While reading Change of rules likely to herald a new approach to prop culture I was remembering playing rugby at school as a prop in the 1970s. Then (and maybe this was to protect us from adult risk) the scrum grouped, came together, paused and only then pushed). This was fun while I was playing tight head but made my left shoulder very sore when I had to play loose head because I was pushing just as hard but with only one shoulder. How do the grownups manage in this position when they have to come together from a yard away? I think it would be miserable being a loose head prop, having to subject your left shoulder to such punishment especially when the rest of the scrum has it easy in comparison.
The key is to lock the free arm against the opposing prop so that you can exert as much force as possible with that side. You don’t just drop your hand to the side and push with one shoulder.
Goodness, where should I begin? Well, I’ve played tighthead on a mens club for about 3 years now, but have only played loosehead during 10s matches. I’m not sure exactly what you’re asking, but I’ll tell you a little bit about how I position myself during a scrummage. My first move is to try and glance the top of my head off the losehead’s cheek. What this does is pry him away from the hooker, so he can’t support him as well. My second move is to clamp down with my right arm, to twist him towards the ground. (For those that are still reading that don’t know, your head goes to the left of your opposite’s head, and the two props support (or “prop”) a hooker, who strikes at the ball with his foot.) What this does is gets him in poor body position to push.
On the other hand, the looshead is trying to dig his head under my chest, so he can lift up with his neck and lift me off the ground. Although the new rule is going to make the scrums more safe, it’s not going to be nearly as fun. If they simply put in a “pause”, it’d be ok, but they’re calling for an almost complete pre-bind. I agree that it’s definately going to change front-row mechanics extensively.
To answer your question about how the loosehead manages now? I have no idea, I’ve never liked the position.
Left shoulder? That’s the one that’s not engaged - how’s it getting sore?
–Mal, either-side prop of many years’ standing.
I’m wondering what the American members of SDMB are making of this thread 
“My first move is to try and glance the top of my head off the losehead’s cheek. What this does is pry him away from the hooker, so he can’t support him as well.”
must be causing some serious concern. Better not mention the shared bath afterwards.
After I have enough pints to dull the pain, I don’t care who finds out about the bath!
We are talking the Front Row here - a bunch of big, heavy guys, with a requisite lack of imagination so they don’t figure out that the real game of rugby is played by the backs while they take all the knocks 
In fact, an old work colleague (and rugby referee) suggested that the only point of scrums, rucks, and lineouts was to keep the forwards busy so the back line could move the ball and play the game.
To be fair, I think that the new scrum setup will not change the drive too much - refs don’t seem to allow the engage to have too much of an effect (they seem to reset the scrum more these days), and mass and technique will still win the day.
Si
Go comb your hair, we’re busy having a conversation here. 
The new rule will, however make the halfback putting the ball into the scrum immediately after engage less effective than it used to be, rather than waiting for the scrum to stablize.
Like all the new tactics used in the lineout since lifting was allowed, there will be a change of tactics round the put-in to signal the drive or try to offbalance the opposition.
It will change, but not by much.
Si