same thing applies for grinding too man.
it's like exercise. you have to keep exercising a little more intensed that what u are current used to to build up muscles.
a simple metaphor like the one on top when applied to drumming can help u achieve the same results too. if u find that you get tired easily doing all those more physical stuff like grinding or fast punk rock with all the tom rolls and stuff, keep repeating it and try to work past your fatigue.
u can't be a marathon runner if u just run 1km a day, can u?
