My trainer suggested me to do 3 days upper abs, external obliques and 3 days lower abs, internal obliques alternatively in a week. Is it a good approach to burn fat and get abs quickly?
For getting abs? Sure.
For burning fat? No.
Doing ab workouts doesn't do much in the way of burning fat. Fat burning happens when you consume less calories than you spend over any given period of time. As such, this is something that is best accomplished in the kitchen.
For most people, the size of the abs isn't the problem. It's the layer of fat on top of it. So unless you have really underdeveloped abs, doing a lot of ab work is mostly overkill.
But with that said, abs are muscles like any other, and will react to hypertrophy like any other. But since it's a rather small muscle group, it's very limited in how much volume you can hope to gain.
I'm very confident in saying that you will have a lot more success getting a proper workout program with compound lifts, which will invariably strengthen your entire core, including the abs.
Anatomically there is no "lower abs", you have the rectus abdomonis which is the six pack. This muscle looks like it may contain specific lower, middle and upper parts but that's not true. So no, you don't need to split your ab training unto different days. Also your obliques will be trained when doing exercises like crunches so you don't necessarily need to train them specifically either.
We all have abs the problem is the fat. So reduce that fat by eating less than your calorie maintenance level but not too much or you will lose more muscles in the process. So the solution to your question is:
- Get your calorie maintenance level.
- Then eat little less than that and if you see you are losing weight then you are doing it right but don't be unrealistic 0.5-1.5lbs is fine per week especially if you're looking to keep those precious muscles.
Again, if your goal is to show that abs the key is DIET and not so much on the workout. I've done 100 sit-ups 3 times a week for 3 months and I didn't even look different from the first time I lifted weights and all thanks to my instructor. It was a case of the blind leading the blind. So do your research about diet and always be skeptic about what other people tell you and match it with scientific evidence there are a lot of resources available in this day and age!