Which one of the following produces weak actin-myosin bonding?
A. Active muscle contraction
B. Muscle immobility
C. Physiologic contracture
D. Active contraction in lengthened muscles
E. Reflexive muscle contraction
ANS: B
Rationale: When skeletal muscle is at rest, a small number of myosin crossbridges bind to actin but the crossbridge heads do not swivel. The longer muscle is immobile, the greater the number of actin-myosin weak bonds and the greater the muscle resistance to stretch. The hamstring stiffness upon standing after prolonged sitting is due to weak actin-myosin bonds.
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