Ventilatory responses to prolonged exercise with heavy load carriage.
OBJECTIVE
The purpose of this experiment was to study breathing pattern and operating lung volume during 45 min of exercise with a heavy backpack (25 kg) and examine the effect of this exercise on respiratory muscle strength.


METHODS
Fifteen males completed randomly ordered graded exercise tests on a treadmill with and without a correctly sized and fitted 25 kg pack. Subsequently, each subject completed, in random order, on separate days, 45 min of treadmill walking with and without the pack. Oxygen demand was matched between conditions (loaded: 3.01 ± 0.11 and unloaded 3.02 ± 0.11 L min(-1)).


RESULTS
With load, breathing frequency (f B) and minute ventilation increased by 21.7 and 15.1 % (P < 0.05), respectively, while tidal volume (V T) and end-inspiratory lung volume (EILV) were reduced by 6.3 and 6.4% (P < 0.05), respectively, compared to unloaded. Following loaded exercise, maximal inspiratory pressure decreased by 6.7% (P < 0.05) with no change in maximal expiratory pressure. No changes in maximal inspiratory or expiratory pressures were observed following unloaded exercise. Despite equivalent oxygen demand, perceived exercise stress and breathing discomfort was higher (P < 0.05) in the loaded condition.


CONCLUSIONS
The mechanical disadvantage placed on the respiratory system during exercise with a heavy pack led to compensatory changes in breathing pattern and EILV, and a reduction in maximal inspiratory pressure post-exercise. We suggest that in an attempt to minimize the work of breathing, subjects adopted a shallow and frequent breathing pattern. However, this pattern increased deadspace and minute ventilation, which likely contributed to altered perceptions of exercise stress and breathing discomfort.
Faculty of Physical Education and Recreation, University of Alberta, 4-427 Van Vliet Complex, Edmonton, AB, T6G 2H9, Canada.
Devin B
DB
Phillips
Department of Medicine, University of Alberta, Edmonton, AB, T6G 2J3, Canada.|G. F. MacDonald Centre for Lung Health, Covenant Health, Edmonton, AB, T6K 4B2, Canada.
Michael K
MK
Stickland
Faculty of Physical Education and Recreation, University of Alberta, 4-427 Van Vliet Complex, Edmonton, AB, T6G 2H9, Canada. stewart.petersen@ualberta.ca.
Stewart R
SR
Petersen
D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D006801:Humans; D008168:Lung / Q000502:physiology*; D008176:Lung Volume Measurements / Q000379:methods; D008297:Male; D012119:Respiration; D012132:Respiratory Muscles / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D014797:Vital Capacity / Q000502:physiology*; D016138:Walking / Q000502:physiology; D016474:Weight-Bearing
Breathing pattern; Exercise; Load carriage; Operating lung volume; Respiratory muscles; Ventilation