you’re in, the faster your heart rate drops. Ideally, your heart rate should
plunge at least 20 beats in the first minute. People in really good shape drop
40 beats or more. Keep track of this measure. You’ll see a gradual improve-
ment over a period of weeks and months. (Taking prescription or over-the-
counter medication may affect the way your heart and blood pressure
respond to exercise. Check with your doctor about this.)
As we mention in Chapter 2, monitoring your resting heart rate is also a good
idea. Your resting heart rateis the number of times your heart beats per
minute when you’re just sitting around. When you start exercising, your rest-
ing heart rate may be as high as 90. But after a few months of exercising, your
resting heart rate may drop 10 or 20 beats. Some top athletes in endurance
sports have resting heart rates as low as 30 beats per minute. However, don’t
compare your heart rate to anyone else’s. Your resting heart rate is partly
determined by heredity.
Your resting heart rate also can tell you a lot about your recovery from day to
day. Keep your monitor by your bed and strap it on first thing in the morning,
on a daily basis. Or, take your pulse manually. If your heart rate is ten beats
higher than usual, you probably haven’t recovered from yesterday’s workout.
Your target heart-rate zone
Your heart rate can tell you so much about your body — how fit you are, how
much you’ve improved, and whether you’ve recovered from yesterday’s
workout. But how do you know what heart rate to aim for? There’s no magic
number. Rather, there’s a whole range of acceptable numbers, commonly
called your target heart-rate zone.This range is the middle ground between
slacking off and knocking yourself out. Typically, your target zone(as it’s
called for short) is between 50 percent and 85 percent of your maximum
heart rate,the maximum number of times your heart should beat in a minute
without dangerously overexerting yourself.
The point at which your body switches from using oxygen as its primary
source of energy to using stored sugar is referred to as your anaerobic thresh-
old.(You may also hear this referred to as the point at which lactic acidbuilds
up.) When you’re in poor physical shape, your body isn’t very efficient at
taking in oxygen, and you hit your anaerobic threshold while exercising
at relatively low levels of exercise. As you become more fit, you’re able to go
farther and faster, yet still supply oxygen to your muscles. If a couch potato
tries to run an eight-minute-mile pace, he’s going to go anaerobic pretty darned
fast. An elite runner can run an entire marathon at about a five-minute-mile
pace and still stay primarily aerobic.
At the low end of your zone, you’re barely breaking a sweat; at the high end,
you’re dripping like a Kentucky Derby winner. If you’re a beginner, stick to the
lower end so you can move along comfortably for longer periods of time and
Chapter 8: Cardio Crash Course 111