[Walking in the International Four Days Marches Nijmegen: an estimation of the risks]

In 2006, the annual Four Days Marches in Nijmegen, the Netherlands, were cancelled after the first day because two participants had died, and many had become unwell while walking in unusually high ambient temperatures. During the 2007 edition, an observational study of the physiological impact and health risks for walkers was carried out. This time, the ambient conditions were mild. Most participants (90.7%) finished the march without serious complaints or clinical complications, despite significant disturbances in fluid balance and electrolytes. The training level of the participants varied considerably. If we compare the results of this physiological study with studies during marathons, similarities in physiological adaptions are found, most probably due to the same biological mechanisms. However, the participants of the Four Days Marches are incomparable with long-distance runners. There is as yet no well-founded advice concerning the fluid intake of Four Days Marches participants. Increase or decrease in body weight may be an interesting diagnostic tool to measure the risk of dehydration or overhydration.