Chapter 15 Staying Physically Active: A Way of Life
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intensity of exercising increases. The
goal of aerobic exercise is to increase
your heart and breathing rates to safe
levels for an extended time. Most
fi tness experts recommend holding
these raised levels for 20 to 60 minutes
to get the most cardiorespiratory
benefi ts. Walking, jogging, in-line
skating, bicycling, and swimming laps
are examples of aerobic activities, 15-6.
Anaerobic activities are activi-
ties in which your muscles are using
oxygen faster than your heart and
lungs can deliver it. Anaerobic fi tness
means you are able to lift or move
objects forcefully as required for use in
every day activities. Anaerobic activi-
ties use short, intense bursts of energy
that make you feel like you need to
catch your breath. Muscles rely on a
limited supply of glucose and energy
is released quickly. For example, sprint
events and sports such as football,
baseball, tennis, or a 100-meter race
are anaerobic activities. They cannot
be sustained long enough to help you
increase cardiorespiratory fi tness. This
is because you must stop often during
anaerobic activities to catch your
breath. Anaerobic activities can help
you build strength, power, and speed.
Muscular Endurance
Muscular endurance refers to your
ability to use a group of muscles over
and over without becoming tired. For
instance, muscular endurance allows
you to use your leg muscles to continu-
ously pedal a bicycle throughout an
hour-long ride. Muscular endurance
helps you perform physical activi-
ties comfortably. It also enables you to
remain active for extended periods.
Some people have more endurance
in one muscle group than in another.
For instance, people trained as runners
are bound to have developed endur-
ance in their leg muscles. However,
they may fi nd it hard to swim several
laps without their arms tiring. This is
why it is important to work on devel-
oping all your muscle groups. Hiking,
rowing, skating, and gymnastics can
help you develop muscular endurance.
Strength
Strength is the ability of the muscles
to move objects. It is usually measured
in terms of how much weight you can
15-6 Using the muscles of the arms and
legs while breathing rhythmically makes
swimming an excellent aerobic activity.
Calculating Resting Heart Rate
The resting heart rate averages between 60
and 80 beats per minute. Jack, a nonathlete, has a
resting heart rate of 70 beats per minute. His friend,
Joe, runs cross country and has a resting heart rate
of 40 beats per minute. Joe’s stronger heart pumps
more blood with fewer beats.
• How much faster is Jack’s resting heart rate
than Joe’s?
Math Link