Slowness of Onset of Contraction and Relaxation of the Total Smooth Muscle Tissue. A typical smooth muscle tissue begins to contract 50 to
100 milliseconds after it is excited, reaches full contraction about 0.5 second later,and then declines in
contractile force in another 1 to 2 seconds, giving a total contraction time of 1 to 3 seconds.
Maximum Force of Contraction Is Often Greater in Smooth Muscle Than in Skeletal Muscle. Despite the relatively few myosin filaments in
smooth muscle, and despite the slow cycling time of the cross-bridges, the maximum force of
contraction of smooth muscle is often greater than that of skeletal muscle—as great as 4 to 6 kg/ cm2
cross-sectional area for smooth muscle, in comparison with 3 to 4 kilograms for skeletal muscle. This
great force of smooth muscle contraction results from the prolonged period of attachment of the
myosin cross-bridges to the actin filaments.
