Answer
The forcefulness of a muscle contraction depends on the length of the sarcomeres before the contraction begins.. Given a sarcomere length close to that of resting length, of most sarcomeres--2.0-2.4 um--the zone of overlap between thin and thick filaments will be optimal; therefore, the sarcomere will develop maximal force/tension on contraction. In such cases, the zone of overlap between thick and thin filaments extends from edge of the H zone to the end of the thick filaments.
If the sarcomeres of a muscle fiber are stretched beyond resting length, the zone of overlap shortens and fewer myosin heads can make contact with thin (actin) filaments. As a consequence, the muscle fiber generates less tension. However, if the sarcomeres are stretched beyond optimal length--say about 170% of resting length--there will be no overlap between thin and thick filaments and the muscle cannot contract and generate tension. In addition, if the sarcomere lengths get progressively shorter than optimal, the tension generalble decreases. This is so because the filaments fold or scrunch as they are compressed by the Z disc, and fewer myosin heads can make contact with thin actin filaments.
Work Step by Step
Normally, sarcomeres in resting muscles are close to resting length. They transmit force and cause movement by their attachment to bones and other inelastic tissues.
