When done wrong, the ab wheel is not just ineffective, it is unsafe and can actually harm you. Now I know what you all are thinking, that any exercise done wrong can be dangerous. My beef with the ab wheel is that it is a complex exercise that is not easy for a beginner to do, while other exercises are easier and can give you more benefit.
1. Take a deep breath in
Before each rep, take a deep breath into your stomach as if you were trying to fill your entire abdomen with air. Then brace your core as if you were about to take a punch.
2. Use your lats
At the beginning of each rep, tighten your lats by pulling your shoulders down and back. This helps to stabilize your spine in a manner similar to when you do a Deadlift. At the bottom position, roll yourself back to the starting position by pulling with your lats, which is a similar movement to a Straight-Arm Pulldown.
3. Start with the wheel directly under your shoulders.
To keep your core engaged, the ab wheel or barbell should start directly under your shoulders at the start and finish of each rep.
4. Keep your shoulders and hips aligned
To perform the Rollout effectively, ensure that your hips and shoulders are aligned with the same form as a proper Plank. If your hips dip, that means you're placing unnecessary stress on your spine.
5. Avoid shooting forward with your hips
One of the worst mistakes is driving downward with your hips as you lower in the rollout. This all but guarantees you will cause your lower back to arch and take the tension out of your abs, which puts your spine at risk and decreases the training benefit. To counteract this, keep your hips straight or slightly bent throughout the exercise, and avoid driving your hips backward as you roll up to the starting position.
IN CONCLUSION:
The ab wheel exercise is simply not worth performing in the gym in terms of risk vs. reward, especially if the one performing the exercise is a beginner. The exercise does not bring your abdominal muscles through a full range and the motion is a complex one requiring you to be hyper-aware of your form.
Not only must one be hyper-aware of their form while performing the exercise, they must also have the strength to stabilize their body while performing the movement. If proper form is not sustained while performing the movement, injury may occur that will have your body crying out in pain and preventing you from exercising in the gym for a long period of time.