Bicyclists have the willing to choose whether they are walking or pedaling up hills. A declaration states that it should be more efficient to ride up to an approximately limiting gradient than to walk. Because for a common steep hill with a gradient of 15 percent, experiment showed that the efficiency for riding is 17,5 percent, while for walking is 12,3 percent.
As far as I am concerned, this desired movement should have the slope of the steep hill and the physical conditions of the bicyclists as the considerable preconditions. For instance, for the oxygen consumption under the same uphill slop and cycling speed, the amateurs of course behave less sustained as the professional bicyclists, so that after certain travelling path, they would prefer to walk to save energy. In the same respect, if the steep hill is with a high slope, let’s say 58 percent (30 degree), I bet that even though for those profession cyclists, they would opt for walking.
Reference: I. McDonald, Statistical studies of recorded energy expenditures of man. II. Expenditures on walking related to age, weight, sex, height, speed and gradient, Nutrition Abstracts and Reviews 31 (July 1961): 739-762.