It could be seen alike power training, it's a matter of keeping doing it - training. Knee problems tend to begin when having ceased awhile and restart.
Also, if it's cold, try to avoid having to push hard before warmed up.
Pants that reach to beyond knees (three quarter pants or how do they call it?) are a good trade off between ventilation and knee temperature management. And on fixies they avoid pants getting caught between chain and chainring, a potential disastrous event.