Core strength

Are you worried about how your core looks or do you want to run fast. What are your PR's

Perhaps you're doing the wrong exercises, then. Can you do 100 sit-ups?

To Top Runner, I want both, to be honest. My PRs are 14:42 for 5k, 31:01 for 10k, and 24:56 for 8k. To core dump, I may be doing the wrong exercises. I can do 100 sit ups with almost no trouble; I do about 1500-2000 sit-ups/other core exercises almost consecutively (with very short breaks) almost every day, which is why it's not making sense my core is weak.

wow you suck.

should have run D3.

dude, you gotta do weighted abs, or something that is more challenging than mindless crunches at huge quantities. you think people get jacked doing 1000 bicep curls with 2lb dumbbells? or bench press the bar over and over again for a big chest?

You've been misled by the charlatans in the running world who call themselves experts. Here are the facts:

1) The two factors that determine the appearance of your "core," it's degree of muscularity and predisposition to store fat, are determined genetically. MOST people will NEVER have ripped abs no matter what they do.

2) The "core" training you do is completely, utterly worthless. Like every other muscle, those of the midsection should be exercised with brief, hard, infrequent bouts of effort—a few minutes of hard weight training once or twice weekly), not the garbage you're doing. But even correct training will not get you the ripped abs you want for reason #1.

I agree with no wonder.

You should have quickly progressed from simple crunches to a wide variety of core exercises which are designed to isolate and improve all of the many muscles involved with the core.

Most of the exercises will have various levels also. The exercises can be made more difficult by using exercise straps (light, then medium, then strong, x-strong straps).

Eventually you should be able to do this:

https://www.youtube.com/watch?v=lAp9wNEvabk

crunches and sit ups are not healthy and every training organization has distanced themselves from them. Other complex movements are better.

I do not know what year you are in, but if does are PR's that you did the past year then do not change anything even if it is not showing up by the image of your body it is still their because you are running faster. Most of these trolls will never reach 16:20 for the 5k or 35:00 Minutes for the 10K so do not listen to them. Just keep doing you.

Can someone give me a specific example of types of "complex movements" and weight based core exercises? I'm not sure what you mean by that.

olympic lift variations. Farmers walks, waiters walks, palloff presses, pull ups, push ups and variations of those. These are some of the exercises in vogue and most big shots in the training world feel that sit ups/crunches compress the discs in the back and ultimately can do more harm than good.