*Make sure you stretch really well first. Loosen up, you'll need it.
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5 minute walk/easy jog warm-up
3 miles @ 5k pace
5 minute walk/easy recovery
3 miles @ 5k pace
5 minute walk/easy recovery
1 mile as hard as you can w/out puking
5 minute recovery jog/cool down
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-enjoy

Yup, if you can do seven miles at 5K pace plus 20 minutesof recovery in 45 minutes, you would be one fast tri_newbie!

I'd just keep it simple and use the inverval setting on most treadmills. Mine does 2 minute intervals. You can use the interval speed calculator on the McMillan site to get your target paces based on a recent 5K time, warm up for 5, do your 2 on 2 off intervals, cool down for 5 and you're good.

Do longer intervals, half mile hard, mile or so moderate recovery pace, rinse and repeat. Half mile should be balls to the wall.