Triathlon training
 

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What distance?

If he is 45 and has a pot belly just be careful that you don't over train him. I am sure it is a sprint distance and all he needs is a linear progression beginners weightlifting routine with 1 day of each element of the race. Meaning one day of run, one of bike and one swim. All of these need to be down in the 65 to 80 percent heart rate range. If he is adapting well you can do one brick on the weekend where you run and bike or bike and swim.

If your friend has never done triathlons before he needs to learn about the rules and how to transition. That will make for a more enjoyable race day.

I think you might want to make sure he knows what he's getting himself into. It sounds like he might have a fair amount of work ahead of him to prepare for a triathlon. Is he going to enjoy it enough for it to be worth it?