The fronts of your thighs and hips can become very tight if you perform a lot of lunges and squats or if you run or hike. Here's a great way to increase the flexibility in those areas while working on your core strength.
Kneel on a padded level surface with your hands under your shoulders and your knees under your hips. Raise your left knee off the floor behind you, lifting your left heel to the ceiling. Keep your abdominals pulled in to support your spine.