title: Effects of low frequency functional electrical stimulation with 15 and 50 Hz on muscle strength in heart failure patients.
abstract: OBJECTIVE
  To compare the acute effects of functional electrical stimulation (FES) with 15 and 50 Hertz (Hz) frequencies on muscle strength in patients with heart failure with healthy individuals.
  
  
  METHODS
  Twenty-two 61.6 ± 1.0 y-old male volunteers were studied: 10 patients with heart failure (functional class II-III) and 12 healthy controls. The isometric muscle peak torque (IMPT) of the quadriceps femoral muscle was measured through a Biodex dynamometer in maximum voluntary contraction (MVC), and under FES of 50 Hz and 15 Hz, which was applied with a 0.4 ms pulse width, 10-s contraction time, 50-s resting time and maximum tolerable intensity.
  
  
  RESULTS
  The IMPT differed in MVC, 50 Hz and 15 Hz FES both in patients (201.9 ± 14, 55.6 ± 13 and 42.1 ± 12 Newton-metre, respectively; p < 0.001) and in controls (179.3 ± 9, 62.4 ± 8 and 52.3 ± 7 Newton-metre, respectively; p < 0.001). There were no differences between the groups. In patients and controls, respectively, the 50 Hz FES corresponded to 27% versus 35% and the 15 Hz to 21% versus 29% of the IMPT generated at the MVC (p < 0.001).
  
  
  CONCLUSIONS
  This result can be attributed to the fact that muscle strength is proportional to the stimulation frequency and to the number of recruited motor units. Thus, the higher the frequency, the greater the motor recruiting, producing increased muscle strength.
  
  
  CONCLUSIONS
  The IMPT generated by acute 50 Hz application of FES is higher than the one generated by 15 Hz, but it is lower than MVC in controls and patients with heart failure.
authors.affiliation: Institute of Cardiology of Rio Grande do Sul/University Foundation of Cardiology (IC/FUC), Clinical Research Laboratory, Porto Alegre, Brazil.
authors.forename: Graciele
authors.initials: G
authors.lastname: Sbruzzi
authors.forename: Beatriz D'agord
authors.initials: BD
authors.lastname: Schaan
authors.forename: Gilnei Lopes
authors.initials: GL
authors.lastname: Pimentel
authors.forename: Luis Ulisses
authors.initials: LU
authors.lastname: Signori
authors.forename: Ant Nio Marcos Vargas
authors.initials: AN
authors.lastname: Da Silva
authors.forename: Milton Seigui
authors.initials: MS
authors.lastname: Oshiro
authors.forename: Maria Claudia
authors.initials: MC
authors.lastname: Irigoyen
authors.forename: Rodrigo Della Méa
authors.initials: RD
authors.lastname: Plentz
mesh_terms: D000704:Analysis of Variance; D016022:Case-Control Studies; D004599:Electric Stimulation Therapy / Q000379:methods*; D006333:Heart Failure / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D018709:Statistics, Nonparametric; D019415:Torque; D016896:Treatment Outcome