title: Effects of muscle activation on shear between human soleus and gastrocnemius muscles.
abstract: Lateral connections between muscles provide pathways for myofascial force transmission. To elucidate whether these pathways have functional roles in vivo, we examined whether activation could alter the shear between the soleus (SOL) and lateral gastrocnemius (LG) muscles. We hypothesized that selective activation of LG would decrease the stretch-induced shear between LG and SOL. Eleven volunteers underwent a series of knee joint manipulations where plantar flexion force, LG, and SOL muscle fascicle lengths and relative displacement of aponeuroses between the muscles were obtained. Data during a passive full range of motion were recorded, followed by 20° knee extension stretches in both passive conditions and with selective electrical stimulation of LG. During active stretch, plantar flexion force was 22% greater (P < 0.05) and relative displacement of aponeuroses was smaller than during passive stretch (P < 0.05). Soleus fascicle length changes did not differ between passive and active stretches but LG fascicles stretched less in the active than passive condition when the stretch began at angles of 70° and 90° of knee flexion (P < 0.05). The activity-induced decrease in the relative displacement of SOL and LG suggests stronger (stiffer) connectivity between the two muscles, at least at flexed knee joint angles, which may serve to facilitate myofascial force transmission.
authors.affiliation: Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyvaskyla, Jyvaskyla, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Finni
authors.affiliation: Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyvaskyla, Jyvaskyla, Finland.
authors.forename: N J
authors.initials: NJ
authors.lastname: Cronin
authors.affiliation: Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Mayfield
authors.affiliation: Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia.
authors.forename: G A
authors.initials: GA
authors.lastname: Lichtwark
authors.affiliation: Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia.
authors.forename: A G
authors.initials: AG
authors.lastname: Cresswell
mesh_terms: D000328:Adult; D000070606:Aponeurosis / Q000502:physiology; D001696:Biomechanical Phenomena; D064368:Healthy Volunteers; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D033081:Shear Strength / Q000502:physiology*; D055815:Young Adult
keywords: Myofascial force transmission; activation-dependent; aponeurosis; muscle contraction; muscle stretch; shear strain; tendon