A 10 mus component in the tension transients of isolated intact skeletal muscle fibres of the frog.

The transients of the tension and the angle of a first order diffraction line of isolated single intact muscle fibres of the M. lumbricalis IV of the foot resulting from rapid length changes have been measured. Furthermore simulations of the tension transients, taking the resonance frequency of the force transducer, the inertia of the fibre and the influence of the surrounding fluid into account, are presented. The tension transients could be simulated by a system of continuous elements with undamped elasticity - Young's modulus E1 = 1.8 X 10(8) N/m2 - in series with elasticity E2 = 5.4 X 10(7) N/m2 parallel to a damping element - coefficient of damping mu = 2,300 Ns/m2; yielding a relaxation time of 10 mus. The Young's modulus of the undamped series elasticity E1 implies that a sudden shortening of 2 nm per half sarcomere should reduce the active tension to zero. The results obtained from the diffraction pattern recording show that the displacement in the fibre is in accordance with the relative length change caused by the displacement generator. It is therefore believed that the tendon and tendon-muscle junction are sufficiently stiff to allow ascribing the above-mentioned elasticity and damping to the fibre itself.