Ventilatory muscle fatigue in prolonged exercise

Author

Betty R. Lawton

Date of Award

12-1990

Degree Type

Thesis

Degree Name

Master of Science

Major

Kinesiology

Major Professor

Edward T. Howley

Committee Members

Jean Jeeves, Craig Wrisberg

Abstract

Maximal Voluntary Ventilation (MVV) measured in time segments ranging from 12 seconds to 1 minute has been utilized in some studies to determine if ventilation is a limiting factor in exercise performance in normal subjects, athletes, and in those with respiratory diseases. Some investigators have claimed that it is inappropriate to use the short-term MVV to analyze ventilatory muscle endurance and propose, instead, the measurement of the maximal sustainable ventilatory capacity (MSVC) in studies of this nature. The MSVC is a test that measures the maximum ventilation that can be sustained for 15 minutes. The purpose of this study was to determine if changes in the MSVC and endurance time of the ventilatory muscles was affected by prolonged exercise. Ten healthy, non-smoking men and women volunteered for the study. The highest rate of ventilation that could be maintained for approximately 15 minutes was determined on one day utilizing a ventilatory apparatus that regulated the rate of air flow through the system, provided saturated air, and allowed partial rebreathing of CO₂. On a day when no exercise was performed, subjects hyperventilated at the designated rate for as long as possible. The following day, the subjects ran for 30 minutes, and eventually to fatigue, at a pace that required an oxygen consumption of 70-80% of their VO_2max. The subjects then attempted to repeat the MSVC rate and time that was achieved the day prior to the run. One-tailed paired t-tests on the MSVC and MSVC time showed significant differences in the pre-exercise and post-exercise values (p < .05). The peak exercise ventilation represented 72.6 +/- 12.8% of the pre-exercise MSVC and 50.5 +/- 8.86% of the pre-exercise MW measured for 15 seconds. The results of this study suggest that ventilatory muscle fatigue can occur in healthy adults of average fitness who participate in prolonged exercise. Possible mechanisms for fatigue include decreased ventilatory muscle efficiency, decreased blood flow to the respiratory muscles, increased O₂ cost of breathing, decreased rate of lactate removal, and/or increased rate of lactate accumulation.

Recommended Citation

Lawton, Betty R., "Ventilatory muscle fatigue in prolonged exercise. " Master's Thesis, University of Tennessee, 1990.
https://trace.tennessee.edu/utk_gradthes/12704