Energy Balance During Backpacking

Abstract

PURPOSE: The energy expenditure (EE) of backpacking has been described in only a few studies, and energy balance has never been reported. This study sought to evaluate EE and energy intake (EI) during an extended backpacking trip. METHODS: Three experienced, aerobically fit backpackers (32-yr old female, 57 ml.min-1.kg-1 VO2max; 34-yr old male, 73 ml.min-1.kg-1; 53-yr old male, 62 ml.min-1.kg-1) recorded their heart rate (HR) and food consumption during a five-day, 162-km trip on a rugged section of the Appalachian Trail. Body mass was recorded shortly before the trip began and immediately upon exiting the trail on day five, using the same scale. Resting EE was estimated as 1 kcal/hr per kg. Exercise EE was estimated two ways: (1) ACSM equation for walking, using distance traveled and gross elevation gained; EE of descents was considered equivalent to flat walking in accordance with past research showing that shallow downhill grades require less EE than flat walking, but steep downhill grades require more than flat walking; (2) the HR/VO2 relationship during treadmill testing was applied to average HR values for each subject for each day during walking. RESUITS: Gross EE using the ACSM equation averaged 4062 kcal on four full days, and 2733 kcal on the fifth day. Gross EE using HR/VO2 was 23% greater. EI averaged 2134 kcal on four full days, and 1117 kcal on the fifth day. The largest food source was snack bars and trail mix, which accounted for 62% of EI. Substrates were 52% carbohydrates, 17% protein and 31 % fat. Average HR during hiking was 105 bpm, or 37% of heart rate reserve. Expected average weight loss was 1.2 kg based on the ACSM walking equation and 1.8 kg based on HR/VO2. Actual weight loss averaged 1.7 kg. CONCLUSIONS: Subjects in this study did not maintain weight during extended backpacking. Their weight loss was more accurately predicted by estimating EE from HR/VO2 than from a walking equation.