contraction,
Another common exercise is the plank. This exercise works many core muscles in the body, including the abdominals. It can also be performed on all fours with the heels over the toes.
Static holds are a great way to build strength and challenge your mind. You'll find yourself wanting to break out of them very quickly, but it's important to stay focused. They require you to focus on a single task for extended periods of time, and they give you a goal to strive for.
Static pull-ups also strengthen the muscles of the back, especially the latissimus Dorsi (larger back muscle behind your arms). It strengthens your chest and upper back as well as your shoulder muscles. These muscles are important for healthy posture.