Single Leg Raise on Bench. How-to, proper form and tips

An easy approach for the L Sit position, strengthening one leg at a time.
Video demonstration
(excerpt from 'Best Exercises To Increase L Sit HOLD'
by FitnessFAQs)
How to and step by step instructions:
- Sit down on a bench, preferably lower than your knee-to-foot distance.
- Keep your back straight, in vertical position or even in a slightly forward bend.
- Raise one leg horizontally and hold it in that position.
- Count the number of seconds you can hold.
Hints & tips:
- Use a lower bench for a harder exercise.
- Keep your back vertical or a lithe forward, not backward.
Benefits:
- Improves posture.
- Strengthen quads and hamstrings.
Counting & gamification:
- Count accumulated seconds in a session.
Muscles worked and body parts involved:

Primary muscles: Abs, Quads
Secondary muscles: Hip Flexor, Hamstring
Other names
The exercise can be found with other names. Examples are:
- Single Leg Raise on Bench
- Straight Single Leg Raise on Bench
- Single Leg Lift on Bench
- Single Leg Raise on Chair