Physiological and performance consequences of heavy thoracic load carriage in females.

The purposes of this experiment were to study physiological responses to graded exercise to exhaustion (Part I) and ventilatory responses during 45 min of exercise (Part II) with and without a 25-kg backpack. In Part I, on separate days, 24 females completed randomly ordered modified Balke treadmill tests. Analysis revealed significant decreases in absolute peak oxygen uptake (3.5%), peak power output (20%), and test duration (40%) under load. There was a significant but modest negative relationship between body mass and the change in test duration between conditions (r = -0.44). While physiological responses to peak exercise were similar, exercise performance was negatively impacted under load. On separate days in Part II, 14 females completed randomly ordered, loaded and unloaded exercise challenges of submaximal treadmill walking at matched oxygen demands. Under load, breathing frequency, dead space, and minute ventilation were increased by 19.9%, 29.8%, and 11.6% (P < 0.05), respectively, while tidal volume and end-inspiratory lung volume decreased by 13.6% and 6.0% (P < 0.05), respectively. After loaded exercise, maximal inspiratory pressure was decreased by 11.5% (P < 0.05) with no changes in maximal expiratory pressure in either condition. Despite matched oxygen uptake between loaded and unloaded exercise challenges, perceived exertion and breathing discomfort were higher (P < 0.05) under load. With heavy load carriage, the altered breathing pattern led to increased dead space and minute ventilation, which likely contributed to higher perceptions of exercise stress and breathing discomfort. These results are similar to previous research in males and underscore the impact of heavy load carriage during exercise.