Stiffness changes in frog skeletal muscle during contraction recorded using ultrasonic waves.

Abstract

SUMMARY1. A technique has been developed with which the stiffness changes in frog skeletal muscle can be continuously recorded by measuring the propagation velocity of ultrasonic waves (3-7 MHz) with negligibly small perturbations to the contractile system.2. The resting muscle stiffness was 2 256+00002 x 109 N/m2 (S.D.) at 1-2°C (n = 10) and 2-480+0-007 x 109 N/M2 at 19-20°C (n = 12) in the longitudinal direction, and 2-223 + 04008 x 109 N/m2 at 1-2°C (n = 8) and 2 437 + 0 007 x 109 N/M2 at 19-20°C (n = 9) in the transverse direction.3. The resting muscle stiffness measured with ultrasonic waves was virtually insensitive to the resting force development, i.e. the extension of the parallel elastic component.4. The longitudinal muscle stiffness increased during isometric contraction at a rate faster than the force development. The amount of increase of the longitudinal stiffness in an isometric tetanus at 2 2 ,um sarcomere length was 24 ±+01 x 107 N/M2 at 1-2°C (n = 10) and 6-5 + 1-3 x 107 N/m2 at 19-20°C (n = 12).5. On the other hand, the transverse muscle stiffness decreased during isometric contraction at a rate faster than the force development. The amount of decrease of the transverse stiffness in an isometric tetanus at 22 jtm sarcomere length was 5-6+01 x 107 N/M2 at 1-2°C (n = 8) and 64+0-3 x 107 N/M2 at 19-20°C (n = 9).6. The amount of both the longitudinal and the transverse stiffness changes during an isometric tetanus decreased linearly with increasing sarcomere length, indicating that the stiffness changes during contraction reflect the formation of cross-links between the myofilaments.7. Both the longitudinal and the transverse stiffness increased when resting muscle was put into rigor state. The rigor muscle stiffness was insensitive to small stretches, i.e. the strain of the rigor cross-links.8. These results are discussed in connection with the behaviour of cross-bridges during isometric contraction and in rigor.

Effects of intracellular acidification and varied temperature on force, stiffness, and speed of shortening in frog muscle fibers

“…In accordance with previous observations at low temperature in frog muscle (3,8,20,26,29), Fig. 1, C and D, demonstrates that stiffness was in the lead of tension during the rising phase of the tetanus, and this applies to both low and high temperatures.…”

Shortening of muscle fibres during stretch of the active cat medial gastrocnemius muscle: the role of tendon compliance.

“…7 C). When the muscle was starting to stretch, the muscle fibre lengths were about 17 mm in this cat and correction for changes of sound velocity of 1-3 % (Hatta et al 1988) results in an estimated true shortening of 1-0 + 0 3 mm with a range of 0 1-1P9 mm. Walking speed varied from 0 3-0 5 m s-1.…”

“…The ultrasound method assumes a constant velocity of sound in the muscle throughout the contraction. Since the stiffness of the muscle increases during contraction, the speed of sound will also increase in the order of 1-3 % (Hatta, Sugi & Tamura, 1988). Therefore a recorded shortening of 1-3% may be due only to the increase in sound velocity.…”

Mechano-chemical model describing the force-velocity relationship in muscle

“…It is important that eq. [4] is a necessary condition in order that eq. [3] can simulate the hyperbolic force-velocity relationship in muscle, unless the plastic deformation does not occur.…”

“…It is mathematically identical with Hill's equation, but comprises a single dimensionless constant, "~3", which determines the [1] and eqs. [3], [4]. Ordinate indicates the rate of the release of energy of muscle and abscissa the load.…”