The elusive six-pack: everybody wants it, but few actually know how to achieve it. The core consists of nearly 35 muscles of the torso from back to front that are responsible for balance and stability.

If you're spending hours in the gym crunching away to no avail, there's a good chance you're falling victim to a common abdominal training mistake. With a few tweaks to your training and lifestyle, you can shave minutes, if not, hours from the total weekly time you spend training your abdominals and finally achieve a more flat and defined midsection with more effective work.

You do too many reps

Thinking the abdominals are the only muscles of the core, people often perform too many repetitions of isolated abs exercises. Remember that other movements like squats, lunges and overhead presses perform double-duty to work the entire core. Abdominal training happens before you hit the mat. Make compound movements a regular part of your fitness program. Then, 15 minutes of abdominal-only exercises at the end of a workout should be all you need. Think of the abs like you do other muscles and focus on three sets of no more than three exercises.

You're not using any resistance

Like any muscle, the abdominals don't tone, they grow and they do this best and fastest when they're worked with resistance. The most effective way to grow and strengthen any muscle group, including the abdominals, is to progressively overload them by adding more weight as your body adapts to the demands of the current routine. Add weight to some of your abs movements to create a combination of weighted and weight free exercises.

You only attack them from one angle

One reason people only do crunches to strengthen their abs is because with just one fluid movement, they're easy to do for long periods of time. However, because a traditional crunch only works abs in one direction, it's one of the least effective abdominal exercises. The muscle fibers of the abdominal wall run in many directions so train your abdominals in more than one direction with exercises like windshield wipers, bicycle crunches and cross-body mountain climbers, planks, side planks and twists.

Your diet needs an overhaul

It's the age-old question; are abs made in the kitchen or the gym? You can work your abs for days (though I hope after reading this article you'll discover you don't need to) but if you're not eating a healthy diet, you won't see results. Like any other muscle group, abdominals aren't visible if they're covered by fat from poor eating habits.

You train your abs every day

Abdominals are commonly over trained. You should aim to work the core two to three times per week with a variety of exercises at different angles. The majority of your workout should train the rest of your body with compound movements that also work the core. Focus on abdominal-specific exercises at the end of the workout.

Brian Maher is the owner of Philly Personal Training, a Philadelphia-based studio offering 1-on-1 personal training, physical therapy, and nutrition counseling. 

Read more Sports Doc for Sports Medicine and Fitness.