title: Extracellular matrix adaptation of tendon and skeletal muscle to exercise.
abstract: The extracellular matrix (ECM) of connective tissues enables linking to other tissues, and plays a key role in force transmission and tissue structure maintenance in tendons, ligaments, bone and muscle. ECM turnover is influenced by physical activity, and both collagen synthesis and metalloprotease activity increase with mechanical loading. This can be shown by determining propeptide and proteinase activity by microdialysis, as well as by verifying the incorporation of infused stable isotope amino acids in biopsies. Local tissue expression and release of growth factors for ECM such as IGF-1, TGF-beta and IL-6 is enhanced following exercise. For tendons, metabolic activity (e.g. detected by positron emission tomography scanning), circulatory responses (e.g. as measured by near-infrared spectroscopy and dye dilution) and collagen turnover are markedly increased after exercise. Tendon blood flow is regulated by cyclooxygenase-2 (COX-2)-mediated pathways, and glucose uptake is regulated by specific pathways in tendons that differ from those in skeletal muscle. Chronic loading in the form of physical training leads both to increased collagen turnover as well as to some degree of net collagen synthesis. These changes modify the mechanical properties and the viscoelastic characteristics of the tissue, decrease its stress-susceptibility and probably make it more load-resistant. The mechanical properties of tendon fascicles vary within a given human tendon, and even show gender differences. The latter is supported by findings of gender-related differences in the activation of collagen synthesis with exercise. These findings may provide the basis for understanding tissue overloading and injury in both tendons and skeletal muscle.
authors.affiliation: Institute of Sports Medicine, Bispebjerg Hospital, Copenhagen, Denmark. mk01@bbh.hosp.dk
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
authors.forename: Peter
authors.initials: P
authors.lastname: Magnusson
authors.forename: Michael
authors.initials: M
authors.lastname: Krogsgaard
authors.forename: Jens
authors.initials: J
authors.lastname: Boysen Møller
authors.forename: Jens
authors.initials: J
authors.lastname: Olesen
authors.forename: Katja
authors.initials: K
authors.lastname: Heinemeier
authors.forename: Mette
authors.initials: M
authors.lastname: Hansen
authors.forename: Bjarki
authors.initials: B
authors.lastname: Haraldsson
authors.forename: Satu
authors.initials: S
authors.lastname: Koskinen
authors.forename: Birgitte
authors.initials: B
authors.lastname: Esmarck
authors.forename: Henning
authors.initials: H
authors.lastname: Langberg
mesh_terms: D001842:Bone and Bones / Q000502:physiology; D003094:Collagen / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005109:Extracellular Matrix / Q000502:physiology*; D005260:Female; D006133:Growth Substances / Q000378:metabolism; D006801:Humans; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000502:physiology*; D010806:Physical Education and Training; D014176:Protein Biosynthesis / Q000502:physiology; D012737:Sex Factors; D013314:Stress, Mechanical; D013710:Tendons / Q000098:blood supply / Q000502:physiology*
chemical_list: D006133:Growth Substances; D009124:Muscle Proteins; D003094:Collagen