Question

The force generated by a muscle fiber increases as the sarcomere shortens but decreases at very short sarcomere lengths. Explain this observation. (Hint: Recall that cell volume remains constant during muscle contraction.)

Short answer

The force generation by a muscle fiber decreases at very short sarcomere lengths due to insufficient sliding between the myofilaments.

Step-by-step solution

Muscle contraction

During muscle contraction, the thick and the thin filaments slide pass each other to generate force. In this period, the muscle cells become shorter. However, the cells also become thicker, and the total volume of the cells does not change.

Force generation at very short sarcomere lengths

When the sarcomere length is very short, the potential for further shortening of the sarcomere, in other words, further contraction of the muscle is reduced, as the muscle cell total volume remains constant. This leads to an insufficient sliding between the thick and thin filaments. Thus, very less force is generated at very short sarcomere lengths.