title: Force reduction induced by unidirectional transversal muscle loading is independent of local pressure.
abstract: Transversal unidirectional compression applied to muscles via external loading affects muscle contraction dynamics in the longitudinal direction. A recent study reported decreasing longitudinal muscle forces with increasing transversal load applied with a constant contact area (i.e., leading to a simultaneous increase in local pressure). To shed light on these results, we examine whether the decrease in longitudinal force depends on the load, the local pressure, or both. To this end, we perform isometric experiments on rat M. gastrocnemius medialis without and with transversal loading (i) changing the local pressure from 1.1-3.2Ncm(-2) (n=9) at a constant transversal load (1.62N) and (ii) increasing the transversal load (1.15-3.45N) at a constant local pressure of 2.3Ncm(-2) (n=7). While we did not note changes in the decrease in longitudinal muscle force in the first experiment, the second experiment resulted in an almost-linear reduction of longitudinal force between 7.5±0.6% and 14.1±1.7%. We conclude that the observed longitudinal force reduction is not induced by local effects such as malfunction of single muscle compartments, but that similar internal stress conditions and myofilament configurations occur when the local pressure changes given a constant load. The decreased longitudinal force may be explained by increased internal pressure and a deformed myofilament lattice that is likely associated with the decomposition of cross-bridge forces on the one hand and the inhibition of cross-bridges on the other hand.
authors.affiliation: Institute of Sport and Motion Science, University of Stuttgart, Stuttgart, Germany. Electronic address: tobias.siebert@inspo.uni-stuttgart.de.
authors.forename: Tobias
authors.initials: T
authors.lastname: Siebert
authors.affiliation: Department of Motion Science, Friedrich-Schiller University Jena, Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Rode
authors.affiliation: Department of Motion Science, Friedrich-Schiller University Jena, Jena, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Till
authors.affiliation: Institute of Sport and Motion Science, University of Stuttgart, Stuttgart, Germany.
authors.forename: Norman
authors.initials: N
authors.lastname: Stutzig
authors.affiliation: Department of Motion Science, Friedrich-Schiller University Jena, Jena, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Blickhan
mesh_terms: D000818:Animals; D007537:Isometric Contraction / Q000502:physiology; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D011312:Pressure; D017208:Rats, Wistar; D013314:Stress, Mechanical
keywords: Impact load; Isometric contraction; Muscle compression; Rattus norvegicus; Viscoelastic material properties