I only have and need one motivational quote:
Stop thinking! Thinking invites distraction. With a clear mind, no hurdles arise and you can just "be". With no thinking, there is no "I don't feel like it today", or "I can't do it". Thinking breeds aversion, so stop thinking. Just get up, go to the gym, and lift. Don't think about it. You know proper form, so just do it. You know the benefits, so just do it. Discard thinking and you discard your obstacles.
I usually just say "stop thinking and go do it". The above is the full version. I created this quote based on my spiritual training, inspired by the Buddha and my other Dhamma teachers.