Muscle Interactions: Pairing of the Biceps and Triceps
Skeletal muscles are voluntary muscles that are directly attached to the skeleton. These muscles work in pairs. In the upper arm, the biceps and triceps muscles work together to bend and straighten the elbow. When the biceps (on the front of upper arm) is contracted, or shortened, the triceps (on the back of upper arm) is elongated, or made longer, and the elbow bends. When the triceps is contracted, the biceps is elongated, and the elbow is straightened. Since neither muscle can stretch itself, it must be stretched by its partner, and for this reason these muscles are called antagonist (partner) muscles. In this activity you will see how the biceps and triceps muscles work together when pushing and pulling.
- Place one hand under the table so your palm is flat against the underside of the table. Keep your elbow bent. Use that hand to push upward on the table as if you were attempting to lift it. As you do this, use your other hand to feel the muscles being used in the upper arm. Feel both of the biceps and triceps muscles as you pull upward. Attempt to determine which one is being contracted and which one is being elongated.
- Next take that same hand and put it palm down on top of the table. Push downward on the table. Again, feel the muscles of that upper arm. Determine what the biceps and triceps are doing during this process.
- During which of the two activities did the biceps muscle feel harder? During which activity did the triceps muscle feel harder?
- Using the words contract and elongate, describe what the biceps and triceps muscles were doing during both of the activities performed today.
- The biceps muscle was harder when you were attempting to lift up on the desk. The triceps was harder when you pushed down on the top of the desk.
- Answers will vary, but students should point out that when the biceps are contracted, the triceps are elongated and vice versa.
Think of an activity you can do to see how the muscles of the upper leg (quadriceps and hamstrings) work in pairs. Perform the activity and describe what is happening.