Some videos demonstrating core exercices can be found at:
Let it be known, the era of the 800 daily crunches is over. And, this isn’t just because we’re concerned about hip and lower back health; would you believe that you can actually screw up your shoulders with inappropriate core training? Here’s what happens…
The rectus abdominus runs from your rib cage down to your pelvis; when it shortens, it pulls the rib cage down toward your feet. So, as you can imagine, if the rectus abdominus is tight, it can pull the whole rib cage too far down — making you look more like Quasimoto than someone who actually trains hard.
Beyond just the fact that poor posture isn’t all that aesthetically appealing and actually makes you appear smaller, excessive kyphotic postures have biomechanical implications at the shoulder girdle. When your thoracic spine gets too kyphotic, the scapulae abduct (protract) so that they slide outward on the rib cage (toward your arms). This repositions the aforementioned acromion process, as the entire scapula becomes anteriorly tilted. An anteriorly tilted scapula dramatically increases the risk of impingement on those rotator cuff tendons.
How do we counteract this problem? As Mike Robertson discussed in detail in Core Training for Smart Folks, we need to prioritize exercises for the posterior fibers of the external obliques, as these exercises will posteriorly tilt out pelvis without pulling the rib cage downward.
And, by increasing the strength of these muscles, we’ll take some of the burden off the rectus abdominus and shift things back into balance. When I see this problem, I drop all traditional trunk flexion movements (pulldown abs, crunches — and people should know to not do sit-ups by now) and replace them with pure stabilization movements (prone and side bridge) and “lower ab” exercises, most notably the reverse crunch.
Core Training for Smart Folks by Mike Robertson
Functional Ab Training for Bodybuilders by Kevin Weiss