The flexor muscles are muscles that bend joints while extensor muscles are muscles that straighten these joints. These muscles are connected to the bone by tendons. Ligaments do not connect muscles to the bone, instead, it connects bones to another bone. Flexor and extensor are what you call antagonistic muscle pairs that oppose the function of each other.
Examples of flexor-extensor pairs in the body are the biceps and triceps, quadriceps and hamstrings, pectorals and trapezius, gluteus maximus and hip flexors, and tibialis anterior and extensor hallicus longus.
Movement of each pair:
• biceps and triceps ,(located in the arms) - Biceps are muscles that contract bends the elbow towards the body, while triceps will relax the muscles or straighten them.
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• quadriceps and hamstrings, (located in the knees area) - Quadriceps bends and hamstrings straightens. It helps you bend your knee.
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• pectorals and trapezius, (located in the chest to shoulders area) - The pair will move the arms towards the body and away from the body. It gives us the ability to swim. The pectorals are major muscles of the chest area that can both extend and bend since it is joined in with two different heads. The trapezius is located at the upper back area to the shoulders of the body and aids the pectorals in the extension and bending of the arms.
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• gluteus maximus and hip flexors, (located in the hip area) - It is important for standing, walking, and staying upright. Gluteus maximus is the major muscle in the thigh that straightens the lower limbs. Hip flexors are a collection of flexor muscles that bend the thigh forward.
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• Tibialis anterior and extensor hallicus longus ,(located in the foot) - The tibialis anterior flexes the ankle away from the foot while the extensor hallicus longus bends the foot upward towards the body.