**No change in length of anisotropic band**

During muscle contraction, there are specific changes that occur within the muscle fibers. These changes involve the interaction between the thick myosin filaments and thin actin filaments, resulting in the shortening or contraction of the muscle. However, these changes do not affect the length of the anisotropic band.

**Explanation:**

To understand why the anisotropic band does not change in length during muscle contraction, it is important to understand the structure of a muscle sarcomere. A sarcomere is the basic contractile unit of a muscle fiber and is composed of thick myosin filaments and thin actin filaments.

1. **No change in length of A band:**
The A band is the region in the sarcomere where the thick myosin filaments are located. During muscle contraction, the A band does not change in length. This is because the myosin filaments remain stationary while the actin filaments slide past them.

2. **Decrease in length of isotropic band:**
The isotropic band, also known as the I band, is the region in the sarcomere where actin filaments are not overlapped by myosin filaments. During muscle contraction, the I band decreases in length. This is due to the actin filaments sliding towards the center of the sarcomere, overlapping with the myosin filaments.

3. **No change in length of anisotropic band:**
The anisotropic band, also known as the H band, is the region in the sarcomere where only myosin filaments are present. During muscle contraction, the H band does not change in length. This is because the myosin filaments do not slide or change position. Instead, they remain stationary while the actin filaments slide towards the center of the sarcomere.

4. **Decrease in length of actin myofilaments:**
The actin myofilaments, which are composed of actin proteins, play a crucial role in muscle contraction. During muscle contraction, the actin myofilaments slide towards the center of the sarcomere, overlapping with the myosin filaments. This sliding action is powered by the interaction between the myosin heads and actin filaments, resulting in the shortening or contraction of the muscle.

In conclusion, during muscle contraction, the length of the anisotropic band (H band) remains unchanged, while the isotropic band (I band) decreases in length. Additionally, the actin myofilaments also decrease in length as they slide towards the center of the sarcomere.