title: Calcium sensitivity of human single muscle fibers following plyometric training.
abstract: OBJECTIVE
  To study the effect of plyometric training on Ca2+ sensitivity and the influence of troponin T (TnT) isoforms on Ca2+ -activation properties in skinned human muscle fibers.
  
  
  METHODS
  Biopsies were obtained from the vastus lateralis of eight men before and after the training period. Chemically skinned fibers were evaluated regarding their Ca2+ -activation properties and were classified according to their myosin heavy chain (MHC) contents and analyzed regarding their slow and fast TnT isoforms.
  
  
  RESULTS
  After training, significant improvements (P < 0.05) were found for static jump, countermovement jump, 6 x 5-m shuttle-run test, and leg-press performances. An 8% increase in the proportion of type IIa fibers (P < 0.05) was observed. Single-fiber diameters increased by 11% in type I (P < 0.01), 10% in type IIa (P < 0.001), and 15% in type IIa/IIx fibers (P < 0.001). Peak fiber force increased by 35% in type I (P < 0.001), 25% in type IIa (P < 0.001), and 57% in type IIa/IIx fibers (P < 0.01). The Ca2+ -activation threshold was not altered by training, but the Ca2+ concentration required to elicit half-maximal activation showed a decreasing trend, with significant changes in type I fibers (P < 0.001). Cooperativity at low Ca2+ concentrations was increased in type I and type IIa/IIx fibers (P < 0.05). Type I fibers exclusively expressed slow TnT isoforms, and type II fibers were always associated with fast TnT isoforms, independent of training status. Therefore, changes in Ca2+ sensitivity after training could not be explained by differential fast or slow TnT isoform expression.
  
  
  CONCLUSIONS
  Plyometric training increased single-fiber Ca2+ sensitivity, especially in type I fibers. These changes could not be explained by a modified TnT isoform expression pattern.
authors.affiliation: Department of Physical Education and Rehabilitation, Faculty of Medicine, Catholic University of Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Laurent
authors.initials: L
authors.lastname: Malisoux
authors.forename: Marc
authors.initials: M
authors.lastname: Francaux
authors.forename: Henri
authors.initials: H
authors.lastname: Nielens
authors.forename: Patricia
authors.initials: P
authors.lastname: Renard
authors.forename: Jean
authors.initials: J
authors.lastname: Lebacq
authors.forename: Daniel
authors.initials: D
authors.lastname: Theisen
mesh_terms: D000328:Adult; D001707:Biopsy, Needle; D002118:Calcium / Q000378:metabolism*; D006801:Humans; D007866:Leg; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000473:pathology; D018482:Muscle, Skeletal / Q000473:pathology; D010806:Physical Education and Training / Q000379:methods*; D020033:Protein Isoforms / Q000378:metabolism; D020107:Troponin T / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D020107:Troponin T; D002118:Calcium