Assessment of low-frequency fatigue with two methods of electrical stimulation.
The aim of this study was to compare the use of transcutaneous vs. motor nerve stimulation in the evaluation of low-frequency fatigue. Nine female and eleven male subjects, all physically active, performed a 30-min downhill run on a motorized treadmill. Knee extensor muscle contractile characteristics were measured before, immediately after (Post), and 30 min after the fatiguing exercise (Post30) by using single twitches and 0.5-s tetani at 20 Hz (P20) and 80 Hz (P80). The P20-to-P80 ratio was calculated. Electrical stimulations were randomly applied either maximally to the femoral nerve or via large surface electrodes (ES) at an intensity sufficient to evoke 50% of maximal voluntary contraction (MVC) during a 80-Hz tetanus. Voluntary activation level was also determined during isometric MVC by the twitch-interpolation technique. Knee extensor MVC and voluntary activation level decreased at all points in time postexercise (P < 0.001). P20 and P80 displayed significant time x gender x stimulation method interactions (P < 0.05 and P < 0.001, respectively). Both stimulation methods detected significant torque reductions at Post and Post30. Overall, ES tended to detect a greater impairment at Post in male and a lesser one in female subjects at both Post and Post30. Interestingly, the P20-P80 ratio relative decrease did not differ between the two methods of stimulation. The low-to-high frequency ratio only demonstrated a significant time effect (P < 0.001). It can be concluded that low-frequency fatigue due to eccentric exercise appears to be accurately assessable by ES.
Martin
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INSERM/ERIT-M 0207 Motricite-Plasticite Laboratory, Faculty of Sports Sciences-Univ. of Bourgogne, BP 27877, 21078 Dijon Cedex, France. vincent.martin@u-bourgogne.fr
Millet
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Martin
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Deley
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Lattier
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D000328:Adult; D004566:Electrodes; D004568:Electrodiagnosis / Q000379:methods*; D005221:Fatigue / Q000175:diagnosis* / Q000209:etiology; D005260:Female; D005267:Femoral Nerve / Q000503:physiopathology; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D010146:Pain / Q000209:etiology / Q000503:physiopathology; D012420:Running; D012727:Sex Characteristics; D012867:Skin; D012885:Skinfold Thickness