I have a polar 625x and I'm doing a sprint on Sun.

1) Has anyone tried to use a multisport during a race?
2) How do you switch modes, i.e. from cycling to running? Mine does not seem to have a way to keep the same workout but use different modes.
3) Or do you set it for HR and leave it at that?
4) Do you wear it for the swim?

I wouldn't bother for a sprint. Its all out the whole way. I don't need a HRM to tell me I'm working my butt off.

If you do, wear it the whole race. Are you wearing a top or wetsuit on the swim? This would keep it from sliding down. Just show HR. Having an out of zone alarm beep the whole race is like chinese water torture.

I wore a heartrate monitor at my first tri. I found it distracting and it caused me to hold back too much during the race. I'd look down and see my HR at 160 and back off. I know now that I can hold 160 during a race for a pretty long time and if I back off I am giving up time.

How do you switch modes, i.e. from cycling to running? Mine does not seem to have a way to keep the same workout but use different modes.

I agree that for a sprint it is not necessary - even for an Olympic it's too short for me to worry about. I do however - use mine in training every day as it is an easy to log my daily training to my home PC. I also use it in marathons, 1/2 IM's and IM's to keep me on pace. In a marathon my HR tends to just stay in the 165 - 170 range. My max HR is 196 (at age 46) and I have not seen over 200 in 3+ years. I do set a max and min range and mine will beep at me if my HR exceeds 175.

I have a 720i and never had an issue in the bike to run but I have heard the same issue about the 625x. I do use mine in the swim, but never look at it until about mile 15 or so on the bike in a 1/2 IM or like mile 13 in a marathon (where the race really starts for me).

I can't help you with how to switch the modes--call the company or a local tri shop for technical assistance. I think you should wear it throughout the race (again, provide you are wearing a wet suit or tri top). Even if you never look at it during a race, it would be useful to know what your heart rate vs. perceived exertion levels are. Knowing that 175 bpm is your sprint race-pace heart rate on the run will help you know what is too high when you do longer races. I wear mine for every workout. If my HR approaches 180 on the run, I know I will be hitting a wall in a couple miles if I don't back off.

Thanks. No wetsuits, so maybe I'll just do w/o.

I bought a HRM once thinking it would be good to try. I found the chest strap to be extremely annoying, period. Eventually the battery died, I tried to replace it, and now my HRM doesn't turn on amymore....

Anyway, would I wear it in a race? Maybe if I was comfortable with it and knew exactly what I was doing and what my goal was. When I did my first sprint though a couple weeks ago all I could think about was how many people I had to pass to catch back up after doing so poorly in the swim. Pushed about as hard as I could on the bike, and on the run I was a little slower than it could have been, but I picked it up over time. I think a HRM would have only told me that I was working hard, which I knew already.