Quantitation of progressive muscle fatigue during dynamic leg
exercise in humans.
Fulco, Charles S., Steven F. Lewis, Peter N. Frykman, Robert Boushel,
Sinclair Smith, Everett A. Harman, Allen Cymerman, and Kent B.
Pandolf.
Environmental Physiology and Medicine Directorate, Occupational
Health and Performance Directorate, U. S. Army Research Institute of
Environmental Medicine, Kansas Street, Natick, Massachusetts 01760
-5007, Department of Health Sciences, Sargent College of Allied Health
Professions, Boston University, Boston, Massachusetts 02215
APStracts 2:0390A, 1995.
There is virtually no published information on muscle fatigue, defined
as a gradual decline in force generating capacity, during
conventional dynamic (D) leg exercise. To quantitate progression of
fatigue, we developed 1) a model featuring integration of maximal
voluntary static contraction (MVC) of knee extension (KE) muscles
with ongoing DKE and 2) a device that allows frequent rapid transfer
between DKE isolated to the quadriceps femoris muscles and
measurement of KE MVC. Eight healthy men performed both graded and
submaximal constant work rate 1-leg DKE to exhaustion while seated.
Work rate - a product of a contraction rate (1 Hz), force measured at
the ankle, and distance of ankle movement from 900 to 1500 of KE -
was precisely controlled. Lack of rise in myoelectric activity in
biceps femoris of the active leg during DKE and MVC was consistent
with restriction of muscle action to quadriceps femoris. The slope of
the linear relationship between oxygen uptake and work rate was 13.7
ml O2 . watt -1 (r = 0.93). This slope and the increase of heart rate
relative to increasing work intensity agreed with published values
for D leg exercise. Test-retest values for oxygen uptake were similar
(P>0.05) for matched DKE work rates. To track fatigue, MVC (900
knee angle) was performed every two min of DKE. After 4 min of DKE at
work rates corresponding to (mean +/- SE) 66 +/- 2, 78 +/- 2, and
100% of peak DKE oxygen uptake, MVC fell to 95 +/- 3, 90 +/- 5, and
65 +/- 7* % of MVC of rested muscle, respectively (*= p<0.01
from previous work rates). Virtually identical declines in MVC were
observed by the end of both graded work rate DKE and submaximal
constant work rate DKE tests. Quantitation of progressive muscle
fatigue during D leg exercise provides a framework to study the
effects of a variety of interventions on the fatigue process and may
permit unique insights into the involved mechanisms.
Received 30 March 1995; accepted in final form 14 July 1995.
APS Manuscript Number A348-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.