system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why are we shaking when we try to lift more weights?
gpt
It's fatigue.  At a certain point when lifting weights your muscles will  be fatigued from either lifting weights again and again and again or you'll lift something that's just on the cusp of your ability to lift.  At this point your muscles will start to fail.  They'll contract and then stop contracting and then contract again.  This causes shaking as when they stop contracting they're not working.