Saha ExerScience LAB

When someone walks or runs or stand up from a chair, the quadriceps and the hamstrings contract at the same time. His/her quadriceps and hamstring muscle are antagonists, producing opposing movements (hip extension and knee flexion for the hamstrings, and hip flexion and knee extension for the quadriceps). Ideally these antagonistic contractions should cancel each other out! Why doesn’t someone just get locked during the movement at hips and knees? Here opposing muscles firing together. The resultant of these actions should stop the movement!..But in reality it does not happen so! What could be the reason?