title: The reproducibility of different metabolic markers for muscle fiber type distributions investigated by functional31P-MRS during dynamic exercise.
abstract: OBJECTIVE
  The objective of the study was to investigate the reproducibility of exercise induced pH-heterogeneity by splitting of the inorganic phosphate (Pi) signal in the corresponding31P-MRS spectra and to compare results of this approach with other fiber-type related markers, like phosphocreatine/adenosine triphosphate (PCr/ATP) ratio, and PCr-recovery parameters.
  
  
  METHODS
  Subjects (N=3) with different sportive background were tested in 10 test sessions separated by at least 3 days. A MR-compatible pedal ergometer was used to perform the exercise and to induce a pH-based splitting of the Pi-signal in31P-MR spectra of the medial gastrocnemius muscle. The PCr recovery was analyzed using a non-negative least square algorithm (NNLS) and multi-exponential regression analysis to estimate the number of non-exponential components as well as their amplitude and time constant. The reproducibility of the estimated metabolic marker and the resulting fiber-type distributions between the 10 test sessions were compared.
  
  
  RESULTS
  The reproducibility (standard deviation between measurements) based on (1) Pi components varied from 2% to 4%, (2) PCr recovery time components varied from 10% to 12% and (3) phosphate concentrations at rest varied from 8% to 11% between test sessions. Due to the sportive activity differences between the 3 subjects were expected in view of fiber type distribution. All estimated markers indicate the highest type I percentage for volunteer 3 medium for volunteer 2 and the lowest for volunteer 1.
  
  
  CONCLUSIONS
  The relative high reproducibility of pH dependent Pi components during exercise indicates a high potential of this method to estimate muscle fiber-type distributions in vivo. To make this method usable not only to detect differences in muscle fiber distributions but also to determine individual fiber-type volume contents it is therefore recommended to validate this marker by histological methods and to reveal the effects of muscle fiber recruitments and fiber-type specific Pi concentrations on the intensity ratios between the splitted Pi-components.
authors.affiliation: Medical Physics Group, Institute of Diagnostic and Interventional Radiology, University Hospital Jena, Germany. Electronic address: Reinhard.Rzanny@med.uni-jena.de.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Rzanny
authors.affiliation: Exercise Science, Institute of Sport and Movement Science, University of Stuttgart, Germany.
authors.forename: Norman
authors.initials: N
authors.lastname: Stutzig
authors.affiliation: Medical Physics Group, Institute of Diagnostic and Interventional Radiology, University Hospital Jena, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Hiepe
authors.affiliation: Medical Physics Group, Institute of Diagnostic and Interventional Radiology, University Hospital Jena, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Gussew
authors.affiliation: Exercise Science, Institute of Sports Science, Friedrich-Schiller-University Jena, Germany.
authors.forename: Hans-Alexander
authors.initials: HA
authors.lastname: Thorhauer
authors.affiliation: Medical Physics Group, Institute of Diagnostic and Interventional Radiology, University Hospital Jena, Germany.
authors.forename: Jürgen R
authors.initials: JR
authors.lastname: Reichenbach
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008657:Metabolic Clearance Rate; D057054:Molecular Imaging / Q000379:methods; D018485:Muscle Fibers, Skeletal / Q000145:classification* / Q000166:cytology / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism*; D017553:Phosphorus Compounds / Q000378:metabolism*; D010759:Phosphorus Isotopes / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D017553:Phosphorus Compounds; D010759:Phosphorus Isotopes; D019275:Radiopharmaceuticals; D010725:Phosphocreatine
keywords: (31)P-MR Spektroskopie; (31)P-MR spectroscopy; Dynamisches Pedalergometer; M. gastrocnemius; Muskelfaserverteilung; Muskelspektroskopie; dynamic load-pedal-ergometer; muscle fiber distribution; muscle spectroscopy