"Bend your knees" is probably the oldest lifting instruction, but it’s often ignored. Why? It could be because squatting when grabbing something from the floor takes more energy, according to a report in the July issue of the Archives of Physical Medicine.
In a study involving 20 healthy volunteers, heart rates went up more when they raised and lowered a box by squatting compared to bending over from the waist. The extra energy required to lift safely could explain why people risk back strain by lifting with straight legs, according to the study.