I am physically unable to do curl-ups

Hey kid, I don't understand what you mean by curls ups related to some abs exercises. Curl is a name given to a bicep exercise. U probably meant Sit ups. Your core is weak,i'm sure you realize it by now. After identifying the problem, plan a solution/

Here is mine that'll get you back on track and boost you to 1st place during PE class:

1) you lack of carbohydrates in your body reason why you feel weak, most of the time. At breakfast get some complex carbs slowly digestive carbs as they say, for instance oat meal, Weetabix, or fruit and fibres cereals. get some grape fruits and 3-4 egg whites. what you do is replenishing the body that has been starving for 8 hours the night before. Believe me you'll feel alot better. depending on when you have your class get a complex carb at least 30mn before hand you'll feel energetic, get an isotonic drink as well, Powerade or gatorade, it'll help you to store back energy during class. use olive oil as well it'll strip the fat out of your 6 packs.

2- I wanna know your age first of all to give you a little workout plan for your abs, since I don't have it I will recommend you to strengthen your lower back first of all. Core includes abs and lower back.
The best for you is to do some abs pull ups with hips and knees flexed at 90° grasp a pullup bar with overhand grip, and slowly raise your legs up until you form a 90° angle.
Do the abs bicycle as well. ( 3 sets of 8-10 repetitions) remember your body has a muscular memory with time, it'll get used to your workouts and you'll do all of these like a pro

Do back hyper-extension or simply do the superman at home. position yourself laying down chest and head facing down, legs and arms straight. Slowly bring your legs and arms simultaneously as if you willing to touch the sealing. ( youtube it).That's how you'll become stronger. Believe in yourself kid.

It sounds kinda like you have no support holding down your feet?

Are you a male or female? Im a female & I have very limited arm strength, but really strong legs...which is typical for women. Ive never been able to do pull ups, curls..anything.

Yes it is completely normal, it’s not because of weak abs. If you are able to do sit-ups, but not curl-ups, it’s because of an issue with your back. I have the same issue. I can do 100 sit-ups, but like only 30 curl-ups. You might want to check with your doctor for confirmation.

See a doctor,

From your post you are 13.

There is no reason a healthy 105lb, 13 yr old girl or boy can't do a sit up (or curlup as you call it)

You most likely have a hip/lowerback/upper pelvic issue that needs attention

You should be able to comfortably do 10-30 situps especially if your post is accurate.

Pantz

Try sticking your feet under the couch because it holds your feet in place

I totally didnt understand what you were talking about, SIT UPS you mean!? I thought you meant doing chin lifts hanging from a pull up bar. Not being able to do sit ups, no not normal. Maybe u have a back problem.

you are a girly man,try working out with your boyfriend

Fatass