The basic plank is a great exercise for strengthening the core, preventing back pain, and maintaining overall stability and posture. It is not the most exciting movement in the world, but there are many variations that can challenge and involve other muscles. One such exercise is the X-plank. You may not be familiar with it. Neither was I until my editor gave me the challenge to do it every day for a week. Once again, I can't thank her enough.

Annoyingly, there are several moves with the same name. The static version goes like this: get into a plank position, but keep your arms and legs outstretched. I did mine for comparison: I found it instantly worked my lower torso and outer thighs. I would do it again. But I wanted to try the dynamic version, where you go from a plank to a downward facing dog position and tap each lower leg and ankle with the opposite hand. For the first few days of the Challenge, I wished I had gone with option 1.

This move of course strengthens the core and works it hard, but it also improves flexibility (or lets you know you're not very flexible), increases range of motion in the hips, and stretches the calves. Stability is important for good form, since you'll be balancing on one arm or the other. There is a lot going on here. If you are a yoga practitioner, you will find this move much easier than someone like me who thinks chair pose is the same as sitting pose.

Another thing is that if you do this move wearing a loose-fitting T-shirt or top, the T-shirt will roll up and over your face. This is not a good look.

Here's how to do the X plank with perfect form:

Unless you are a yoga practitioner, you will find this move unnatural and difficult to begin with. That was the case with me. On the first day, I felt it everywhere: shoulders, arms, glutes, and abs. I also felt a good stretch in the backs of my legs. But I was competing for reps to maintain the illusion of decent form. I managed to complete three sets of eight, but I couldn't reach my ankles. I was convinced this was because I was not raising my hips high enough. When one is so focused on touching or reaching a particular point, it is easy to neglect the movements that make it possible. Instead, we try to extend our arms just a little more. They forget that the solution is above the waist. By the end of the last set, I was out of breath, a sign that I had forgotten to breathe in and out as I progressed through the phases of the exercise. I had to put on shoes or go barefoot, or I might slide down to the floor slowly and embarrassingly.

On day two, as always, I decided to focus not only on the goal (touching my ankles), but on how to get there as smoothly as possible (lifting my hips) and on moving my entire torso. This time I felt my back stretching. If that wasn't enough, I found that I could reach the bottom of my shins and near my ankles. Breathing was somewhat restricted in this position, so I concentrated on slow, regular breathing to make sure I could comfortably complete the set.

The next day I was able to add a couple of reps to each set. I then went for a run, and this movement was surprisingly effective in warming me up. I was loose and relaxed.

By the fourth day, I could touch my ankles without stretching them to the point of discomfort. This was quite an improvement over the first day, and I attribute it to patience and focus. When stretching to touch the ankle, it is important to keep the back and legs straight, which is not as easy as it sounds. I tended to forget to raise my hips to the point where I could comfortably lift them.

On the last few days, I increased my reps even more and finished with 3 sets of 15 reps. Although the reps did not increase significantly, I was able to touch my middle leg on the last day, and my reach improved to my surprise. In just seven days, I had better form, more reps, and a greater range of motion. This is a success.

If yoga is part of your fitness routine, there is not much to gain from this move. Just watch out for loose t-shirts.