(54) MULTI-MONTH, ULTRA-ENDURANCE BACKPACKING IMPACTS FUEL SELECTION AND AEROBIC CAPACITY: A CASE STUDY

Purpose: This study aimed to observe the effects of a multi-month backpacking event in the wilderness on aerobic capacity. Methods: An experienced backpacker (30.1yrs; 78.3kg; 179.1cm) completed a wilderness-based backpacking trek known as the Appalachian National Scenic Trail northbound thru-hike. The participant hiked 3,531km and accumulated 99,643m elevation gain over 139 days. Maximal aerobic capacity data was collected at 4 time points (PRE-, MID-, POST-, and 4-WK-POST). Indirect calorimetry via metabolic cart was used to assess maximal aerobic capacity under standardized conditions. Data are reported as percent changes from pre-trek baseline (PRE). Results: The participant lost 2.68kg over the 139-d trek with an increase in aerobic capacity. Specifically, absolute VO₂ max (absVO₂max, PRE 3.960L/min, MID 4.037L/min, POST 4.274L/min, ∆7.93%) and relative VO₂ max (relVO₂max, PRE 50.60ml/kg/min, MID 51.50ml/kg/min, POST 55.90ml/kg/min, ∆10.47%) increased in response to trek demands. 4-WK-POST trek, absVO₂max (2.5%) and relVO₂max (3.36%) returned to near-baseline levels (∆PRE). Trek demands elicited earlier reliance on carbohydrates as the predominant fuel source during maximal aerobic activity testing immediately after the event, evidenced through the time at crossover point (TCP, PRE 3:34min, MID 2:50min, POST 2:32min, ∆-28.97%) and percentage of VO₂ max at crossover point (pctVO₂max_CP, PRE 80.60%, MID 61.36%, POST 49.91%, ∆-30.69%) before trending towards baseline levels 4-WK-POST (TCP, 13.55%) (pctVO₂max_CP, 16.36%). Conclusions: Completing a 139-d independent ultra-endurance trek in the wilderness increases aerobic capacity in response to greater cardiovascular demand, stress, and activity exposure. During maximal aerobic capacity testing, predominant carbohydrate utilization occurs at lower intensities, despite increased aerobic capacity. Upon cessation of marked daily physical activity post-trek, the cardiovascular system swiftly reverts to pre-trek aerobic baseline. Returning to a regular diet post-trek increased the time and intensity of primary fuel source crossover during maximal aerobic exercise, though values failed to reach pre-trek baseline. Practical Applications: To mitigate a rapid decline in aerobic capacity following an ultra-endurance challenge, it may be useful to integrate a post-trek recovery plan that facilitates regular aerobic activity. Further, metabolic adaptations demonstrated throughout the trek may guide extended dietary planning for self-supported ultra-endurance events. Acknowledgements: None