Residual force enhancement after stretch of contracting frog single muscle fibers.

Abstract

Single fibers from the tibialis anterior muscle of Rana temporaria at 0 .8-3 .8°C were subjected to long tetani lasting up to 8 s . Stretch of the fiber early in the tetanus caused an enhancement of force above the isometric control level which decayed only slowly and stayed higher throughout the contraction .This residual enhancement was uninfluenced by velocity of stretch and occurred only on the descending limb of the length-tension curve . The absolute magnitude of the effect increased with sarcomere length to a maximum at^-2 .9 ,um and then declined . The phenomenon was further characterized by its dependence on the amplitude of stretch . The final force level reached after stretch was usually higher than the isometric force level corresponding to the starting length of the stretch . The possibility that the phenomenon was caused by nonuniformity of sarcomere length along the fiber was examined by (a) laser diffraction studies that showed sarcomere stretch at all locations and (b) studies of 9-10 segment lengths of^-0 .6-0.7 mm along the entire fiber, which all elongated during stretch . Length-clamped segments showed residual force enhancement after stretch when compared with the tetanus produced by the same segment held at the short length as well as at the long length . It is concluded that residual force enhancement after stretch is a property shown by all individual segments along the fiber.

Is titin a ‘winding filament’? A new twist on muscle contraction

“…The results are qualitatively similar to experimental observations [63]. These results demonstrate that the winding filament hypothesis accounts for the observed pattern of residual force enhancement in actively stretched muscle.…”

“…(a) History dependence History-dependent changes in active force production include enhancement of force with stretch and depression of force with shortening [6,63,77]. The steady-state force produced by muscles after active shortening is less than the isometric force at a corresponding length, and likewise the steady-state force following active lengthening is higher than the isometric force at a corresponding length.…”

A continuum model for skeletal muscle contraction at homogeneous finite deformations

“…The model is confined to homogeneous strain fields and fully tetanized conditions to limit the complexity. Further, aspects such as pennation angle and residual force enhancement (McMahon 1984;Edman et al 1982) are also excluded herein.…”

Force produced by isolated sarcomeres and half-sarcomeres after an imposed stretch

“…It has been directly associated with several experimental observations, including the force "creep" observed at long muscle lengths (11,16), the relation between force and filament overlap (11,17,19), the kinetics of force development and relaxation (9,43), and the effects of muscle stretch in force production (7,8,13,18,36,37). The latest is particularly important: when a stretch is applied to skeletal muscles during activation, force increases significantly while the energy consumption decreases (1,30).…”

“…The latest is particularly important: when a stretch is applied to skeletal muscles during activation, force increases significantly while the energy consumption decreases (1,30). The force remains elevated after the stretch to reach a steady-state level that is higher than that produced during isometric contractions at corresponding lengths (8,24,38). The mechanisms responsible for this "residual force enhancement" remain elusive and there is substantial disagreement in the literature.…”