
Concept explainers
Identify as many pairs of antagonistic muscle groups in the body as you can. If you cannot name them, point out the probable location of the flexor and extensor of each group.

To determine: The pairs of antagonistic muscle groups present in the human body.
Introduction: Muscles are the bundle of fibrous tissue present in the body of an organism. The muscles are responsible for the contraction, movements and maintaining the position of different body parts.
Explanation of Solution
Antagonistic muscles are the group of muscles that move bones in the opposite direction. This is because the muscle contraction can pull the bone, but it can not push the bone away. The antagonistic group of muscles consists of flexor and extensor pair of muscle.
Some of the antagonistic muscle groups are as follows:
- Biceps and triceps muscle.
- Hamstring and quadriceps muscles.
- Tibialis anterior and gastrocnemius muscles.
Thus, biceps and triceps muscle; hamstring and quadriceps muscles; and tibialis anterior and gastrocnemius muscles are some of the antagonistic muscles present in a body.

To determine: The location of flexor and extensor muscles in antagonistic muscle groups.
Introduction: Flexor muscles bring the bones close together after contraction. This movement of contraction of flexor muscles is called flexion. On the other hand, extensor muscles move away the bone from each other after contraction. The movement of contraction of extensor muscles is called extension.
Explanation of Solution
Some of the antagonistic muscle groups with their location are as follows:
- Biceps and triceps muscle present in the upper arm. Biceps are flexor muscles, whereas triceps are extensor muscles.
- Hamstring and quadriceps muscles present in the upper leg in which hamstring are flexor muscles and quadriceps are extensor muscles.
- Tibialis anterior and gastrocnemius muscles are present in the ankle for the foot movement. Tibialis anterior is the flexor muscle, whereas gastrocnemius is the extensor muscles.
Thus, biceps, hamstring and tibialis anterior are the flexor muscles whereas triceps, quadriceps and gastrocnemius are the extensor muscles.
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Chapter 12 Solutions
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