Quadriceps strength and fatigue assessed by magnetic stimulation of the femoral nerve in man

Abstract

There is no nonvolitional method of assessing quadriceps strength which both supramaximally activates the muscle and is acceptable to subjects. In 10 normal subjects and 10 patients with suspected muscle weakness we used magnetic stimulation of the femoral nerve to elicit an isometric twitch and measured twitch tension (TwQ), surface electromyogram in addition to the maximum voluntary contraction force (MVC). Supramaximality was achieved in all subjects at a mean of 83% of maximum stimulator output. When supramaximal, TwQ was reproducible (mean coefficient of variation 3.6%, range 0.7–10.9) and correlated well with MVC (r2 = 0.83, P < 0.001). In 7 normal subjects we measured TwQ before and after a fatiguing protocol; after 20 min TwQ was a mean of 55% (range 29–77%) of baseline and remained substantially reduced at 90 min. Magnetic femoral nerve stimulation is a painless, supramaximal method of assessing quadriceps strength and fatigue which is likely to be of value in clinical and physiological studies. © 1996 John Wiley & Sons, Inc.

Effect of exercise-induced arterial hypoxemia on quadriceps muscle fatigue in healthy humans

“…Care was taken to ensure that the knee angle did not change, the ankle strap and load cell were parallel to the floor, and the ankle strap position remained constant throughout the experiment. Two magnetic stimulators (Magstim 200; Jali Medical, Newton, MA), connected to a transformer (TwinCap module; Jali Medical) and a double 40-mm coil (D40-1183.00), were used to stimulate the femoral nerve (30,40). We used single and paired stimuli to help discriminate between low-and high-frequency fatigue (39,53).…”

“…The area of stimulation associated with the largest quadriceps twitch (Q tw) and M-wave amplitudes was located by positioning the coil head high in the femoral triangle just lateral to the femoral artery (40). This position was marked with indelible ink to ensure that the coil was placed at the same location for the remainder of the study.…”

“…Accordingly, we measured quadriceps twitch force 5 s after a 5-s maximal voluntary contraction (MVC) of the quadriceps and repeated this procedure six times such that six Q tw,pot values were obtained. Like others (30,40), we found that the degree of potentiation was slightly smaller after the first and, to a lesser extent, after the second MVC; therefore, we discarded the first two measurements. Activation of the quadriceps during the MVC was assessed using a superimposed twitch technique (46).…”

Effects of acute fatigue on the volitional and magnetically-evoked electromechanical delay of the knee flexors in males and females

“…Protocols to elicit supra-maximal stimulation of the femoral nerve have been described briefly in the literature (Polkey et al 1996;Vivodtzev et al 2005). …”

“…Recent technological advances, however, have enabled the noninvasive and painless magnetic stimulation of a peripheral motor nerve; the efficacy of this technique has been considered in clinical populations where maximal volitional testing is not appropriate (Polkey et al 1996;Vivodtzev et al 2005). Peripheral magnetic stimulation of a nerve root offers the potential to activate the fastest motor units (King and Chippa 1989;Maertens de Noordhout 1991) and overcome factors associated with the volitional activation of muscle that might otherwise intrude on the proper estimation of an individual's true maximal performance capacity.…”