Well generally it will be a positive impact (Of course this generally depends on what the "Physical activity" is, it is generally good, reason being while exercising causes the brain to release endorphin's, as well as helping relax muscles and relieve physical tension, which can greatly help with stress.
The answer is A. millileters
B. As a cross country runner its very important to warm up before I run a marathon or a long distance run or just any run in general its always something I have to do. If your do the strenuous activity without warming up your muscles will be tight and will sort of go into shock. By warming up you are releasing tension in your muscles and ligaments and getting you blood flowing. In my experience I didn't warmup once before a half marathon and had to stop about a mile in because I tore my hamstring. It strained it right off the bat and kept getting worse just because I forgot to stretch! I hope this helps!
