Additional in-series compliance reduces muscle force summation and alters the time course of force relaxation during fixed-end contractions

Abstract

There are high mechanical demands placed on skeletal muscles in movements requiring rapid acceleration of the body or its limbs. Tendons are responsible for transmitting muscle forces, but, because of their elasticity, can manipulate the mechanics of the internal contractile apparatus. Shortening of the contractile apparatus against the stretch of tendon affects force generation according to known mechanical properties; however, the extent to which differences in tendon compliance alter force development in response to a burst of electrical impulses is unclear. To establish the influence of series compliance on force summation, we studied electrically evoked doublet contractions in the cane toad peroneus muscle in the presence and absence of a compliant artificial tendon. Additional series compliance reduced tetanic force by two-thirds, a finding predicted based on the force-length property of skeletal muscle. Doublet force and force-time integral expressed relative to the twitch were also reduced by additional series compliance. Active shortening over a larger range of the ascending limb of the force-length curve and at a higher velocity, leading to a progressive reduction in forcegenerating potential, could be responsible. Muscle-tendon interaction may also explain the accelerated time course of force relaxation in the presence of additional compliance. Our findings suggest that a compliant tendon limits force summation under constant-length conditions. However, high series compliance can be mechanically advantageous when a muscle-tendon unit is actively stretched, permitting muscle fibres to generate force almost isometrically, as shown during stretch-shorten cycles in locomotor activities. Restricting active shortening would likely favour rapid force development.

Optimal length, calcium sensitivity, and twitch characteristics of skeletal muscles from mdm mice with a deletion in N2A titin

“…Mdm muscles exhibited a longer electromechanical delay, decreased rate of force development, increased relaxation time, and decreased active stress. A decrease in series elastic stiffness by increased tendon length would be consistent with these results (Bahler et al, 1967;Mayfield et al, 2016). However, mdm muscle preparations in this study had little to no tendon, but do show an increase in endomysial and perimysial connective tissue (Lopez et al, 2008;Powers et al, 2017), and have altered elastic properties that are consistent with greater compliance of active muscle (Monroy et al, 2017).…”

Development and sexual dimorphism of the sonic system in three deep-sea neobythitine fishes and comparisons between upper mid and lower continental slope

“…An important question is the selective advantage and function of long tendons in the nutritionally dilute lower-slope environment. Tendon function in movement has been examined mostly in leg muscles in a variety of tetrapods -frogs, turkeys, kangaroos, wallabies and primates including humans (Alexander, 2002;Biewener and Baudinette, 1995;Lichtwark and Barclay, 2010;Vereecke and Channon, 2013;Sawicki et al, 2015;Mayfield et al, 2016). Leg movement generally involves muscle contractions over a range of 0.2-11 Hz (Alexander, 2002), which would result in a volume velocity too low to produce audible sound.…”

Reduced muscle contractile function in elite young soccer players after a short-congested fixture period

“…18 These improvements in performance are achieved with higher stiffness since stiffness has been suggested to lead to higher maximum force and a higher rate of force development. 19 The above is supported by several authors who have demonstrated that elite athletes of several sports have stiffer tendon and muscles than amateurs, 16,20,21 since their joints tend to move less (i.e. they are more stable), especially when they meet the ground when jumping and running.…”