Load carriage is a crucial detail of long-distance running, especially when it comes to ultra-marathon distances (>26.2 miles). Longer distances require larger loads to carry fluids and nutrition to maintain performance during these events. Running packs fitted close to the torso are the most popular methods for carrying 1-3 L of fluid, additional food, and gear; however, little is known to what extent load mass may impact running performance. PURPOSE: To identify at which point relative load mass (% of body mass) begins to negatively impact submaximal metabolic efficiency. METHODS: To date, 7 active runners (≥3 days/week, ≥16.09 km/week for the last six months) have participated in this study. Participants (27.9±6.5 yrs; 179.2±4.4cm; 74.68±15.5kg) include males (n=5) and females (n=2) that have undergone four, four-minute intervals on the treadmill at a self-selected pace with relative loads of 0%, 3%, 6%, and 9% of their total body mass using a weighted Salomon running pack. VO2 (ml/kg/min) was measured (Parvo Medics TrueOne Metabolic Measurement System, Sandy, UT) during the last minute of each interval and then averaged for analysis. A repeated measures ANOVA was performed comparing the relative load of 0% to running pack loads equating to 3%, 6%, and 9% of total body mass. RESULTS: There was a strong, positive correlation (R2 = 0.83) between pack load and VO2, although significant differences in VO2 were only observed between the relative loads of 0% and 9% (p = 0.013). CONCLUSION: These data suggest that although a linear increase in VO2 in relation to pack load was observed, pack loads at 9% resulted in a significant increase in VO2, indicating a decrease in running economy. Identifying the relationship between relative load mass and metabolic efficiency may allow runners to better prepare and manage their loads to reduce fatigue during ultra-marathon type competitions.



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