Here is a video I found exploring RKC Planking, it is an intermediate video. I have been doing these INCORRECTLY for a long time. I always get lower left back pain just above the glute and I believe it is due in part to poor form...Not trying to hi-jack thread just thought I would share...
[video=youtube;a0xfzXi1jQo]https://www.youtube.com/watch?feature=player_embedded&v=a0xfzXi1jQo[/video]
[video=youtube;a0xfzXi1jQo]https://www.youtube.com/watch?feature=player_embedded&v=a0xfzXi1jQo[/video]