3: Figure 3.5 Animation Video
Transcript:
Muscular Contractions
Three types of contractions can occur in muscles—isometric, concentric, and eccentric contractions. Let's look at the biceps and the triceps muscle groups of the upper arm to see examples of the three different types of contractions. Initially we see an example of isometric contraction. Both the biceps and the triceps develop tension, but there is no movement and neither muscle group changes length.
As the weight is lifted up, concentric contraction occurs in the biceps. The biceps—acting as the agonist muscle group—contracts, while the triceps—the antagonist muscle group—relaxes.
When the weight is lowered to the person's side, the arm is extended, and eccentric contraction occurs in the biceps. Notice here that the biceps lengthens as it experiences eccentric contraction. Here, the biceps is providing a braking force so that the weight does not fall unchecked. The triceps remains relaxed.
Let's review. Lifting the weight up causes concentric contraction in the biceps. The biceps contract and the triceps relax. Lowering the weight and extending the arm causes the biceps to lengthen as it undergoes eccentric contraction. Isometric contractions occur when holding the weight in place with no shortening or lengthening of the muscles.