Most guys do not pay attention to minor aspects of lifting that can have major affect on the technique of lifting weights. There are more than one grips that can be used to hold a barbell and different grips have different benefits.
The way most of the guys while doing chest workout hold the barbell is overhand grip in which back of your palm faces towards you. Lifters who use overhand grip most of the time wrap their thumb around the barbell and that is called full grip and closed grips. In closed grip you can squeeze the bar as hard as you could.
Underhand grip is one in which bar is held in a way our palms faces towards us and this type of grip is used while doing barbell curls.
If in overhand or underhand grip your thumb does not wrap completely around the bar than you are using false grip and it could be dangerous to hold the bar with false grip while doing chest workout because there are chances that your hands can slip.
A lot of guys have muscles. A lot of strong men in this world. I think it's important to show that even under all this strength there's a fragile side, thanks for the suggestions @sufyansial
informative post :) very good :) @sufyansial
The reason people use underhand grip is to change the way your rotator cuff is activated. I have torn both of mine, and I have spent a very long time using different grip methods that actually changes the way your shoulder rotates to help with pain and injury.
You can also lose the bar using a regular overhand grip, and most people will even use a overhand grip with their thumbs parallel with the bar or wrapped behind against their index to isolate their chest muscles, because with a full-grip, you are utilizing different secondary muscles to stabilize.
So if you see people using that grip, its not a big deal, they either have injury problems, like me, or are trying to utilize different muscles for an overall build.