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JOURNAL
OF
SPORTS SCIENCE &
MEDICINE
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Research
article
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THE ROLE OF ACTIVE MUSCLE MASS ON EXERCISE-INDUCED CARDIOVASCULAR DRIFT |
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Stylianos N. Kounalakis, George P. Nassis, Maria D. Koskolou and Nickos D. Geladas  |
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Department of Sport Medicine and Biology of Exercise, Faculty of Physical Education and Sport Science, University of Athens, Greece |
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© Journal of Sports Science and Medicine (2008) 7, 395 - 401 Search Google Scholar for Citing Articles |
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| ABSTRACT | |||
| The purpose of this study was to examine the role of active muscle
mass on cardiovascular drift (CVdrift) during prolonged exercise.
Twelve subjects with peak oxygen uptake (VO2peak) of 3.52 ± 0.52
L·min-1 (mean ± SD) cycled for 55 min with 80 revolutions per
minute with either two legs (2-legged) or one leg (1-legged). Oxygen uptake
was at 60% of VO2peak throughout the 2-legged trial and at half
of this value in 1- legged condition. Cardiac output (CO-CO2
rebreathing), heart rate (HR) and quadriceps integrated electromyographic
activity (iEMG) were higher (p < 0.01) during 2-legged than 1- legged
exercise. Changes in stroke volume from 20 to 50 min of exercise were greater
in 2-legged than in 1-legged (∆SV: -20.8 ± 0.8 vs. -13.3 ± 1.3 ml·beat-1,
p < 0.05). Similarly, changes in heart rate (∆HR) were +18.5 ±
0.8 and +10.7 ± 1.0 beats·min-1, in 2-legged and 1-legged, respectively
(p < 0.01). Calculated blood volume changes declined significantly in
2-legged exercise (∆BV: -4.25 ± 0.43%, p < 0.05). Sympathetic activation
as indicated by the ratio of low and high frequency in spectral analysis
of HR (LF HF-1 ratio) was higher in 2-legged than in 1- legged
trial (p < 0.05). At the end of exercise, CO had a tendency to decrease
from 20th min in 2-legged (changes in CO = -0.92 ± 0.3 L·min-1,
p = 0.07), whereas it was maintained in 1- legged cycling (∆CO = -0.15
± 0.2 L·min-1, p = 0.86). Multiple regression analysis showed
that HR rise and blood volume decline were predictors of SV drop whereas
heart rate increase was explained by rectal temperature and magnitude of
muscle mass activation, as indicated by iEMG (p < 0.05) in 2-legged cycling.
In conclusion, apart from the well-known factors of thermal status and blood
volume decline, it seems that muscle mass involved plays also a role on
the development of CVdrift.
Key words: Prolonged cycling, cardiovascular regulation. |
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