title: Quadriceps muscle use in the flywheel and barbell squat.
abstract: BACKGROUND
  Resistance exercise has been proposed as an aid to counteract quadriceps muscle atrophy in astronauts during extended missions in orbit. While space authorities have advocated the squat exercise should be prescribed, no exercise system suitable for in-flight use has been validated with regard to quadriceps muscle use. We compared muscle involvement in the terrestrial "gold standard" squat using free weights and a nongravity dependent flywheel resistance exercise device designed for use in space.
  
  
  METHODS
  The subjects were 10 strength-trained men who performed 5 sets of 10 repetitions using the barbell squat (BS; 10 repetition maximum) or flywheel squat (FS; each repetition maximal), respectively. Functional magnetic resonance imaging (MRI) and surface electromyography (EMG) techniques assessed quadriceps muscle use. Exercise-induced contrast shift of MR images was measured by means of transverse relaxation time (T2). EMG root mean square (RMS) was measured during concentric (CON) and eccentric (ECC) actions and normalized to EMG RMS determined during maximal voluntary contraction.
  
  
  RESULTS
  The quadriceps muscle group showed greater exercise-induced T2 increase following FS compared with BS. Among individual muscles, the rectus femoris displayed greater T2 increase with FS (+24 +/- 14%) than BS (+8 +/- 4%). Normalized quadriceps EMG showed no difference across exercise modes.
  
  
  CONCLUSIONS
  Collectively, the results of this study suggest that quadriceps muscle use in the squat is comparable, if not greater, with flywheel compared with free weight resistance exercise. Data appear to provide support for use of flywheel squat resistance exercise as a countermeasures adjunct during spaceflight.
authors.affiliation: Karolinska Institutet, Department of Physiology and Pharmacology, Stockholm, Sweden. lena.norrbrand@ki.se
authors.forename: Lena
authors.initials: L
authors.lastname: Norrbrand
authors.forename: Julio
authors.initials: J
authors.lastname: Tous-Fajardo
authors.forename: Roberto
authors.initials: R
authors.lastname: Vargas
authors.forename: Per A
authors.initials: PA
authors.lastname: Tesch
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology*; D055070:Resistance Training / Q000379:methods*