The main reason for spotting someone during a back squat should not be to stop the bar from crushing the athlete. It’s to help them through a sticking point and guide the correct bar path. I only use the high bar squat for athletes as in my opinion this is the best way to build strength that transfers to increased athletic performance. The low bar squat I only recommend to be used by competitive powerlifters. The high bar squat is much safer as your torso is upright and as straight as possible, which makes it easy to dump the bar behind and jump forward if you cannot complete the lift. That’s just one more reason why it is so important to squat with correct technique.
Spotting an athlete in this manner helps the adaptation process, as it allows the athlete to push themselves right to their limit, which helps accelerate gains in strength development. If they need a few kilos of help through their sticking point, the spotter can easily and safely provide that help. If the athlete has a tendency lean forward too much the spotter can help keep the bar in the correct path until the the athlete learns to consistently maintain an upright torso position.
These two points of (a) providing limited help through a sticking point and (b) ensuring the lifter maintains the correct bar path are the only justifiable reasons for spotting a back squat. Spotting someone so the bar does not crush them is, in my opinion, not a justifiable reason. When I spot one of my athletes and I am using more than just a few kilos of pressure I tell them to lower the weight. If they are leaning too far forward despite my spotting I also tell them to lower the weight.
One athlete who came to work with me had such a bad habit of leaning forward that they actually dumped the bar over their head. No lie! They were strong but were not supervised correctly when they learned how to squat and got into the habit of dumping the bar over their head. This was the scariest thing I had seen in my life – when I first saw it I almost lost my mind. It was so engrained in the athlete’s motor pattern they did not know how to escape any other way.
I spoke to my mentor, Pierre Roy, about this and he said, “you must let the athlete find their way, do not try and teach a new pattern of survival with heavy loads”. So they practiced with light loads, with the intention of erasing their old pattern so they do not revert to it when they encounter that situation again. What I did was have the athlete dump the bar off their back behind them on the last set of squats every workout. When their squat workout was done they would just dump the bar behind them and move on to the next exercise. I was careful not to instruct them on how to lose the bar in an actual survival situation because they only have a split second to make up their mind as to what to do. Hesitating in such a situation is a recipe for disaster.
Spot to help an athlete through their sticking point, providing no more than a few kilos of help. Spot to keep them on the correct bar path. Never grab the bar suddenly, as it will throw the athlete off and make them lose their balance, which can result in an injury to them or you tearing your biceps. Practice, practice, and practice some more. Like anything else, it takes skill.