Yes, I feel your pain. Abdominal workout places a lot of stress on the back area – whether lower, middle or upper back, and even neck.
From my experience I have learned it is better to perform lower number of repetitions and perform them correctly and most of all slowly – it gives much better effect and puts less stress on the back and neck – in my case neck, because I tend to “pull” with the neck when performing crunches, pareticulalry when I was performing lots of exercises (once a week I had a training of 1000 abdominals – they were performed quite quickly and when the abdominal muscles got tired, neck muscles tend to help – which is of course wrong)
Planks are a great form of exercise you can use to work on your core and to some degree shoulders and chest, but most of all your back muscles: place your body on your toes and elbows and make sure to form a straight line – no sinking your butt in and no sticking your but up If you form a straight line, this means your abs and back muscles are doing most of the work. Stay in this position at least 30 seconds, then rest for 30-60 seconds and repeat 2-3 times.
There are few variety of planks – feet together or feet wide apart. When you are ready to get advanced: one leg in the air and then the other, or one arm in the air (these two are great for stability). These types of planks are static. There are also dynamic planks – which means you are slowly and with control moving your butt up and down. No super fats movements – the trick is in controlling your movement.
There are side planks too - great for side abdominals or obliques (no more love handles) – lay on one side and support your body on the side of your feet and your bottom elbow. Make sure from toes to head your body forms a straight line. Repeat on the other side. Again, for advanced – one leg in the air, and again there is dynamic variation where you slowly and with control controlling move your hips up and down.
It is also recommendable to perform back exercises that will help you to strengthen your back muscles – after every set of abdominal exercises perform the same number of repetitions of back exercises.