title: Architectural, functional and molecular responses to concentric and eccentric loading in human skeletal muscle.
abstract: OBJECTIVE
  We investigated architectural, functional and molecular responses of human skeletal muscle to concentric (CON) or eccentric (ECC) resistance training (RT).
  
  
  METHODS
  Twelve young males performed 10 weeks of concentric (CON) or eccentric (ECC) resistance training (RT) (n = 6 CON, 6 ECC). An additional 14 males were recruited to evaluate acute muscle fascicle behaviour and molecular signalling in biopsies collected from vastus lateralis (VL) after 30 min of single bouts of CON or ECC exercise. VL volume was measured by magnetic resonance imaging. Muscle architecture (fascicle length, Lf; pennation angle, PA) was evaluated by ultrasonography. Muscle remodelling signals to CON or ECC loading [MAPK/AKT-mammalian target of rapamycin (mTOR) signalling] and inflammatory pathway (TNFαMurf-1-MAFbx) were evaluated by immunoblotting.
  
  
  RESULTS
  Despite the ~1.2-fold greater load of the ECC group, similar increases in muscle volume (+8% CON and +6% ECC) and in maximal voluntary isometric contraction (+9% CON and +11% ECC) were found after RT. However, increases in Lf were greater after ECC than CON (+12 vs. +5%) while increases in PA were greater in CON than ECC (+30 vs. +5%). Distinct architectural adaptations were associated with preferential growth in the distal regions of VL for ECC (+ECC +8% vs. +CON +2) and mid belly for CON (ECC +7 vs. CON +11%). While MAPK activation (p38MAPK, ERK1/2, p90RSK) was specific to ECC, neither mode affected AKT-mTOR or inflammatory signalling 30 min after exercise.
  
  
  CONCLUSIONS
  Muscle growth with CON and ECC RT occurs with different morphological adaptations reflecting distinct fibre fascicle behaviour and molecular responses.
authors.affiliation: School of Graduate Entry Medicine and Health, MRC-ARUK Centre of Excellence for Musculoskeletal Ageing Research, University of Nottingham, Derby, UK; School of Healthcare Science, Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, UK.
authors.forename: M V
authors.initials: MV
authors.lastname: Franchi
authors.forename: P J
authors.initials: PJ
authors.lastname: Atherton
authors.forename: N D
authors.initials: ND
authors.lastname: Reeves
authors.forename: M
authors.initials: M
authors.lastname: Flück
authors.forename: J
authors.initials: J
authors.lastname: Williams
authors.forename: W K
authors.initials: WK
authors.lastname: Mitchell
authors.forename: A
authors.initials: A
authors.lastname: Selby
authors.forename: R M
authors.initials: RM
authors.lastname: Beltran Valls
authors.forename: M V
authors.initials: MV
authors.lastname: Narici
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D004576:Electromyography; D006801:Humans; D015151:Immunoblotting; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000378:metabolism*; D055070:Resistance Training / Q000379:methods*; D055815:Young Adult; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases
keywords: eccentric/concentric loading; muscle remodelling; resistance training