Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
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©Journal of Sports Science and Medicine (2008) 07, 395 - 401

Research article
The Role of Active Muscle Mass on Exercise-Induced Cardiovascular Drift
Stylianos N. Kounalakis, George P. Nassis, Maria D. Koskolou, Nickos D. Geladas 
Author Information
University of Athens, Greece

Nickos D. Geladas
✉ Department of Sport Medicine and Biology of Exercise, Faculty of Physical Education and Sport Science, University of Athens, Greece
Email: ngeladas@phed.uoa.gr
Publish Date
Received: 04-03-2008
Accepted: 21-07-2008
Published (online): 01-09-2008
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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


           Key Points
  • The magnitude of the participated muscle mass plays a critical role for the development of cardiovascular drift, when the oxygen consumption per leg is the same.
  • Apart from thermal status and blood volume decline, central command plays a role on cardiovascular regulation during steady state exercise performed with large muscle mass.
 
 
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