title: Stiff muscle fibers in calf muscles of patients with cerebral palsy lead to high passive muscle stiffness.
abstract: Cerebral palsy (CP), caused by an injury to the developing brain, can lead to alterations in muscle function. Subsequently, increased muscle stiffness and decreased joint range of motion are often seen in patients with CP. We examined mechanical and biochemical properties of the gastrocnemius and soleus muscles, which are involved in equinus muscle contracture. Passive mechanical testing of single muscle fibers from gastrocnemius and soleus muscle of patients with CP undergoing surgery for equinus deformity showed a significant increase in fiber stiffness (p<0.01). Bundles of fibers that included their surrounding connective tissues showed no stiffness difference (p=0.28).). When in vivo sarcomere lengths were measured and fiber and bundle stiffness compared at these lengths, both fibers and bundles of patients with CP were predicted to be much stiffer in vivo compared to typically developing (TD) individuals. Interestingly, differences in fiber and bundle stiffness were not explained by typical biochemical measures such as titin molecular weight (a giant protein thought to impact fiber stiffness) or collagen content (a proxy for extracellular matrix amount). We suggest that the passive mechanical properties of fibers and bundles are thus poorly understood.
authors.affiliation: Department of Bioengineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California, 92093-0412.
authors.forename: Margie A
authors.initials: MA
authors.lastname: Mathewson
authors.forename: Henry G
authors.initials: HG
authors.lastname: Chambers
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Girard
authors.forename: Mayer
authors.initials: M
authors.lastname: Tenenhaus
authors.forename: Alexandra K
authors.initials: AK
authors.lastname: Schwartz
authors.forename: Richard L
authors.initials: RL
authors.lastname: Lieber
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D002547:Cerebral Palsy / Q000503:physiopathology*; D002648:Child; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000032:analysis; D012518:Sarcomeres / Q000502:physiology
chemical_list: D018995:Myosin Heavy Chains
keywords: cerebral palsy; human; mechanics; skeletal muscle