The toes-to-bar is a calisthenics exercise that primarily targets the abs and to a lesser degree also targets the groin, lower back, hamstrings, and hip flexors.

Muscle group: Abdominal

Steps

1. Initiate a kip by swinging feet front and back, and follow swing motion through to hips and then shoulders
2. The body should bow from global extension to global flexion
3. At the apex of the "from" portion of the swing initiate an aggressive "toes to bar"
4. At the apex of the from portion of the swing initiate aggressive toes to bar
5. Once toes meet the bar (or pass the arms) explode quickly out of the piked position, sending toes back down directly into a hollow body position
6. Don't allow feet to come behind you or you will lose the timing and tension needed on the system to link them efficiently
7. Keep the head in during entire movement

Tips

Use the momentum of bringing your feet down and back to help swing your feet back up on the next rep.
Try to develop a good rhythm and stay fluid in your movements.
You can also keep a narrow grip on the bar and swing your feet wide,
Ideal situation would be toes passing through the arms with legs together

All exercises