I've often read and heard that you can only build more muscle-mass (get stronger), if you continuously increase the resistance weights (e.g. [here][1]).

But for me, it's the case that I'm often not able to increase the resistance. I have to take the same resistance weight as before (regarding training over several weeks) because this is all I can do.

Is it really correct that my body won't build more muscle-mass because it needs increasing resistance? I mean, this resistance is the limit for me - so why should a constant weight be too little?

**This is my current schedule for training:**

Monday:

 - 2 exercises x 3 sets x 8-12 reps: back (trapezius etc)
 - 2 exercises x 3 sets x 8-12 reps: biceps (brachii)
 - 2 exercises x 3 sets x 16-20 reps: abs (abdominal)

Wednesday:

 - 2 exercises x 3 sets x 8-12 reps: chest (pectoralis etc)
 - 2 exercises x 3 sets x 8-12 reps: shoulders (deltoid etc)
 - 2 exercises x 3 sets x 8-12 reps: triceps (brachii)

Friday:

 - see Monday

Monday (next week):

 - see Wednesday (start this week with the second part now)

**Someone told me to change the plan to the following:**

Monday:

 - 2 exercises x 3 sets x 8-12 reps: back (trapezius etc)
 - 1 exercise x 3 sets x 20-30 reps: abs (abdominal)

Wednesday:

 - 2 exercises x 3 sets x 8-12 reps: chest (pectoralis etc)
 - 1 exercise x 3 sets x 20-30 reps: abs (abdominal)

Friday:

 - 2 exercises x 2 sets x 8-12 reps: biceps (brachii)
 - 2 exercises x 2 sets x 8-12 reps: triceps (brachii)
 - 2 exercises x 2 sets x 8-12 reps: shoulders (deltoid etc)
 - 1 exercise x 3 sets x 20-30 reps: abs (abdominal)

Is this a better schedule?

**Stretching**

I must admit that I've never done stretching as a part of my fitness training. I know this was a mistake. But could this even be the cause for my lack of strength?

  [1]: http://fitness.stackexchange.com/questions/959/to-count-or-not-to-count