Final answer:
Muscles work in antagonistic pairs where one muscle, the flexor, contracts to move a bone toward the body, while the other, the extensor, moves it away. Examples include the biceps and triceps in the upper arm and the quadriceps and hamstrings in the thighs.
Step-by-step explanation:
Skeletal Muscle Pairs and Movement
In the human body, muscle groups work in an antagonistic pair to facilitate movement, meaning that while one muscle contracts, its partner muscle relaxes. The muscle that contracts to move the bone toward the body is known as the flexor, whereas the one that contracts to move the bone away from the body is called the extensor. The classic example is the biceps and triceps muscles in the upper arm; the biceps act as the flexor to bend the arm at the elbow, and the triceps act as the extensor to straighten it.
Other examples of antagonistic muscle pairs include the quadriceps and hamstrings in the thighs, where the quadriceps are the extensors and the hamstrings are the flexors. This coordinated action is essential for smooth and controlled movements throughout the body.
Different types of body movements, such as abduction and adduction, which refer to moving a limb away from or towards the body's midline, also involve the activity of antagonistic muscles. Knowing how different muscles function as flexors or extensors helps us understand body mechanics and the actions we perform in daily life and sports.