#5 Stability Ball
A stability ball is technically not a machine but is a very effective tool in improving the abdomen muscle group and hence, has made this list.
It is highly versatile and could be used as a weight or even as a surface. Using the Swiss ball adds an extra degree of customizability to the workout as it extends the range of motion and thereby, activates more muscles in a single training session.
You could perform a multitude of exercises using the stability ball, making it a great way to add variety to the training routine.
However, plant your back properly and take adequate support while training with the stability ball to avoid injury.
What do you think is the best exercise to tone your abs? Let us know in the comments.