Effects of neuromuscular electrical stimulation parameters on specific tension

European Journal of Applied Physiology(2006)

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Abstract
This study examined the effects of altering surface neuromuscular electrical stimulation (SNMES) parameters on the specific tension of the quadriceps femoris muscle. Seven able-bodied subjects had magnetic resonance images taken of both thighs prior to and immediately after four SNMES protocols to determine the activated muscle cross-sectional area (CSA). The four protocols were: (1) research (RES, 100 Hz, 450 μs, and amplitude set to evoke 75% of maximal voluntary isometric torque, MVIT); (2) pulse duration (PD, 100 Hz, 150 μs, same current as in RES); (3) frequency (FREQ, 25 Hz, 450 μs, and same current as in RES); (4) amplitude (AMP, 100 Hz, 450 μs, and current set to evoke the average of the initial torques of PD and FREQ, 45 ± 9% of MVIT). Reducing the amplitude of the current from 75 to 45% of MVIT did not alter specific tension, 25 ± 8 N/cm 2 , suggesting that the amplitude probably affects torque and the area of activated muscle proportionally. Shortening the pulse duration from 450 to 150 μs caused specific tension to drop from 25 ± 6 to 20 ± 6 N/cm 2 ( P < 0.05), indicating that pulse duration increased torque and the activated CSA disproportionally. Alternatively, reducing the frequency from 100 to 25 Hz decreased specific tension from 25 ± 6 to 17 ± 4 N/cm 2 ( P < 0.05), suggesting that the frequency increased torque without affecting the activated CSA. Clinicians who administer SNMES should be aware of the magnitude of adaptations to a given amplitude, pulse duration, and frequency.
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Key words
electrical stimulation,amplitude,frequency,pulse duration,specific tension
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