NOW, all of that being said, I literally can not watch my H/J friends lunge horses for the most part. They either don't use anything but the line or more recently, I've seen something called a neck stretcher. So, to go on a rant... I really just need to say that unless the sole goal of lunging is burn energy off (or perhaps assess lameness), I really don't see any point to lunging without side reins at all. Further, I actually think the neck stretcher is particularly terrible. If the horse wants to bring their poll up, they can't without resistance. It's easy for them to be crooked and there is very little actual bit pressure that would even remotely mimic a true connection to the bit.
So, all of this to say that all the time I just want to scream SIDE REINS to everyone I see lunging.

https://www.horze.com/lunging/horze-adj ... rce=google