THE L TRAIN

The L-Sit is a staple movement in the gymnastics world.  While it is primarily a core exercise, there is also a mobility component.  If hamstrings are tight it will require more core (abs/hip flexor) engagement to keep the legs up.  Additionally, a strong support position makes this exercise more manageable.  Elbows locked and externally rotated.  Ideally, the exercise should have shoulders leaning back / hips slightly forward which will engage rear delts and triceps more than you think.  If your anterior felt is working overtime, you are probably leaning too far forward.  

For this workout, break up into manageable chunks from the start.  Obviously, limiting rest will be key but once fatigue sets in it will be hard to maintain position so be smart about your rest time.  Turning over into seal position during your rest to help open abs and hip flexors will help recover between hold times. -Dave Durante

The L Train
2 min L-Sit Hold:
Accumulate hold in the shortest time possible. 
Scale: Tuck Hold