Abdominal exercises
Especially your abdominal muscles. You can probably start more intense cardio after 6 weeks but I would definitely wait 8 weeks before starting ab work and also when you do start, do not start with situps and crunches, start with planks and exercises that work your entire core. There are about 10 different plank exercises you could do for 2 weeks before you start in on crunches or situps.