Squats are a powerful move for any athlete. They are also a great exercise to incorporate into a regular workout routine. The squat mainly activates the posterior chain. The glutes, hamstrings, erector spinae, and a few others. The squat is known as a triple extension move. The ankles extend, the knees extend and the hips extend.
As I've said before; injury prevention is superior to treatment but if you train long enough or hard enough injuries are inevitable. Research is now showing the ligaments stiffen up and have less elasticity as load increases. This means the spine does not respond the same way with lower weight vs. higher weights. This transfers more load to the muscle and joints. Essentially the biomechanics of the spine change.
Errors when lifting lighter weights don't have the same effects as errors when lifting heavy weights. The key I want you to pay attention to is to focus on keeping the back straight and in extension. The opposite and poor posture is flexion (rounding of the spine) this opens the low back up for many soft tissue injuries, either to the disc, ligaments, tendons or joints. Torque on the Spine is greater when the torso is at a more bent over angle and the bar is placed higher of the back of the shoulders. The spine is at its greatest compressive load when lifter is at the bottom of the squat phase.
A major cause of spinal flexion when squatting is ankle mobility issues (see previous post and video). When ankle mobility aka dorsiflexion is limited it puts the spine into flexion, rounding the back to move the weight slightly forward to change the center of gravity. This does not cause huge problems at light weights, but as the weight increases the injury potential is increased.