Which is better when lifting: squat or stoop?
For a long time people were advised to squat down to lift a heavy load. Hold the load close to the body and use the legs to lift. The squat lift (knees bent, back straight) was said to be 'safer' than the stoop lift (knees straight, back bent).
There isn't enough evidence to support one method over another. More studies are really needed to clear this mystery up. Many people still prefer to stoop over to lift -- even after instructions to use the squat lift.
New studies suggest the position of the low back may be more important than the choice of stoop or squat. It seems a slightly flexed low back or freestyle (using any method that comes natural) are better than using a swayback or lumbar lordosis during the lift.
The real issue seems more likely lifting while twisting or lifting repeatedly over and over.