Running a Sprint Tri at the gym?

Before I did my first tri ever I did this - but I actually simulated the distances.  swam 400, biked 15 and ran 3.1, all indoors.  I did it about a month in advance to my race - just to prove to myself that I was able to complete the whole thing and put any DNF thoughts to bed.  It was gratifying. 

I did the same thing with the actual distances at the Y a couple of times during my training before my first tri - ironically the NJ State Sprint that you last did.  While I cannot say whether it is good to do every week as part of training, I did feel confident for my first that I would be able to complete the entire race.  I would think that if you are doing it in the off season and not trying to do actual distances that it would not hurt, but again, I am still very new to the sport.

Me too!  Before I had any clue of BT or training, I figured just "doing it" was good training.  I did TONS of simulated triathlons, maybe once a week.

However, when I started training for my first race, I realized there was probably a little better method to get ready and started following a plan.

BUT, I was interested to see that some IM plans, even here on BT, have you doing all three disciplines in one day, no reason to think they couldn't be done back to back (to back)...

great idea...I can see doing that perhaps every 3 weeks or so.  Every week not so much.  It's not that I think you will get hurt...but if you go all out on those you need more recovery for other workouts. 

I do like the idea though...this would be great on a cold winter day when it's in the 50's outside .

I do this all the time 2-3 time/month.  My indoor tri is a 1000-1500 yrd TT, 45 min spin class going at full bore followed by a 4 mile run at race pace and a 1-2% incline on the dreadmill.  Because transition from swim to bike is a bit slow it is not truly a tri IMO, but it shakes up the workout routine and knocks out a workout in each sport.  I usually do these on a day I know I will eat like a pig (like last saturday) and follow up the next day with a recover workout.  I'll usually take a gel or shot block before the bike and lots of water on the bike and run.