Tuck-Up Compression

I'm having trouble getting the required ROM for tuck-ups. I can't get my knees close enough to my chest. Here's what I've worked out:

- I can get either my legs or my chest to the correct position, just not both in relation to each other. So if the legs are in the right position, the chest isn't high enough, and vice versa.
- I can achieve the correct position if I use my arms to pull my knees into my chest.

Is this a strength issue, or a mobility issue? How should I work on correcting it?

If you can pull knees to chest manually but not during a rep the problem is lack of strength. Problem will most likely resolve itself through just following your schedule and doing the tuck ups with the current ROM you have, but you might need to add another minicycle after mastery of your current ROM to add the new ROM to your repititions which might result in less repetitions because of increased intensity