Also known as leg raises, which is going to mainly be working the hip flexor muscles (Iliacus, Psoas Major, Rectus Femoris & Sartorius Muscles). The main hip flexor muscle involved with this movement is the iliacus.
This blog shows the neutral level for this exercise, but remember leg lifts can be modified for your own intensity.
How To Perform A Leg Lift:
1. Lie on your back with your arms out to the side of your body.
2. Lift both legs up to the ceiling straight above your hips. Your knees can have a slight bend.
3. Tuck the belly button into your spine and tighten your abs, placing the small of your back up against the ground.
4. With control, keeping the legs straight, lower both legs towards the ground until the heels hover about 6 inches off the ground.
5. Lift the legs back up towards the ceiling and repeat!
6. Which ever way you need to, Just breath for now ;)
Now, you may feel some strain or burn in the thighs, this is normal!
The reason for that is because of the hip flexors activating. The hip flexors are the muscles that cross the hip that connect the thigh muscles to the core muscles, to say simply. Your thighs will most likely feel the burn as you lower and raise your legs because of the hip flexor, Sartorius
Now, to amp up your game with this exercise!
1. Attach weights to your ankles
2. Hold a dumbbell between your ankles
3. Bring your hands above your head
4. Hold a stability ball between your ankles
Usually your body weight is just enough to get the burn your looking for. Although sometimes the main exercise is just a bit too difficult for the core strength you are at currently, so here are some modifications that you can start with as well:
1. Lowering just one leg at a time. You will still start with both legs in the air, only lowering and raising one leg at a time, alternating legs.
2. Bend your knees. Keeping your knees bent will take off additional strain on your core muscles and lower back.
I personally started with 3 sets of 12 repetitions twice a week. Once that became pretty simple, I increased my repetitions to 20, then 30, then 40! Eventually, I was able to complete 100 repetitions on one set non-stop, but remember this was over a course of a year! It does not happen suddenly! Keep working at it little by little, always pushing yourself a tad bit but not too far to injure, & have Fun!