Article

OBJECTIVE: To investigate the effects of medium frequency burst-modulated
alternating current on the current amplitude necessary to produce maximally
tolerated electrically stimulated quadriceps femoris isometric knee extension
torque. DESIGN: Ten healthy volunteers participated in this study. Neuromuscular
electrical stimulation was applied to the quadriceps femoris at two different
carrier frequencies: 2500 and 5000 Hz. All subjects received both frequencies in
a random order. Maximum voluntary isometric contraction torque of knee extension
was measured. The current amplitude (in milliamperes) required to produce
maximally tolerated isometric contraction knee extension torque at both carrier
frequencies was recorded. RESULTS: The mean maximally tolerated isometric
contraction torque (in %maximum voluntary isometric contraction) was 37.6% (SD,
+/-20.9) for 2500 Hz and 37.2% (SD, +/-20.9) for 5000 Hz. These values were not
significantly different (P = 0.944). However, the mean current amplitude required
to produce maximally tolerated isometric contraction torque with 2500 Hz was 91.9
(SD, +/-23.1) mA and with 5000 Hz it was 167.4 (SD, +/-34.5) mA (P < 0.001).
CONCLUSIONS: A carrier frequency of 2500 Hz is nearly twice as efficient for
generating quadriceps femoris knee extension torque as one at 5000 Hz. Using
lower medium frequency burst-modulated alternating current carrier frequencies
will allow lower current amplitudes to be used to generate maximum-tolerated
contraction torque, and will limit the possibility of reaching the upper limits
of current amplitude on an electrotherapeutic device before reaching an
individual's maximum tolerable contraction torque.

Langue : ANGLAIS