How to Measure Interval Training Intensity?

What kind of gadget do you need? Is it different for 1) cycling, 2) running, and 3) swimming?

The other question is: Do you know a gadget that beeps after a user-set time (like 1min) and again after 30 seconds, etc.

i like to start a cycling, running and swimming Interval Training cycle/program, but i don't know how to Measure Interval Training Intensity.

I use a wristwatch.

yeah, polar wristwatches are quite good and can be used in the pool too

Just some of them can give you your heart frequency under water (swimming).

You can have the specifics in their website: polar.fi

I own the F60 (works under water) and the RS800CX (it does not give you your heart frequency under water but is great for running and cycling)

Weird, I've always wanted to measure the intensity of my cardio workouts... and lucky for you I have a way. Peter Sisco has the power factor. Well I have something called (ready for this shocker?) ... the INTENSITY FACTOR.

Use this equation per interval:
IF = 2s * t

s= speed in mph or kmh
t= time in minutes

the integer that this equation spits out is just a number. The point is the BEAT your IF score everytime you jog/run/bike/swim

To get your avg swim speed you can just use the good v=d/t equation since you know exactly how big the pool is.

Also, if you notice the equation favors an increase in speed vs an increase in time, this is because the old a$$ dogma of low intensity and high duration to lose fat is B.S. Since coming up with this method over the past few months, it's been IMMENSLY successful at kicking my butt every workout and delivering kick-ass results. I'm still fine-tuning this method, and will release a full blown article on my blog in the future.

For now, step it up and use this. Tracking is EVERYTHING... if you don't track, you're aiming blind and wasting your time.

yeah you do need to track loads, I keep a little exercise diary where i give myself scores out of ten on how i felt during and after + how i felt the session went + info like max heart and average heart etc. I find it really useful and would advise others to