Maximal backpack load for long distance hiking

Thirty-two subjects marched 20 km with 3 different back loads; 20, 25 and 30 kg. Their heart rate, rectal temperature and VO ₂max, immediately following the march, were compared to initial values. A mean drop of more than 20% in VO ₂max was found in the group carrying the 30 kg load, while no significant decrease in VO ₂max occurred in the subjects carrying 20 and 25 kg loads. No correlation was found between the change in VO ₂max and the weight of the subjects or the percentage of the load from the body weight. Since those who carried the 30 kg load were in excellent physical condition (VO ₂max more than 50 ml O ₂/min x kg B.W.) and those who carried the 25 kg load were only of a good one (VO ₂max 40-49 ml O ₂/min x kg B.W.), it is suggested that to avoid significant decrease in VO ₂max, the maximal back load carried by an individual in good physical condition for long distances under field conditions, should not exceed 25 kg.