I am making my triathlon setup on my road bike and to align my kneecap with the end of my crank arm, I have to push my ISM saddle almost the whole way back. So it is not in the min max range anymore - any concerns or no problem? My weight is about 70kg if it matters.
I canāt speak for the structural analysis exactly, but at your weight, and with the general consideration that components have a certain additional Design Factor for Safety, you will probably be fine for saddle rail strength and loading.
Depending on the seat post you already have, you may be able to get one with more setback, that will allow a more centered rail location in the saddle clamps. Worth consideration if you plan on this being a long-term setup.
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thank you 
actually I bought a fast forward seat post for my road bike and increaded the frame from 26,8 to 27,2 to fit it. With my ism which came today I think the old one would have been better 
but if I get a fit you are right I will order a new seat post.
Thanks!
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Why do you want to align your kneecap with the end of the crank arm? You working to the plumb-bob from knee method of fitting?
I found it absolutely does not work for me and although it is a decent starting place for a first ever fit I canāt see why it is necessary.
If I have knee over spindle I would be riding a 58+ top-tube bike, at a 52ish frame stake (like Sagan - the only thing about me that is like Saganā¦). I am 5ā10" by the way.
Tried the Hogg method of finding the balance point (ride at 20 min power and put hands behind back, if you fall forwards move back - for me that is something like 8cm saddle setback) but prefer to be rotated slightly more forward than that around 5cm setback (Spesh Romin old style nose set 5cm behind middle of BB).
Can start with either but wouldnāt use either as a rule to be followed at all costs.
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@Boombang, The key element in fitting is to remember that it is HIGHLY individual. What works for one person could be terrible for another.
I also noted the stated fit comment about saddle and knee placement from the OP. I skipped commenting on it as that is a single data point and lacks any and all surrounding fit considerations that may well lead to that position being suitable for this rider.
Point being, I find it generally a bad idea to offer fitting advice without sufficient background from the person and their particular situation.
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Hey Chad, hope you donāt think I am trying to lead the OP a particular way. Just mentioned two relatively opposing views as examples for basing a fit on and noted neither worked for me. I was exceptionally careful in not saying do one or the other, just querying if they used a method I have never seen result in a great position on itās own without many other considerations.
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Thanks for mentioning your concerns about the fitting method - actually I was following this youtube video and double checked if I am in the suggested angle range here
Thought this might be a good starting point to avoid a professional bikefit. I am a student and I do not know if I will stick with it. So I thought to make one or two plans here on trainer road and if I still enjoy I will get a bikefit.
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I started a dedicated fit thread. Feel free to ask fit related questions there.
If you are using a Fast Forward post to change the seat angle of your bike so itās more appropriate for a TT position, following fitting advice for road bike setup is probably a bad idea. The reason for the steep seat angle is so you essentially rotate the whole human forwards about the bottom bracket. This allows you to get your front end down low and retain a reasonable hip angle, but obviously it also means that you are moving everything (including your knees) forwards.
Iād recommend getting a fit from a recognised bike fitter, but if you canāt do that, at least look at bike-fitting videos aimed at triathlon or TT bikes - the have different geometry compared to road bikes (and thatās what the Fast Forward post is trying to achieve).
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Iām running ISM Prologues on both bikes, both pushed back either to the āmaxā mark or past it and had no issues so far. Theyāve been like that for at least 3 years now and I weigh a lot more than you (>100kg at the moment). I got fit in that position by John Dennis who does Retul fits for a good number of pro teams and elite triathletes and he said its unlikely to be a problem, especially if the saddle rail clamp is a decent length so it still covers into the region between āmaxā and āminā.
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I did a Bike-Fitting at Staps last thursday. They help i.e. Tony Martin and Canyon Athletes like Patrick Lange with their fitting.
They told me that fitting with an knee plump line would be outdated, because fitting is so individual.
They try to reach a knee ankle of 140*, but for me 146 was better.
With no real bike fitting, Iād try to find a good saddle hight between 140 and 150 degree and then try over time which hip ankle feels good and which cockpit position I can hold for a long time comfortably.
Another red line could be that you donāt loose more than 5% FTP between your aero and your normal position.
Findling a good aero position is a neverending process. Try to be patient! 
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From what I understand - you should only use the plumb line/bob KOPS method as a yard stick to get you into the same range as a previous setup if you have something to go by.
If a professional bike fitter uses this method for anything more than that you should probably find a better bike fitter.
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I tried it but actually the seat is to far forward with it. To follow the triathlon fitting guide I have to bring my saddle more back. So I will use a normal seat post.
But speaking of the geometry the changed angle with the fast forward only pushes the seat forward or am I missing something? 
So I thought it is because of the small size of my bike and the ism saddle why I have to use a normal seat post to get better triathlon fit?
Typically, TT bikes or Tri bikes have steep seat angles (78 degrees or so). They tend to have aero posts with an inline clamp.
Most road bikes have 72 or 73 degree seat angles. The idea of the Fast Forward seatpost is that it uses the set-forward to change the effective seat angle to mimic the TT angle.
I know nothing about your bike or your position, and Iām not a professional fitter. Iām just trying to explain the theory of what the Fast Forward seatpost, why you might want to move forward for TTing, and how that would affect your saddle position and hence your knee position.
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exactly but only to get the saddle more forward - right
Sure, itās so you can get the saddle forward, because the theory is that itās easier to TT fast with your saddle a lot further forward than you would set it on the road. Hell, it makes enough difference that the UCI have a rule limiting how far forward you can put the saddle!
However, if you want your TT setup to be closer to your road setup, go for it. Donāt blindly follow KOPS though - it doesnāt really make sense for road bikes, but it definitely isnāt ideal for TT.