After a years research, stretching is not as beficial for muscle weight training than it is for aerobic training such as footbag.
Stretching helps to increase blood flow around the body which helps transport oxygen better which then means lactic acid can be broken down a lot easier.
Weight training does not require stretching as a warm up because an elongated muscle during weight training may decrease the strength, whereas if the muscle wasnt stretched u can see it being more compacted and therefore allows the muscle to work more uniformly and tightly i guess..