Hello,
I just wanted to mention that you migh want to be be careful with ankle or any weights on the legs when doing abs, as that usually is a sign that the hip flexiors are kicking in and your abs aren't working as hard as they should/could. It depends on the ab exercise of course, but the main althetic abs exercises, if your using your legs, your letting your abs get away with not carrying all the weight they should, and I mean by using, if you are putting weight on your legs and it's actually feels like it's doing something your using your hip flexors some with your ab work. Now if your doing hammer crunches, or double leg extentions then if your very careful and controled you can force your abs to work harder with the weights, but even those, can kick in those hip flexors in a heart beat, with very little help from you. Your abs will still get a workout and feel worked, as things are all tied together, but it's just not as extreame as it could be, I guess you'd say. If your happy with the results, then that might be the way for you, but if your trying to get this to get harder tighter abs, next time try to put your legs in a more nutural position, for some it may be further away from the body others it might be closer as it depends on where you put your feet know as to how to correct it so try it both ways. And when you do your abs pull them in like your trying to hook your belly button on your spine, and then do the exercise while squeezing the abs even more and forcing them to pull your weight up inch by inch, this will help keep the hip flexor out of the ab work. And should make the abs actually do all the work, and not share with their friends the hip flexors.
Good luck and do be careful and always enjoy your workouts,
Kit