The Saxon Side Bend doesn't look like much but it is a beast of a core exercise that can humble you with light to moderate weights.
Due to the arms being overhead, it increases the lever point for the exercise.... when you do that, you make an exercise much, much harder. That is why I would recommend starting this exercise with anywhere from 1kg - 5kg dumbbells (closer to 5kg if you're strong).
This is why a traditional side bend exercise can be done with a lot more weight in comparison.
In addition to working the obliques hard, you will also feel this working the lats, shoulder muscles and the muscles around the spine.
• Stand tall with feet hip width apart and abdominals braced.
• Hold a dumbbell in each hand, arms fully extended over shoulders and parallel to each other
• Bend sideways from waist, tilting upper body to one side. Keep arms parallel
• Should feel a light stretch in lat muscles and oblique muscles down side of body.
• Use oblique muscles (ab muscles at side of body) to pull upper body back to start position.
• Alternate reps with other side of body.
This is my, mostly, Personal Trainer musings and information which I hope you'll find helpful!