Let's say you start a weight-training program. You go to the gym, buy a membership, and start pumping iron. What happens? You get up the next morning and your arms say, "No way, Jose! We're taking the day off. In fact, we're taking the rest of the week off!"

Or, you lift something you ought not to have lifted and, poof, your back goes out and you're toast.

Not so your heart. It goes and goes. Day and night, twenty-four seven. It never complains.

In a way, that's just the problem. Your heart never gives you any notice that it's tired. Therefore, you take it for granted, and you push and push. When it finally does get tired, you'll probably not know that it's tired. You'll probably just feel sluggish, and think you need a rest. Which you do. But you might not realize that the rest of your body is fine, it's your heart that's tired.

There isn't unanimous consent among the scientific community that the heart can get tired. But there are so many otherwise fit triathletes I know who, after decades of competition, have pacemakers, who suffer from atrial fibrillation and, unfortunately, who've suffered heart attacks while training, that I don't feel I need to wait until such unanimity exists before I write that you ought to consider the work your heart performs in the course of your triathlon career.

Becoming "heart-tired" certainly never happens to baseball players. But I think it occasionally happens to triathletes. Why? Because we give that heart so many opportunities to work, we don't realize how much work we're asking it to do. Let's take your triathlon workouts as an example. Let's say you're on a master's swim team, and you're swimming four times a week. If you're hard at it, you might be going at a rate during the workout that is around 90% of your max heart rate. That's what we call a "high-quality" effort. "Quality" versus "quantity" I'm talking about.

Now, if you're running 3 times a week, and you're cycling 3 times a week, add that to your swim sessions and that's 10 workouts a week. If you're going hard all the time—if all your workouts are "quality"—your heart is pumping like crazy 10 times per week. Pretty soon that sucker'll get tired.

As I said, that doesn't happen to other athletes, even runners, because they don't often perform a high heart rate workout 10 times per week, and if they do—and if they go hard every run—their bodies will probably break down somewhere else before their hearts give out. But triathletes can train long and hard and often, because they're switching sports, which means switching muscles. You tire your arms out swimming, no problem! Time to ride the bike!

Be careful. Whether you're a top pro or a rank beginner, you've got to think about your heart. A good rule of thumb is to keep your quality workouts—those in which your heart rate is getting above 85% of your maximum for long periods of time—to no more than 5 per week.

MISSION
Your goal is simply to start thinking about your rate of effort. You can buy a heart rate monitor, or you can simply stop every now and then and take your pulse. What is your maximum heart rate? There is a pretty good approximation, and that is 220 minus your age. Another way is to actually buy a heart rate monitor and wear it. At some point during your workouts—perhaps climbing a big hill during a run—you'll get to a point where you're really working very hard and your pulse just isn't climbing any more. That's your max, or close to it.

Your mission this week is one of omission. It is not what you're supposed to do that I'm interested in, it's what you're not supposed to do, which is have more than 5 quality sessions per week. You can have less. You can have none, as far as I'm concerned. Just no more than 5. One interesting thing about the heart. There is a way to know if you've tired your heart out. It's hard to tell this unless you keep a regular and close watch on your pulse. People who are "heart tired" find that they can't get their pulse up. In other words, they'll normally do a particularly workout––and at a particular effort level––with a pulse of, say, 155 beats per minute. But on a particular day the pulse won't go past, say, 125. That's a clue that your heart is tired. When that happens you spend a week or two doing workouts that keep your pulse below 110 or 120 beats per minute.

Fortunately, you're probably not doing enough volume for that to be a problem. Yet.

EXECUTION
The tough thing is to keep your pulse down during the swim. Especially if you belong to a master's swim team. You may have to move down to a slower lane. Or move entirely over to "lap swim" a day per week. Use your best judgment. Just be reasonable. My goal here is just to get you thinking about that big muscle that you probably don't think about very much. It'd be a pretty bad scene if it decided to bail on you.

SWIMMING: 3 OR 4 SESSIONS X 1000 - 3000 YARDS PER SESSION
1 SESSION SHOULD BE A LONG, STRAIGHT SWIM.
CYCLING: 1 OR 2 SESSIONS OF 60 MINUTES EACH; 1 RIDE OF 30-40 MILES
RUNNING: 2 OR 3 SESSIONS X 25-35 MINUTES PER SESSION; 1 X 75-80 MINUTES