Muscle endurance: Is bipedalism the cause?

One may ask if the transition to bipedalism from condition of quadrupedalism, which occurred about 7 million years ago, has been cause or consequence a series fundamental physiological muscular aspects including cost locomotion, crucial determinant endurance, found be significantly lower in humans than apes. This issue strictly links unsolved issues regarding significance several structural and functional adaptations, classically attributed its associated locomotions, we cannot simply attribute acquisition upright position directly indirectly contribute observed changes muscle energetics that make modern human an exceptional endurance walker runner compared quadrupedals.