Worst Advice: "Lift with your legs"
Almost everyone has heard the advice "lift with your legs, not your back".
This statement is both entirely true, and also some of the worst advice you could give the average person. Without an in depth understanding of BIOMECHANICS and movement patterns the average person will take this advice and go from back injuries to knee replacement surgery in no time.
Lifting with your back
Just look at the shape of the mans back. The first thing you need to understand about picking heavy objects up, is that your back CANNOT ROUND. If a single segment of your spine rounds, most of the pressure from the object is resting on that part of your back. It's a great way to get a herniation or worse.
So he hurt his back, and has now recovered. His doctor gives him a bit of advice. "Make sure you LIFT WITH YOUR LEGS AND NOT YOUR BACK"
With this in mind, he goes back home and eventually has to lift another heavy object. So he remembers, lift with my legs and not my back.
tHIS PICTURE IS ACTUALLY FROM webmd TITLED "Proper Lifting technique". The Problem with this picture, is that it is horrible lifting technique.
Is it lifting with your legs?
Yes.
Is it going to end up killing your knees?
Yes.
Take a look at the starting phase. The knees have sheared forward over the toes and the heels have come off the ground. This forces your quadriceps to do the vast majority of the work. It subsequently causes a huge amount of force to pass through the ligaments and tendons of the knee. You can see this in stage 2 of this picture. There is barely any hinge in the hips, and a very sharp angle on the knees (which are still shearing over the toes!).
Your legs, hips, and back are not supposed to function like this. When picking up a heavy object you should use the stronger muscles in your legs. These muscles being your Hamstrings and Glutes. The above picture takes both of those muscles away from your lift creating a scenario where your knees are vulnerable to injury. You are also building a faulty movement pattern that will eventually leave you with chronic knee issues. In our experience, 9/10 clients who walk in after a back injury try and pick up their first dumbbell exactly like this.
Okay. So then how do I lift the damn box?
Lift with your hips, not your knees!
When you drop down to pick up an object, the first thing that should happen is that your hips should hinge backwards. Your back remains straight the entire time, and then you slightly bend your knees. You can see in the diagram above most of the movement has come from the hip joint, while the knee has only bent slightly (never passing over the toes!)
From this position you should drive through your heels, and extend both your hips and knees at the same rate (meaning your shoulders should never drop below your hips). Lifting from this position allows your posterior chain (hamstrings and glutes) to protect both your knees and back.