Comparison of electrical and co-contraction activity of selected lower limb muscles during manual load lifting with three different technique

Introduction and Aim: 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. Methods: 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. Results: 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). Conclusion: 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.