title: Correlation between stiffness and electromechanical delay components during muscle contraction and relaxation before and after static stretching.
abstract: The study was aimed at assessing possible correlations of the electromechanical delay components during muscle contraction (DelayTOT) and relaxation (R-DelayTOT), with muscle-tendon unit (MTU), muscle, and tendon stiffness before and after static stretching (SS). Plantarflexor muscles' maximum voluntary torque (Tmax) was measured in 18 male participants (age 24±3yrs; body mass 76.4±8.9kg; stature 1.78±0.09m; mean±SD). During Tmax, surface electromyogram (EMG), mechanomyogram, and force signals were detected. DelayTOTand R-DelayTOTwith their electrochemical and mechanical components were calculated. Passive torque and myotendinous junction displacement were assessed at 0°, 10° and 20° of dorsiflexion to determine MTU, muscle and tendon stiffness. The same protocol was repeated after SS. DelayTOT, R-DelayTOTand their mainly mechanical components correlated with MTU, muscle and tendon stiffness, both before (R2from 0.562 to 0.894; p<0.001) and after SS (R2from 0.726 to 0.955; p<0.001). SS decreased Tmax(-14%; p<0.001) and lengthened almost all the DelayTOTand R-DelayTOTcomponents (from +5.9% to +30.5%; p<0.05). Correlations were found only between stiffness and the mechanical components of DelayTOTand R-DelayTOT. Correlations persisted after SS but delays increased to a higher extent than stiffness, indicating a complexity of the relationship between stiffness and delays that will be discussed in the manuscript.
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), University of Milan, Via G. Colombo 71, 20133 Milan, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Longo
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), University of Milan, Via G. Colombo 71, 20133 Milan, Italy.
authors.forename: Emiliano
authors.initials: E
authors.lastname: Cè
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), University of Milan, Via G. Colombo 71, 20133 Milan, Italy.
authors.forename: Susanna
authors.initials: S
authors.lastname: Rampichini
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), University of Milan, Via G. Colombo 71, 20133 Milan, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Devoto
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), University of Milan, Via G. Colombo 71, 20133 Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Venturelli
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), University of Milan, Via G. Colombo 71, 20133 Milan, Italy.
authors.forename: Eloisa
authors.initials: E
authors.lastname: Limonta
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), University of Milan, Via G. Colombo 71, 20133 Milan, Italy. Electronic address: fabio.esposito@unimi.it.
authors.forename: Fabio
authors.initials: F
authors.lastname: Esposito
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D009126:Muscle Relaxation; D052580:Muscle Stretching Exercises; D018482:Muscle, Skeletal / Q000502:physiology*; D011930:Reaction Time; D013710:Tendons / Q000502:physiology; D019415:Torque
keywords: Electromyogram; Mechanomyogram; Muscle stretch; Muscle-tendon unit; Ultrasound