Question 1: “What's the best way to work on the abs without straining your back much?” – James McEwan
James, if you’re straining your back when you train your abs, then you definitely need to figure out what is going on. It might not be a weakness in your core; it could be something else that you might not have thought of yet.
First off, just as a reference, what is core training?
Essentially, there are two types of core training; isolative and dynamic. Isolative core exercises are static positions where you train the overall stability of your torso. For example, holding a plank for time will train your core stability and teach you how to use your body as a single unit. It will also help you understand how to breathe and brace your midsection under tension. This is an essential component of learning how to remain safe while performing exercises like the squat or deadlift.
Dynamic core exercises are the exercises that you see most people perform in the gym; including pike ups on a Swiss ball, ab rollouts, and one-arm farmer's walks. Dynamic core exercises are just like isolative movements in the fact that they both require you to keep your torso locked in a good neutral (straight) position. The difference with dynamic core exercises, however, is that now your extremities are in motion.
If you are performing your core exercises correctly, but you are still getting pain, you might want to look elsewhere. When you say you’re straining your back, I’m assuming you’re talking about your lower back. This could be an indication of a poor position of your pelvis, referred to as anterior pelvic tilt. This is where the top of your pelvis tilts forward and your butt will look like it’s sticking out. This happens when you sit too much or don’t perform any mobility work on your hips before or after your workouts. I would film yourself doing a push-up or a plank and see if your lower back is sagging downward. If it is, some hip mobility drills should help you to achieve a more neutral pelvis and give you a better position in your lower back when you’re training your abs.