According to Tolweb.org, the primary disadvantages of bipedalism include slower speed and a strain placed on body parts that are not well designed for upright walking. When a mammal walks upright, the upper body puts a strain on the lower parts of the body. Bipedal mammals must also rest more often than animals which walk on four legs since they cannot rest one leg at a time.
The human body has many adaptations to bipedalism, as described by PBS.org. These include the design of the foot as a shock absorber, the double curve of the spine to support weight and enlarged, weight-supporting surfaces of the vertebrae. However, these adaptations do not completely negate the disadvantages of bipedalism. PBS.org notes that humans do experience back injuries and pain as a result of bearing weight on their spines, which originally evolved to serve more as a suspension bridge for the body's organs than a weight-bearing structure.
A research article published in the journal Naturwissenschaften in 2010 describes several disadvantages of bipedalism that presumably prevent quadrupedal primates from utilizing a bipedal gait. These include its slow speed, which cuts into the valuable time needed to forage for food and inhibits the ability to flee from predators, and the high energy consumption associated with bipedal gaits compared with quadupedal gaits.