We must remember that David and his men had travelled not only from Ziklag to Besor, but before that also from Aphek to Ziklag. They were all tired and those who were not so strong/accustomed to travelling would have struggled. Many of them were likely travelling on foot and carrying heavy equipment.
9 Et David se mit en marche, lui et les six cents hommes qui étaient avec lui. Ils arrivèrent au torrent de Besor, où s'arrêtèrent ceux qui restaient en arrière.