Six-pack abs — everyone wants them, but only some know the best ways to get them. Contrary to popular belief, it’s not just about staying loyal to the standard crunches. The secret to the six-pack is more complex and incorporates a healthful diet to reduce fat, cardio to get lean and let those abs show, and functional exercises that consistently engage the core muscles, which also involve the back.

Those key abdominal muscle groups include the rectus abdominis (the ones along the front that comprise the six-pack); the internal and external obliques that flank the rectus abdominis and help the trunk rotate; and the deep muscle layer called the transversus abdominis that lends stability to the pelvis.

Three Southern California personal trainers offer their core ab thoughts.

Jon Baraglia

National director of personal training development for Bally Total Fitness:

The truth about abs is that you have a layer of fat between the skin and the muscle, and it doesn’t matter how many crunches you do: If you don’t cut down that layer of fat, you’ll never see your abs. You have to do exercises that are high in caloric expenditures — compound joint movements like squats, lunges, lower body exercises that recruit a lot of muscle fibers because they’re incorporating more than one muscle group. The overall result is that you burn more calories.

There is no such thing as spot reduction. You’re not going to lose fat in your midsection if all you’re doing is crunches. Crunches burn very few calories compared with other things you can do.

People who aren’t overweight (but still have that layer of fat) can bump up the intensity of their workouts. Also, a lot of people like to shy away from resistance training and focus on cardio, but resistance training increases lean muscle mass, and you burn more calories to maintain that lean muscle mass, so your body’s daily caloric expenditure increases.

One great exercise is a simple bicycle crunch — alternate bringing your elbow to the opposite knee. That rotation is good for your abs and obliques. Another good one is the captain’s chair (an exercise using equipment that looks like a chair with no seat; the body is supported by the arms as the legs come up to the chest). Your lower body is unstable, so when you bring your knees up to your chest, you have to call on all the muscles in the core. In the advanced version, the legs come straight up (at a 90-degree angle).

Jana King

Personal trainer and abdominals group fitness instructor, Equinox, Santa Monica:

Practicing good posture throughout the day is really going to give you a flat stomach. I tell my clients that no matter what they’re doing in the gym, they should suck in their stomach, imagining that they’re bringing their belly button to their spine. If they’re on the mat or on a machine, like the knee extension machine, they should bring their lower back to the mat or make sure it’s in contact with the seat. Even when I’m driving I’ll sit up straight and pull my stomach in. It can be more effective than five minutes of abs, because you’re constantly activating those muscles.

I also like to do some isolation exercises — isometric holds, like planks, to develop the deep-tissue muscles such as the transverse abdominis and the internal and external obliques. That helps support your posture and develops the muscles that keep the stomach flat.

Developing back muscles is important too. If you only work on your abs, then your lower back won’t be strong enough to help you sit up straight. If you don’t work them out, you’ll start to bring your body forward, rather than maintain that good posture. To do a back extension, lie down on your stomach and raise your hands and feet so that your stomach is the only thing touching the ground.

Anthony Slater

Head performance specialist at Core Performance Center, Santa Monica:

We train with the concept of pillar strength — that encompasses the six-pack and a little beyond. It’s the foundation for movement and includes the hips, torso and shoulders. … We’re creating this pillar that allows you to train more, to withstand more volume and intensity, so that you’ll lose weight and change your body composition.

One exercise is a side bridge that adds a variation with a cable row. You’re (on your side) with your elbow under your shoulder, forming a bridge from the side of your foot, which is on the ground, to your elbow. The legs are stacked and the posture is long. You have a cable in your top hand, and you row the weight to your side, like a dumbbell row, pulling with your shoulder blade. As you pull, it creates a torque against your body, which should stay strong. This promotes stability in the hip and the shoulder blade and the torso, which includes the rectus abdominis and obliques. You have to think about maintaining that pillar posture — the focus is on the quality of the movement. But in order to maintain that quality, the abs have to be contributing, stabilizing the body.

The exercise can be (made easier) by coming down to your knees instead of resting on your feet. Or, instead of having the legs stacked, add a little stability by having one leg forward and the other back. To add difficulty, lift the top leg.