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Respiratory muscle work compromises leg blood flow during maximal exercise
C A Harms1, M A Babcock, S R McClaran
1John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin, Madison 53705, USA.
Summary
High work of breathing during maximal exercise reduces blood flow to leg muscles. This impacts oxygen delivery and consumption in locomotor muscles, affecting exercise performance.
Area of Science:
- Exercise Physiology
- Cardiovascular Physiology
- Respiratory Physiology
Background:
- During maximal exercise, the respiratory muscles demand significant blood flow.
- It is unclear how this demand affects blood flow distribution to locomotor muscles.
Purpose of the Study:
- To investigate the impact of varying respiratory muscle work on locomotor muscle blood flow and oxygen consumption during maximal exercise.
Main Methods:
- Seven male cyclists performed incremental exercise tests to determine VO2max.
- Exercise bouts at VO2max involved manipulated inspiratory muscle work (unloading, loading, control).
- Measurements included leg blood flow (thermodilution), vascular resistance, and oxygen consumption.
Main Results:
- Increased work of breathing correlated with reduced leg blood flow and increased leg vascular resistance.
- Reduced leg blood flow and oxygen consumption were observed with higher respiratory muscle work.
- Total maximal oxygen consumption was unaffected by respiratory loading, but decreased with unloading.
Conclusions:
- Work of breathing during maximal exercise constricts locomotor muscle vasculature.
- This compromises blood flow and oxygen delivery to locomotor muscles, impacting exercise capacity.