title: The effect of the oral contraceptive pill on the passive stiffness of the human gastrocnemius muscle in vivo.
abstract: The aim of this investigation was to determine the effect of sustained monophasic oral contraceptive pill (MOCP) use on the in vivo passive stiffness of the gastrocnemius medialis (GM) muscle-tendon unit. Twenty four females volunteered for this study (age range 20-25 yrs); twelve participants had been taking the combined MOCP for a minimum of 12 months, and twelve participants, who had never taken the MOCP, formed a control group. Distal displacement of the GM myotendinous junction (MTJ) was measured during passive dorsiflexion at 2 Nm increments to 20 Nm, and at end range of motion using ultrasonography. In addition, GM MTJ displacement was measured at passive torques equivalent to 5, 10 and 15% of plantarflexion maximal voluntary contraction (MVC) torque, and relative to GM length. MOCP users had significantly greater GM MTJ displacement at all passive torques (P<0.01), reaching 40% more at 20 Nm; these displacements remained significantly different when MVC and GM length were accounted for (P<0.01). Passive muscle stiffness from 0-20 Nm was 31% less in MOCP users compared to non-users (P<0.01). In conclusion, based on the in vivo assessment of GM MTJ displacement, passive muscle stiffness is less in MOCP using females, compared to non-pill users.
authors: Institute for Performance Research, Department of Exercise and Sport Science, Manchester Metropolitan University Cheshire, United Kingdom. c.morse@mmu.ac.uk
authors: C I
authors: CI
authors: Morse
authors: J
authors: J
authors: Spencer
authors: A W
authors: AW
authors: Hussain
authors: G L
authors: GL
authors: Onambele
mesh_terms: D000328:Adult; D003276:Contraceptives, Oral / Q000008:administration & dosage / Q000009:adverse effects*; D005260:Female; D006801:Humans; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000187:drug effects* / Q000502:physiology; D016059:Range of Motion, Articular / Q000187:drug effects* / Q000502:physiology; D013710:Tendons / Q000000981:diagnostic imaging* / Q000187:drug effects* / Q000502:physiology; D014463:Ultrasonography; D055815:Young Adult
chemical_list: D003276:Contraceptives, Oral