Your oblique muscles are the abdominal muscles on each side of your rectus abdominis. You have a set of both internal and external obliques. It's not uncommon for people to just focus on exercises that work their rectus abdominis -- the long paired muscle that runs down the center of your abdomen -- but in order to obtain a V-shaped physique, you must also exercise your obliques.
Standing Dumbbell Side Bend
For this exercise you will need a dumbbell with a moderate amount of weight. Hold a dumbbell in one hand at your side. Bend your waist to the opposite side until you feel a slight stretch and then bend to the other side. Repeat on both sides for a total of three sets. If you can do more than 15 reps, you are not using enough weight.
Captain's Chair Leg Lifts
A study commissioned by the American Council on Exercise discovered the Captain's Chair is the most effective exercise at activating the obliques. For this exercise you will need access to a Captain's Chair. Most full-service gyms have one. Stand in the Captain's Chair with your back flat against the back and your arms on the pads. Exhale as you slowly raise your legs toward your chest. Inhale as you slowly lower them. Perform a total of three sets to failure. The exercise is easiest to do with bent knees. You can increase the difficulty by keeping your legs straight.
An oblique crunch is very similar to a normal crunch except it places more emphasis on your obliques. To perform an oblique crunch, lie down on your back on an exercise mat with your knees raised, like you are going to do a normal crunch. Then tilt your knees to one side until they touch the mat, but keep your shoulders straight and against the mat. You should feel a slight stretch in your obliques. Once you are in this position, begin doing crunches as you normally would. Perform three sets to failure on each side.
Oblique Twist Hanging Leg Lift
For this exercise you will need a pullup bar or a sturdy beam you can hang from. Grab hold of the pullup bar and lift your feet off the ground so you are in a dead-hang position. Try to keep your arms fully extended. As you lift your knees up toward your chest, twist to one side. Twist to the other side on the next repetition. Perform three sets to failure.
Exercises that target the obliques can only do so much. It's important to participate in at least 150 to 300 minutes of moderately-intense aerobic exercise; along with at least two 20 minute sessions of strength training every week. The results of your spot exercises will only be evident if you commit to a regular exercise regimen and a healthy diet to keep your weight in check.