By Don Williams
B.Sc., M.Chiro., ICSSD., PG Dip. NMS Rehabilitation,
Cert. DNS. Memb: CAA, FICS, CEA.
Effective lifting mechanics are an important aspect for our everyday lives. Patients often complain of low back pain and have not considered lifting or squatting technique as a factor in their complaint.
It really doesn’t matter whether you are lifting 100kg of weights on a bar or a tissue off the floor, correct form and technique is important.
One of the major problems which does catch people out is the magnification of force with loads in front of the body.
Low back mechanics are very complex, as demonstrated by the picture to the right (technical biomechanics are available in this link). http://cnx.org/content/m42175/latest/?collection=col11406/latest
For lifting mechanics, we have a range of different lever classes and a stack of joints involved (ankles, knee, hips, spinal segments, shoulders elbows and wrists). But to put it in relatively simple terms, if you think of the low back as a pivot point, the lumbar extensor muscles are only 2-5 cm from the pivot point, when we lift, it is quite easy to have the load out in front 50cm. This can easily give us a magnification of force by 10 to 20 times the load. Essentially, this means that even though it is only 5kg you are lifting, the required compressive load in the lumbar extensors may be 100kgs. Wow!
Lifting with a straight back is not correct
There is a common misconception in the general population that we should lift with a straight back. (See diagram on right)
Many people interpret this as that the back is perpendicular to the ground. Lifting in this manner pushes the knees in front of the toes and necessitates lifting the heels off the ground to lift items at floor level. This increases load on the hips and knees, causes a lack of balance and a decreased lift capacity.
Don’t use you back
We certainly shouldn’t lift bending forward from the hips either.
As in the earlier explanation of lifting mechanics and lever arms, bending forward from the hips and lifting using the low back (like a crane) dramatically increases the likelihood of needing to see the team at Institute of Sports and Spines more often. We often hear complaints from people suggesting that using the hips and knees causes the knees to ache, commonly, when we assess the lifting mechanics with these people they are pushing too far forward with the knees causing increased load and pain, when we improve the mechanics, the knees feel much better in the squat position.
Neutral Spine Position
When standing up straight and tall in good posture we have a lumbar lordosis and thoracic kyphosis. This “neutral” position of the spine is what we should strive to maintain when lifting and squatting. Effective use of this position should see the knees stay in line with or behind the toes, good balance capacity and effective use of the gluteal muscles as the main drive for the movement.
Additionally, good squatting technique should see alignment of the knees in the midline of the foot. In Prague school terms, this would be referred to as good “centration” of the joints. Poor alignment of the feet, knees and hips often contributes to pain on the inside of the knee or the outside of the hip (Trochanteric bursitis)
Poor Centration Good Centration
Correct Squat (lifting) technique
At the bottom of the squat the lumbar lordosis should be maintained. Putting this into simple terms, this means that as you squat down, there will be a point at which the low back starts to “flatten out” and reverse the curve, this is the bottom of the safe lifting range and will be different from person to person. The knees should be in the midline of the foot and the knees should always be behind the toes. The feet should be straight or at maximum 15 degrees externally rotated (pointing out)
A great drill to assess your squat mechanics and to improve your function is to stand with your toes touching a box (or bedside table at home will work). It may be a good idea to put a chair behind you as some people will overbalance and fall backwards when they start this exercise. Slowly squat down, as if you were planning on sitting on the chair, and try to feel the point at which your back starts to move or flatten out. Try to ensure that your knees do not touch the box and that the knees stay in the midline of the feet. If you tend to collapse into the chair when you start this exercise, don’t lose heart, keep at it, reach out in front with the arm, the glut strength will build and this should become easier over a number of weeks. Try this 2-3 times per day, 10 reps each time for 6 -12 weeks until this pattern is easy and natural feeling.
Other Factors to consider
The last thing to mention in wrapping up is that when lifting load at work and around the home, weight is not the only factor which causes issues. The NIOSH guidelines are essentially internationally guidelines and equations which help to identify safe lifting practice and application in the workplace, the following links are very useful for those interested in learning more.
The following is a summary of the modifying factors for your consideration.
Increased weight. This is a no brainer, the heavier the load the harder it is to lift and to a degree, the more the risk. A good start point for safe working loads for 1 person are generally 15kg for females and 25kg for males.
Safe Lifting Zone. We tolerate and accommodate lifting loads between the knees and the shoulders fairly well, when the loads are above or below these points, the weight must be reduced.
Distance lifting (vertical or horizontal). Lifting an object from the knees to the shoulders repetitively is more difficult than just lifting from a bench at hip height to a bench 10cm higher.
Distance from the body. The further away from the body (out in front) the load is, the higher the relative load is on the back.
Repetitions or number of lifts. The more often you have to lift the load, the more the force summates on the back (and the body in general) and once again the greater the risk.
Object Size or Shape. Lifting a really big box (hopefully an exciting present) feels much heavier than a dumbbell of equal weight.
Constant vs Dynamic Load. If the load keep changing weight (a squirming child) it is a more difficult lift than a static load (a sleeping child).
If you have any further question or would like to work through lifting mechanics, please contact the team at Institute of Sports and Spines for more information.