HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 103/3/739    most recent 00025.2007v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Swallow, E. B. Articles by Polkey, M. I. Search for Related Content PubMed PubMed Citation Articles by Swallow, E. B. Articles by Polkey, M. I.

A novel technique for nonvolitional assessment of quadriceps muscle endurance in humans

¹Respiratory Muscle Laboratory, Royal Brompton Hospital, London, United Kingdom; ²Department of Respiratory Medicine, University of Maastricht, Maastricht, The Netherlands; and ³Respiratory Muscle Laboratory, King's College London School of Medicine, London, United Kingdom

Submitted 6 January 2007 ; accepted in final form 5 June 2007

Assessment of quadriceps endurance is of interest to investigators studying human disease. We hypothesized that repetitive magnetic stimulation (rMS) of the intramuscular branches of the femoral nerve could be used to induce and quantify quadriceps endurance. To test this hypothesis, we used a novel stimulating coil to compare the quadriceps endurance properties in eight normal humans and, to confirm that the technique could be used in clinical practice, in eight patients with advanced chronic obstructive pulmonary disease (COPD). To validate the method, we compared in vivo contractile properties of the quadriceps muscle with the fiber-type composition and oxidative enzyme capacity. We used a Magstim Rapid² magnetic nerve stimulator with the coil wrapped around the quadriceps. Stimuli were given at 30 Hz, a duty cycle of 0.4 (2 s on, 3 s off), and for 50 trains. Force generation and the surface electromyogram were measured throughout. Quadriceps twitch force, elicited by supramaximal magnetic stimulation of the femoral nerve, was measured before and after the protocol. Quadriceps muscle biopsies were analyzed for oxidative (citrate synthase, CS) and glycolytic (phosphofructokinase, PFK) enzyme activity and myosin heavy chain isoform protein expression. The time for force to fall to 70% of baseline (T₇₀) was shorter in the COPD group than the control group: 55.6 ± 26.0 vs. 121 ± 38.7 s (P = 0.0014). Considering patients and controls together, positive correlations were observed between T₇₀ and the proportion of type I fibers (r = 0.68, P = 0.004) and CS-to-PFK ratio (CS/PFK) (r = 0.67, P = 0.005). We conclude that quadriceps endurance assessed using rMS is feasible in clinical studies.

skeletal muscle fatigue; magnetic stimulation; myosin heavy chains; oxidative capacity

This article has been cited by other articles:

				A. K. Stubbings, A. J. Moore, M. Dusmet, P. Goldstraw, T. G. West, M. I. Polkey, and M. A. Ferenczi Physiological properties of human diaphragm muscle fibres and the effect of chronic obstructive pulmonary disease J. Physiol., May 15, 2008; 586(10): 2637 - 2650. [Abstract] [Full Text] [PDF]

				H. R. Gosker and A. M. W. J. Schols Fatigued muscles in COPD but no finishing line in sight Eur. Respir. J., April 1, 2008; 31(4): 693 - 694. [Full Text] [PDF]

				M. Amann and J. A. L. Calbet Convective oxygen transport and fatigue J Appl Physiol, March 1, 2008; 104(3): 861 - 870. [Abstract] [Full Text] [PDF]