One of the big developments in core training over the recent past is the use of "plank" exercises. As a personal trainer in her 50s who trains many clients in that age range, I for one am a fan of planking for many reasons. But there are also situations in which this is contraindicated, which I'll discuss a bit later. Let's first look at the reasons that planks are recommended.
In my professional opinion, we can only do spine-flexing crunches for so long until it becomes a problem -- especially for those with osteoporosis (not recommended at all). Imagine taking a metal rod and bending it over and over again a thousand times. It's probably going to break! I'm not suggesting that your spine will break. But I am suggesting that it can only take so much wear and tear before another option is required to strengthen core muscles. Planks are a wonderful alternative, as they increase core strength and spinal stabilization while maintaining a neutral spine, thus eliminating the constant flexing and extending of the spinal column. In addition to that, multiple muscles are trained isometrically at one time, making it a wonderfully efficient exercise -- just the way your body was designed to function.
A "front plank" is one example of a plank exercise that trains many muscles simultaneously. In addition to strengthening the abdominals and low back muscles, the upper body muscles that fire at the same time are the chest, shoulder, upper trapezius/neck, biceps and triceps muscles. Lower body strengthening occurs in glutes, thighs, and calves. Not a bad deal, considering all you have to do is hold this position for a few seconds, right? Sign me up!
The "side plank" is my favorite exercise for training obliques. In addition to engaging many of the previously discussed muscles, it really emphasizes using the obliques to stabilize the spine and pelvis -- key to a healthy spine.
Last, the "reverse plank" isolates and strengthens the gluteal muscles, hamstrings, abs, and low back -- not to mention the upper body muscles holding you up.
As simple as these exercises may look, they're not easy. As with any exercise, if not done with good technique, there is a risk of injury. Here's where the down side of planking comes in. If you feel any neck or low back pain while doing the exercise, this may be an indication of weakness in the upper or lower regions of the spine. If the core is too weak, the spine will sag, causing compression in the vertebrae, pressure on vertebral discs, and/or shoulder joint inflammation. If any of these apply to you, it would be best to first work on building basic strength in these areas with more traditional exercises. Or you can try approaching the plank in a modified position, such as with knees on the floor when doing the front/side planks. This will allow you to work up to the more advanced plank positions.
Additional benefits of plank training include improved posture and balance, making daily functional activities easier. These benefits are awesome, but don't overdo it! When just starting out, I recommend holding the position for shorter bouts of time (5-10 seconds), depending on your level of conditioning. After a week or two, try increasing your time (10-15 seconds), and continue this until you're able to hold the plank for at least a minute. You will see and feel a difference in your body. Again, this is one of those "more bang for your buck" exercises, so go for it and plank your way to good health and fitness!