Ventilatory responses to prolonged exercise with heavy load carriage

• Published in: European journal of applied physiology Vol. 116; no. 1; pp. 19 - 27
• Main Authors: Phillips, Devin B., Stickland, Michael K., Petersen, Stewart R.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.01.2016; Springer Nature B.V
• Subjects: Adult; Anaerobic threshold; Biomechanics; Biomedical and Life Sciences; Biomedicine; Evacuations & rescues; Exercise; Exercise - physiology; Exercise Test - methods; Fitness equipment; Human Physiology; Humans; Load; Lung - physiology; Lung Volume Measurements - methods; Male; Metabolism; Muscle strength; Occupational Medicine/Industrial Medicine; Original Article; Respiration; Respiratory Muscles - physiology; Respiratory system; Sports Medicine; Tidal Volume - physiology; Vital Capacity - physiology; Walking - physiology; Weight-Bearing; Canada; Ventilation; Respiratory muscles; Exercise; Operating lung volume; Breathing pattern; Load carriage
• ISSN: 1439-6319; 1439-6327; 1439-6327
• DOI: 10.1007/s00421-015-3240-7

Purpose 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.