You can say the same thing for literally anything in life. Studying for college exams for example is a grueling situation that will leave you utterly exhausted both mentally and physically even if you eat and rest properly and all you are doing is note taking and flipping pages. You are confusing fortitude with strenuous physical activity.A few games of pool is not physically demanding but ever been to a 3 day tournament and play on the third day, it's grueling and the folks that do it week in and week out are, IMHO, an athlete. I've in fairly decent shape and it wears me out playing all day.