Lie on your back with knees bent and feet flat on the floor. Hold a kettlebell with both hands at your chest (or extended slightly upward depending on variation). Brace your core and begin sitting up by curling your torso forward, lifting your shoulders off the ground and continuing until you reach a tall seated position. Pause briefly at the top, keeping the kettlebell controlled and close to your body. Slowly lower back down under control, one vertebra at a time, keeping tension in your abs throughout the descent. Repeat for reps.
Log your kettlebell sit up sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.