There’s nothing like a lean waistline to make a person look and feel fit. Having well defined abdominal and oblique muscles is one of the more common goals of those beginning and maintaining a fitness training program,

But, there are common errors, both mental and physical, when working toward a lean waistline. Here are the top five mistakes:

1. Not Focusing on Diet.

That’s right, you can’t work your waistline to death and expect abs and obliques to come popping through 2 inches of fat. Not going to happen. So, yes, in the end, your midsection and core are going to be a reflection of your diet. You can increase the strength and musculature of the abdominals and oblique muscles until the cows come home, but it is only after your body fat decreases that you will expose your success.

Strategy: Work to slowly eliminate simple carbs and sugars from your diet. Understand the importance of having some fats in your diet, but cut out those that are unnecessary, such as saturated fats – which are generally solid at room temperature – and those found in creams and sauces. Be especially mindful of the caloric density of foods and watch for those foods and drinks that add calories without nutritive value (i.e., check out the calories in your favorite alcoholic drink).

2. Doing the Wrong Exercises.

Your abdominals and oblique muscles are put to work when your spine flexes. If you tuck your chin to your chest and slowly roll your spine forward toward your pelvis you’ll see that spinal flexion only occurs in a limited range. However, if you want to come all the way up (as in a standard sit-up), you will need to perform hip flexion.

Problem is, hip flexion, well, works the hip flexors – not the muscles in your waistline. And making matters worse, if your abs are weak, your hip flexors will take over earlier in the movement. Here’s how to make your movements concentrate on the muscles surrounding your waistline.

Strategy: Make sure your movements involve spinal flexion. That means you should perform “crunches.” Yes, it is a very short range of motion, but that is all your abs do. Certainly, there is nothing wrong with completing a “sit-up” with hip flexion as long as the crunch portion involves controlled spinal flexion. Tip: Assess where you are fatiguing; is it in the abs or hip flexors? Good, focused crunches ought to tax your abs first. Oh, and whatever you do, avoid the abdominal machines in the gym. When the average person pulls those handles downward they stay in lordosis and do not flex the spine at all.

Bring your oblique muscles in with a twist. However, many people make the mistake of completing a crunch (or sit-up) and then, at the top, twist. That does nothing at the oblique muscles have no resistance at the top of the motion. Instead, twist on the way up. Side bends with weight also work to bring in the oblique muscles, but make certain the bend is directly to the side and not to the front or back.

3. Not Incorporating Planks.

It can become easy to forget the importance of isometric work (where your muscles are contracting but not shortening or lengthening) when training for a lean waistline. The reason isometric work is so relevant to waistline training is because your core muscles are always working to maintain posture and fight gravity. In other words, your core muscles are working isometrically all the time. And planks are a perfect way for you to train your core in the same way they are designed to work.

Strategy:  Begin adding planks to your training routine, preferably at the end. Start with forearm planks, where you are on your forearms and toes. Make sure you keep your hips in line with your body; don’t raise or drop your butt out of a straight line between your heels and shoulders. See how long you can hold it. One minute is a good starting goal. Then, increase the time slowly. You will soon see that planks are not the easy rest some people assume they are. Side planks, where you are turned to the side and holding your body up with one arm, are more advanced but a great way to bring in the obliques.

4. Forgetting About Pelvic Tilts.

Want to hit your lower abs? Crunches won’t do it. Why? Because you lower spine (behind your lower abs) can’t flex. And why not? Because your pelvis is in the way. However, you can cause the lower ab muscles to contract along with the pelvic floor when you perform pelvic tilts.

Strategy:  Think of this as a reverse crunch. Lie with your back on the floor in a neutral position with your legs bent and toes facing forward. Pull your belly button in toward your spine, pushing your pelvis up toward the ceiling. Tighten your gluteus and hip muscles as you tilt your pelvis forward. Hold for 5-10 seconds. Perform 5 sets of 15 reps.

5. Not Stretching the Lower Back.

The muscles of your core and midsection work together with your lower back. Your spine flexes, and therefore your abs and obliques work, only to the extent your lumbar back allows. A tight lumbar region means a limited ability to train the abs and obliques fully. Many people make the mistake of ignoring their lower back in their training and then can’t understand why their core and waistline isn’t responding to training.

Strategy:  Six times per day (yes, six), take 5 minutes and perform a lower back stretch that involves your hamstrings. Start with the knee-to-chest stretch. Hold for at least 30 seconds. Alternate that with the “child pose,” where you are on your knees with your face down and reaching your arms forward to the floor in front of you, and the supine twist, in which you are on your back with your arms to the sides, twisting at your hips (the leg that twists over the other should be bent at the knee). I promise if you do this six times per day, not only will you have more effective core training, but you will see any lower back pain slowly disappear.