useful information about each movement’s role in rehabilitating patients with anterior cruciate ligament injury, osteoarthritis and patellofemoral pain syndrome. this study compared the rate of generalized and directed co-contraction of knee joint muscles during free weight, smith’s one-legged and two-legged machine squats and deadlift movement. fourteen healthy power lifters (mean age of 26 ± 7 years old) participated in this study. a portable electromyography system with six pairs of bipolar surface electrodes was used to record the activity of the gastrocnemious medialis, long head of biceps femoris, semitendinosus, vastus lateralis, rectus femoris, and vastus medialis muscles at a sampling frequency of 1200 hz. the participants had enough experience to perform the four movements. the participants carried out each movement five times at intensity equal to 50% of one-repetition-maximum level. repeated- measure analysis of variance was used for statistical analysis. rate of medial co-contraction was higher in deadlift movement compared to smith one- legged machine (p = 0.042) and free weight squats (p = 0.044), respectively. ratio of hamstring to quadriceps muscles activity was higher during deadlift movement compared to free weight squat (p= 0.022). the generalized co-contraction value at the knee joint was the lowest in deadlift movement and highest in smith one-legged machine squat. to strengthen quadriceps muscles in people suffering from anterior cruciate injury, deadlift movement is more effective than free weight squat. smith one-legged machine squat is more effective than the other three movements for athletes who want to strengthen muscular groups.