Does backpack load carriage weight affect susceptibility to acute mountain sickness during intermittent walking in hypoxia?

Introduction:
The growth of global adventure tourism has led to millions of travellers visiting areas of high-altitude for recreational trekking, charity fundraising challenges and/or cultural immersion over several days to weeks annually. These activities necessitate carrying backpacks that contain hiking provisions of additional weight without understanding how increased load carriage may affect physiological responses at altitude, nor whether they may increase the risk of experiencing symptoms of acute mountain sickness (AMS) - a common altitude illness typically observed above 2500m. There is limited understanding whether existing backpack load recommendations used at sea-level (maximum load equating to 1/3 of body weight) apply at altitude, or whether increasing loads exacerbate symptoms of AMS. The purpose of the study was to therefore assess backpack weight of 10%, 20% and 30% of body weight on physiological and perceptual strain and symptoms of AMS, during a simulated hillwalking test in hypoxia.

Methods:
Thirteen physically active males and females (23±1 years) completed three intermittent walking tests (including: 35-mins rest, 60-min walk [3x20-min intervals with 5-min rest] at 4km.hr-1 at 10% gradient, followed by 15-mins recovery) within normobaric hypoxia (FIO2: 0.13). These were conducted within a randomised order whilst carrying a backpack loaded with additional weight that was either 10%, 20% or 30% relative to the participants’ body mass. Physiological, perceptual and Lake Louise Questionnaire (LLQ) scores were assessed throughout.

Results:
Heart rate and ventilation were higher (both p<0.05) during the 30% backpack test compared to 10% (+13±11 b.min-1 and +9.4±7.6 L.min-1), but no differences were found between 10% and 20%. LLQ scores were higher (p<0.05) during the 30% backpack test compared to the 10% (+2±1 A.U.) and 20% (+1±1 A.U.), but no differences (p>0.05) were found between 10% and 20%. Rating of perceived exertion (RPE: 6-20 Borg [1982]) were higher (all p<0.05) during the 20% and 30% trials compared to 10% (+2±2 and +4±2 A.U.), and also during the 30% compared to 20% trial (+2±2 A.U.). No differences in pulse oxygen (O2) saturation, nor volume of O2 uptake (all p>0.05) were found between tests.


Conclusion:
Carrying additional backpack weight increases markers of physiological and perceptual strain and may augment AMS symptoms. Altitude travellers without prior experience of hiking and who are carrying a backpack for an extended period of time should understand these responses and potential risks to health, as well as educate themselves on safe altitude knowledge/travel and contributing risk factors.