Once you are confident generating and maintaining tension with bent knees. We can advance by straightening our legs - beginning with an upward angle.
Begin with knees bent, arms extended forwards and raising the shoulders and upper back off the floor. Keep reaching forwards and maintain tension, as you extend the legs at an upward angle.
You may hold for the required time in this position.
As you continue building strength, lower the legs closer to the floor to increase difficulty.
Try to progress your leg position session to session, but do not allow intensity to drop. We need to keep the core shortened and shoulders elevated.
Anytime your form breaks down, rest, and reset, there is not point increasing your hold with poor form. You will only progress in strength by striving for maximum total body tension.