To do the ab wheel exercise effectively, you have to be mindful of many things at once. You have to be certain you are contracting your core enough throughout the exercise to keep your lower back stabilized and prevent it from sagging down. You also have to make sure your hips and shoulders are moving at the same speed. Combine a beginner’s lack of strength and experience in the gym and this can be a daunting task.
The ab wheel exercise requires one to have enough core strength and shoulder strength to properly stabilize themselves during the exercise. If your core is weak and you attempt to roll yourself to a straight plank position with the ab wheel, your pelvis will sag forwards and your lower back will drop. This excessive pressure on your back is terrible for you and will quickly have your lower back screaming for mercy.
Ab wheel exercises are more challenging than they look. Find videos and instructions to do them correctly. Strengthen your abs and stay injury free.
The ab wheel exercise does not take you through a full range of motion when you do it and you are not maximally contracting your abs. There are many exercises out there that will maximally contract your abs and are safer to do.