The Regular Plank is one of the best exercises for core conditioning.
It also works on gluteus and hamstrings.
The Side Plank works muscles in your core. It strengthens abdominal and back muscles, gluteus and adductor muscles.
When you don’t have time to workout, just do a couple of planks on the floor. They can be done on the Reformer or on the floor.
You can watch the video below for some examples of these two exercises.