Effects Of Carrying A Weighted Backpack On Lung Mechanics In Healthy Men

Abstract

The use of a weighted backpack is common in occupational and recreational settings. However, it is not known if weighted backpacks alter breathing mechanics or increase the work of breathing (WOB). PURPOSE: To determine the effect of a weighted backpack on breathing mechanics during treadmill walking. METHODS: Subjects (n=7, age=28±6 yrs, ht =180±6 cm) completed five randomized exercise bouts on a treadmill: no backpack (NP), an un-weighted backpack (NW) or a backpack weighing 15, 25 or 35 kg. The backpack trials consisted of two 2.5 min stages, while the NP trial had five 2.5 min stages; to ensure there was an overlap in ventilations. An esophageal balloon catheter was used to estimate pleural pressure and calculate the work of breathing. A maximal expiratory flow volume curve was generated for each condition before and after exercise, while inspiratory capacity manoeuvres were performed during each stage to determine end-expiratory lung volume (EELV). RESULTS: Forced vital capacity (FVC) for the 25 and 35 kg pack trials was decreased compared to all other conditions (P<0.01); however, there was no difference between the NP and NW condition and the 15 kg and NW condition (P>0.05). There was no difference in expiratory flows at: peak, 75% FVC, 50% FVC and 25% FVC between all conditions (P>0.05). Two subjects displayed expiratory flow limitation (7-8% of tidal breath) during the final workload of the 35 kg trial. At the same treadmill grade and speed the 25 and 35 kg conditions had significantly different: minute ventilation, breathing frequency, EELV and WOB; when compared to the 15kg, NW and NP condition (P<0.05). There was no difference in the WOB when comparing different backpack weights at similar minute ventilations (P>0.05). At a similar minute ventilation, independent of trial speed and grade, values were different for the 35 kg backpack and NP condition for breathing frequency (27±4 vs. 22±4 bpm; P<0.01), EELV(25±3 vs. 32± 3 % FVC; P<0.01) and tidal volume (2.0±0.3 vs. 2.5±0.5 l; P<0.01), but were similar for WOB (481±200 vs. 407±116 J·min-1; P>0.05). CONCLUSION: Wearing a weighted backpack alters lung mechanics and the breathing strategy employed during mild to moderate exercise in a normoxic environment; without changing the specific WOB. Funding: The Natural Science and Engineering Research Council of Canada