Strategies that improve paralyzed human quadriceps femoris muscle performance during repetitive, nonisometric contractions.
OBJECTIVE
To determine the effect of combining different stimulation frequencies on the ability of paralyzed human quadriceps muscle to produce a 50 degrees knee excursion repetitively when starting at 90 degrees of flexion.


METHODS
Repeated-measures design.


METHODS
Clinical research laboratory.


METHODS
Complete data were collected from 9 subjects aged 11 to 25 years (mean +/- standard deviation, 17.1+/-4.5y) with spinal cord injury (SCI).


METHODS
Three protocols were each tested during separate sessions: 20-Hz trains of pulses followed by 66-Hz trains (C20+66), 33-Hz trains followed by 66-Hz trains (C33+66), and 66-Hz trains alone (C66). For each frequency, stimulation was repeated until the knee failed to produce a 50 degrees excursion. This approach allowed us to evaluate the response to stimulation with 20-, 33-, and 66-Hz and combinations of 20- and 66-Hz and 33- and 66-Hz trains.


METHODS
Number of successful contractions.


RESULTS
The C20 and C33 did not differ (mean, 41.0+/-12.6 excursions and 42.0+/-12.3 excursions, respectively), and each produced more excursions than the C66 protocol. The C20+66 and C33+66 protocols produced 51.4+/-15.0 and 44.9+/-13.6 excursions, respectively, and the C20+66 was the best protocol overall (all P<or=.05).


CONCLUSIONS
This study showed that stimulation strategies that start with low frequencies and switch to higher frequencies as the muscle fatigues could improve the ability of functional electric stimulation applications to perform repetitive, nonisometric contractions in subjects with SCI.
Kebaetse
Maikutlo B
MB
Graduate Program in Biomechanics, University of Delaware, Newark, DE 19716, USA.
Lee
Samuel C
SC
Johnston
Therese E
TE
Binder-Macleod
Stuart A
SA
D000328:Adult; D002574:Cervical Vertebrae; D002648:Child; D004558:Electric Stimulation / Q000379:methods*; D005260:Female; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology*; D007717:Knee / Q000503:physiopathology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D010243:Paralysis / Q000209:etiology / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000150:complications / Q000503:physiopathology*; D013904:Thoracic Vertebrae