Why did many prisoners suffer from exhaustion during the Bataan Death March?

The prisoners of the Bataan Death March suffered from extreme exhaustion primarily because they were already severely weakened before the march began. Having endured a 99-day siege on the Bataan Peninsula, the troops were already starving, sick with diseases such as malaria and dengue fever, and surviving on minimal rations.1

During the forced march, these already battle-worn and enervated captives were subjected to a grueling pace in intense tropical heat with little access to water. The Japanese military, which had failed to prepare logistically for the large number of prisoners, further exacerbated their physical decline through constant brutality; guards beat the prisoners incessantly, often to force them to maintain the pace. Those who were unable to keep up due to this exhaustion or illness were frequently executed, including being shot, bayoneted, or beheaded.1