Found an abstract for some interesting research that suggests that quadrupedal locomotion can be just as energy efficient as bipedal locomotion.
This is interesting because it conflicts with other research on the subject which has suggested that bipedalism is up to four times more energy efficient than quadrupedalism.
I think that for the average person quadrupedalism would consume four times as much energy to begin with due to lack of skill and poor body mechanics. I find it encouraging that there is research that suggests that each can be as efficient as the other though. I would like to become fully efficient on all fours to see what potential it opens up in terms of speed, power and fluidity of motion.