I'm 14 years old, and throughout the multiple tests we've had to do in gym, I am never able to do a curl up without automatic form break. My lower back doesn't go up and my arms move causing the form-break. I am also not very athletic, I don't like doing exercise but I can do the average amount of push-ups and pacers, etc. Is it because I don't have core strength? Or because of physics? I'm 4'11 and I weigh 103lbs. Please help!
Don't get discouraged, repetition is the only way to improve.
Try putting your hands behind your head and with your legs bent at a 90-degree angle and your feet firmly on the ground as you begin to go up try pushing down with on your heels.
Alternative exercises such as planks or hip lifts could be beneficial for improving your core strength.