title: Resistance training increases in vivo quadriceps femoris muscle specific tension in young men.
abstract: OBJECTIVE
  The present study investigated whether in vivo human quadriceps femoris (QF) muscle specific tension changed following strength training by systematically determining QF maximal force and physiological cross-sectional area (PCSA).
  
  
  METHODS
  Seventeen untrained men (20 +/- 2 years) performed high-intensity leg-extension training three times a week for 9 weeks. Maximum tendon force (F(t)) was calculated from maximum voluntary contraction (MVC) torque, corrected for agonist and antagonist muscle activation, and moment arm length (d(PT)) before and after training. QF PCSA was calculated as the sum of the four component muscle volumes, each divided by its fascicle length. Dividing F(t) by the sum of the component muscle PCSAs, each multiplied by the cosine of the respective fascicle pennation angle, provided QF specific tension.
  
  
  RESULTS
  MVC torque and QF activation increased by 31% (P < 0.01) and 3% (P < 0.05), respectively, but there was no change in antagonist co-activation or d(PT). Subsequently, F(t) increased by 27% (P < 0.01). QF volume increased by 6% but fascicle length did not change in any of the component muscles, leading to a 6% increase in QF PCSA (P < 0.05). Fascicle pennation angle increased by 5% (P < 0.01) but only in the vastus lateralis muscle. Consequently, QF specific tension increased by 20% (P < 0.01).
  
  
  CONCLUSIONS
  An increase in human muscle specific tension appears to be a real consequence of resistance training rather than being an artefact of measuring errors but the underlying cause of this phenomenon remains to be determined.
authors.affiliation: Faculty of Science and Engineering, Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, UK. r.m.erskine@mmu.ac.uk
authors.forename: R M
authors.initials: RM
authors.lastname: Erskine
authors.forename: D A
authors.initials: DA
authors.lastname: Jones
authors.forename: A G
authors.initials: AG
authors.lastname: Williams
authors.forename: C E
authors.initials: CE
authors.lastname: Stewart
authors.forename: H
authors.initials: H
authors.lastname: Degens
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000293:Adolescent; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009129:Muscle Tonus / Q000502:physiology*; D052097:Quadriceps Muscle / Q000033:anatomy & histology / Q000502:physiology*; D055070:Resistance Training; D019415:Torque; D055815:Young Adult