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1 Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1; 2 Laboratoire des Sciences du Sport, Unité de Formation et de Recherche en Sciences et Techniques des Activités Physiques et Sportives, 25030 Besançon Cedex; and 3 Faculté des Sciences du Sport, Université de Montpellier, 34090 Montpellier Cedex, France
O2 uptake
(
O2) kinetics and electromyographic
(EMG) activity from the vastus medialis, rectus femoris, biceps
femoris, and medial gastrocnemius muscles were studied during
constant-load concentric and eccentric cycling. Six healthy men
performed transitions from baseline to high-intensity eccentric (HE)
exercise and to high-intensity (HC), moderate-intensity (MC), and
low-intensity (LC) concentric exercise. For HE and HC exercise,
absolute work rate was equivalent. For HE and LC exercise,
O2 was equivalent. O2 data were fit by a two- or
three-component exponential model. Surface EMG was recorded during the
last 12 s of each minute of exercise to obtain integrated EMG and
mean power frequency. Only in the HC exercise did
O2 increase progressively with evidence of a slow component (phase 3), and only in HC exercise was
there evidence of a coincident increase with time in integrated EMG of
the vastus medialis and rectus femoris muscles (P < 0.05) with no change in mean power frequency. The phase 2 time constant was slower in HC [24.0 ± 1.7 (SE) s] than in HE
(14.7 ± 2.8 s) and LC (16.7 ± 2.2 s) exercise,
while it was not different from MC exercise (20.6 ± 2.1 s).
These results show that the rate of increase in
O2 at the onset of exercise was not
different between HE and LC exercise, where the metabolic demand was
similar, but both had significantly faster kinetics for
O2 than HC exercise. The O2 slow component might be related to
increased muscle activation, which is a function of metabolic demand
and not absolute work rate.
muscle action; muscle fatigue; cycling; surface electromyography
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