The correct verb to be used in the given sentence is ‘declines’, which according to the above sentence means to come down the steep ascent.
The action which follows after climbing a steep ascent is to go down or decline or descent the steep, meaning a sharp fall from the steep ascent.
The given sentence means that after a steep ascent, the bikers should decline on the slope of the ascent and reach a flat surface and race till it culminates at the finish line.
