continuous running and HIIT...

i know that longer distance running makes you slower and lactic acid work causes conversion to slowtwitch fibres, but how much of each of the above is enough to produce a negative effect?

It’s in the soccer season, and our coach makes us go on intense 3200m continuous jogs once/week, and HIIT type running once week where we sprint 30 sec, rest 1 min and repeat 6-8 times… now i was wondering if these two sessions together or done alone (ie maybe the 3200 m run once week) would be ENOUGH to cause any negative gains in speed?

Are you experiencing some decline in speed qualities?
And why the hell would your coah try to fix “endurance” during a season while the actuall game play will cover this issue? I would pursuit specific speed qualities, tactics, strength & power and use tempo or easy fartlek for recovery day after the game or something… Maybe 1-2 practice of aerobic games (please take a look at Bangsbo “Fitness training for soccer-scientific approach”).
What you are currently doing is not specific and if even done, it should be done before season!

well our season hasn’ actually started yet… (there was some delay due to problems with the league) so this is still preseason.