My leg lifts are done as so:
Lie on the ground flat on your back, legs straight and toes pointed. You can put your hands under the small of your back if you like for support (the motion can cause some discomfort there, but your hands or even a really small pillow will solve that).
Keeping your knees straight, slowly lift your legs (I do a slow 6 count - probably about 10-12 seconds) at your hips until they are nearly straight up in the air. Keep your toes pointed.
Still keeping your knees straight and your toes pointed, slowly bring your legs back down (I use the same 6 count) until your heels are about an inch off the ground (have someone at your feet to tell you when you reach that for the first few times you do this, until you can just feel when you're there). Then repeat the lift.
Do as many reps as you can/feel you should. On the last one, when you bring your legs back down, stop and hold with your heels that 1 inch off the floor for 30 to 45 seconds before you finally release and relax.
My fencing coach actually called these "crunches", because they work your abs like you wouldn't believe (with no other ab-specific exercises at all, I had a well-defined 6-pack!), but this time around I plan on doing some "real" crunches to help with getting my heart rate up during my routine, so I needed to pick a different name for this exercise.
You're absolutely right that a heavier person will just naturally develop more muscle to carry that weight. However, I wouldn't expect that so much in the arms, and any such muscle gain in the arms I would think would be more than offset by the increased body mass. I'm certainly nowhere near my peak, but neither am I at my worst in terms of number of push-ups I can do (when I started fencing, I was a skinny little high schooler who could only manage 5 or so push-ups period).
Lie on the ground flat on your back, legs straight and toes pointed. You can put your hands under the small of your back if you like for support (the motion can cause some discomfort there, but your hands or even a really small pillow will solve that).
Keeping your knees straight, slowly lift your legs (I do a slow 6 count - probably about 10-12 seconds) at your hips until they are nearly straight up in the air. Keep your toes pointed.
Still keeping your knees straight and your toes pointed, slowly bring your legs back down (I use the same 6 count) until your heels are about an inch off the ground (have someone at your feet to tell you when you reach that for the first few times you do this, until you can just feel when you're there). Then repeat the lift.
Do as many reps as you can/feel you should. On the last one, when you bring your legs back down, stop and hold with your heels that 1 inch off the floor for 30 to 45 seconds before you finally release and relax.
My fencing coach actually called these "crunches", because they work your abs like you wouldn't believe (with no other ab-specific exercises at all, I had a well-defined 6-pack!), but this time around I plan on doing some "real" crunches to help with getting my heart rate up during my routine, so I needed to pick a different name for this exercise.
You're absolutely right that a heavier person will just naturally develop more muscle to carry that weight. However, I wouldn't expect that so much in the arms, and any such muscle gain in the arms I would think would be more than offset by the increased body mass. I'm certainly nowhere near my peak, but neither am I at my worst in terms of number of push-ups I can do (when I started fencing, I was a skinny little high schooler who could only manage 5 or so push-ups period).