Fig. 2.

Rabbit psoas myofibril comprised of six sarcomeres that is stretched while activated from an average sarcomere length of about 2.4 μm to about 3.0 μm. After active stretching, all individual sarcomeres are on the descending limb of the force–length relationship, but there is no apparent overstretching or popping (quick sarcomere elongations beyond actin–myosin filament overlap: 3.9 μm) as has been proposed by proponents of the sarcomere length non-uniformity theory. Rather, sarcomeres seem to remain at an essentially constant length following the active stretch