title: History-dependent force, angular velocity and muscular endurance in ACTN3 genotypes.
abstract: OBJECTIVE
  This study aimed at determining the influence of the ACTN3 R577X polymorphism on muscle strength and muscle endurance in non-athletic young men.
  
  
  METHODS
  266 healthy young men were included in this study. Each subject performed maximal isometric, concentric and eccentric contractions of the knee extensor muscles on an isokinetic dynamometer. Force depression, force enhancement and the fatigue index were derived from these data. In addition, handgrip strength, squat jump (SJ) and counter movement jump (CMJ) height were obtained.
  
  
  RESULTS
  Our group included 83 RR (31 %), 131 RX (49 %) and 52 XX (20 %) individuals. The muscle bone cross-sectional area of the thigh was 5 % higher in RR compared to XX individuals (P = 0.033). RR genotypes showed 6 % higher handgrip strength compared to the XX group (P = 0.047). They also jumped 5 % higher in both the SJ and CMJ tests (P = 0.029; P = 0.031). No differences were found in force depression, force enhancement, isometric or eccentric strength. The relative concentric knee torque at 200°/s and at 300°/s was 7 and 8 % higher in RR compared to XX genotypes, respectively (P = 0.049; P = 0.048). Also, the fatigue index was found to be 4 % lower in XX genotypes (P = 0.037).
  
  
  CONCLUSIONS
  Our findings are in agreement with the higher prevalence of the RR genotype in power-oriented activities. The better fatigue index of XX genotypes may be beneficial in endurance-type activities.
authors.affiliation: Exercise Physiology Research Group, Department of Kinesiology, Faculty of Kinesiology and Rehabilitation Sciences, KU Leuven, Louvain, Belgium, siacia.broos@faber.kuleuven.be.
authors.forename: Siacia
authors.initials: S
authors.lastname: Broos
authors.forename: Marc
authors.initials: M
authors.lastname: Van Leemputte
authors.forename: Louise
authors.initials: L
authors.lastname: Deldicque
authors.forename: Martine A
authors.initials: MA
authors.lastname: Thomis
mesh_terms: D000185:Actinin / Q000235:genetics*; D019412:Anatomy, Cross-Sectional; D001823:Body Composition / Q000235:genetics; D004247:DNA / Q000235:genetics; D005838:Genotype; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018763:Muscle Fatigue; D053580:Muscle Strength / Q000235:genetics / Q000502:physiology; D053581:Muscle Strength Dynamometer; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D010807:Physical Endurance / Q000235:genetics* / Q000502:physiology; D011110:Polymorphism, Genetic / Q000235:genetics; D019415:Torque; D055815:Young Adult
chemical_list: C118456:ACTN3 protein, human; D000185:Actinin; D004247:DNA