The side plank is a simple but effective anti-lateral trunk flexion exercise.
With the side of one foot and the same side forearm on the floor with the elbow bent to 90 degrees, hold your body in a straight and rigid line with the shoulders and hips squared off.
The side plank strengthens the trunk’s ability to resist unwanted lateral flexion to improve stability and rigidity.
The side plank can be done for 3-5 sets of 20-60 second holds. Generally with added weight, 20-30 seconds is a good time. They can also be done in intervals for a longer total time, such as 20 second hold and 10 second rest for 10 sets.
Weight can be added with a dumbbell or plate on the hip. The side plank can also be done as lifts of the hip from the floor to the plank position for reps rather than isometric holds.