Recently I came across a website where was promoted, that if you are serious about your core strength you should start to do sit ups.
Actually the aim was to be able to do 200 consecutive sit ups.
Where being able to do 200 sit ups is something admirable and takes some work surely, it does not really mean that your abs and core are amazingly strong.
It just means that you are able to do 200 repetitions, nothing more.
Well how do you get stronger abs and core if not by being able to do hundreds of sit ups.
Resistance training is the key.
I'm not saying that a man or a woman who's able to do 200 repetitions doesn't have strong core and abs, it much depends on the upper body weight.
For slim person it does mean that there doesn't need to be that much strength in the core to be able to do those 200 consecutive repetitions.
Let me clarify, to be able to do one sit-up takes some amount of strength, to be able to do 100 sit-up takes a little more strength but much more muscle endurance.
So this is the point here, training and doing hundreds of repetitions without resistance only makes your muscles more endurable.
This will mean flatter stomach and better abs, but not strong.
Stronger abs can be achieved by doing different ab exercises and using weights or something else as resistance.
If you want to get stronger core, sit ups is a nice exercise for that and especially incline bench sit ups are the thing that works.
There are plenty of other exercises as well like straight leg lifts, different crunches etc.
The main thing is to use resistance and to do 15 - 20 repetition sets at max.
There is no need to do longer sets, just make sure that your abs are really working out every time you exercise.
All in all, the number of sit ups you are able to do doesn't necessarily mean you have really strong abs, it just means your abs are in shape.
You should do different resistance ab exercises to really get stronger abs.