MUSCLE MECHANICS - Biomechanics and Motor Control of Human Movement - page 233

Figure 9.8 Contractile element producing maximum tension F c along with the tension
from F p from the parallel elastic element. Tendon tension is F i = F c + F p .

Figure 9.9 Tendon tension resulting from various levels of muscle activation. Par-
allel elastic element generates tension independent of the activation of the contractile
element.

under voluntary control. Thus, the overall force-length characteristics are a
function of the percentage of excitation, as seen in Figure 9.9.
The student can demonstrate the drop of tension at either end of the
force-length curve by two simple experiments. The hamstrings, as a two-joint
muscle, can be made to shorten as follows: the person stands on one leg, lean-
ing backward with the swing hip fully extended, then contracts the hamstrings
to flex the leg. He will feel the tension decrease drastically when the ham-
string muscles shorten before the knee is completely flexed. The converse
situation can be realized if the person attempts to extend the hip joint while
the knee is fully extended.

9.1.3 Series Elastic Tissue
All connective tissue in series with the contractile component, including the
tendon, is called the series elastic element . Under isometric contractions, it