Did you do the big swim week last week?
Yes? Then let us proceed.
No? Then return to Week-17 and do the big swim week, and just skip this week. Why do I say this? A few reasons. I don't want you to freak out, or hyperventilate, or go through any anxiety-induced problems that cause people to have to DNF (did not finish) in the swim. When this happens it is almost never because a person is not a good enough swimmer, but because the person lacks confidence in his or her swim, and because of a new and strange environment (it being your first triathlon). This week is important for building your confidence.
Also, a big swim week will really turn you into a swimmer, instead of just a person who (oh, by the way) happens to swim. As you slog through the water you won't feel like you're making progress, but trust me, you'll be a lot faster in the water after a big swim week.
Finally, if you get out of the water all tired and wiped out, you've not set yourself up well for the rest of the race. During this week we'll go a long way toward ensuring that you exit the water relatively fresh.
So, it's imperative that you get your big swim week in, unless you come from a heavy swim background.
Assuming that you've got your big swim week behind you, let's repair to the road and dry out. You'll ride a lot this week, and that will take a lot of time. Riding takes about twice the time as running in order to get in an equivalent workout. In order to ride twice the time duration as you run you'll have to ride four times the distance (because you ride about twice as fast as you run). This means if you run, say, 20 miles a week as a triathlete, you'd ride 80 miles in that week in order to achieve relative balance in the two activities. But I frequently like to super-compensate in a particular activity, as you have seen.
Since riding takes so long, you're not going to do too much in the other activities. If there are any issues about comfort or bike position, or if your bike has a problem in the way it functions, you'll become acutely aware of it this week. Whatever the problems are, get them fixed this week or next.
You may find that it becomes difficult to do all the riding I've put in front of you without decent cycling clothes, shoes, and (clipless) pedals. I'm not going to explain what clipless pedals are. If you're not familiar with them, go from here to a search engine and look that term up. The models you'll want to look at are Shimano, Speedplay, and Look. There are others, but these are the industry leaders. As for the shoes, three good choices are Sidi, Shimano, and Carnac, and there are others.
Cycling shorts are the single most important piece of cycling apparel. In 20+ years of cycling I've acquired a closet-full of shorts, jerseys, sleeveless jerseys, bibs, knickers, bib knickers, tights, bib tights, rain gear, shoe covers, arm warmers, vests, ear muffs, blah blah blah. But shorts are half the battle (personally, I prefer cycling bibs over cycling shorts). All the other clothing put together makes up the other half of what's important in cycling comfort.
Lots of ways you can do a big bike week. I'll sometimes turn it into an adventure, like, over a 3-day weekend. You might consider taking a vacation day over a friday or monday and riding your brains out. I've been known to do the "credit card tour," in which I ship shorts and a jersey and a roll of packing tape to a couple of different motels along my route. When I arrive a change of cycling clothing awaits me, and I replace the old clothes in the box, and wrap it back up with the tape. There are several ways you can pre-print the postage labels (shipping your clothes from the motel back to yourself) and throw the labels into the box as well. You're all set.
Or, you can get in your car and drive to a motel in a remote, scenic location, and do 2 or 3 days of riding to and from the motel. Or, you can just ride to and from home. Whatever floats your boat.
SWIMMING: 2 SESSIONS X 1500 - 2500 YARDS PER SESSION
CYCLING: 4 SESSIONS, SLOW, YOUR CHOICE OF DISTANCE
RUNNING: 2 SESSIONS 15-40 MINUTES PER