Here is a useful article from Physio Answers on the best and worst squat positions and the effect on the lumbar spine. Take home messages are
- Make sure the spine remains neutral during squatting, do not allow spinal flexion at the bottom of the squat.
- Spinal bracing helps to increase intra-abdominal pressure therefore better protecting the spine under load and preventing shear forces
- ‘Each individual will most likely have an ideal squat technique based on their goals and individual differences in boney structure, injury history and mobility.’ We are all different and may not be suited to every exercise. Find methods that work for your body type and shape.
Though I am not one for heavy weight lifting, preferring body weight training as strength work, it is useful to be aware of the difference in stresses for those that do.
Article: http://www.physioanswers.com/2016/02/are-deep-loaded-squats-bad-for-lower.html?m=1