system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Would the human body adjust to higher gravity, extreme temperatures through slow but increased training

Disclaimer: I've seen similar questions. but they've been archived already(and not completely the same. If I started at 1.5x gravity and went to 2x then 3x etc. As in Goku training for Namek but on a much slower scale. Would our bones grow denser? Would our bodies just  crush at some point? In the same rate if we trained for extreme temperatures. For instance, start at 100 go to 105, 110, 115, 120 etc. Would we adapt or reach a threshold limit?
gpt
Temperature is a lot harder! We have biological processes such as enzymes which will not change no matter how hard you train. Above certain temperatures many biochemical processes will slow and eventually cease. 

Muscles and bones however do respond to stress by building and strengthening tissue and bone. Lung capacity, red blood cell count wouls probably also increase under such conditions. What the upper limit of gravity a human could survive in is unknown.