A

aerobic fitness The efficiency with which the
cardiovascular system functions to meet the oxy-
gen needs of cells throughout the body, particu-
larly under the increased pressure of intense
physical activity or exercise. The higher a person’s
aerobic FITNESS LEVEL, the more air the LUNGScan
take in each breath, the more oxygen that enters
the BLOOD, and the more blood the HEARTcan eject
with each contraction. The outcome is that the
cardiovascular system can deliver higher concen-
trations of oxygen to body tissues with less effort,
which increases ENDURANCE. Aerobic fitness is a
key measure of cardiovascular health.

ACTIVITIES THAT IMPROVE AEROBIC FITNESS
aerobic dance basketball bicycling
canoeing cross-country skiing handball
hiking ice skating jogging
kayaking racquetball roller skating
rowing running shooting hoops
snowshoeing soccer spinning
squash stair climbing stationary cycling
step aerobics swimming tennis
treadmill volleyball walking

Physical activities that exercise the muscles to a
level that increases the HEART RATEand BREATHING
rate for a sustained time of 15 minutes or longer
provide an aerobic workout for the body that
strengthens cardiovascular efficiency and
improves aerobic fitness. Consistency is the key
to aerobic fitness. Health experts recommend aer-
obic activity three to four times a week, ideally in
sessions that are 30 to 45 minutes long. The
higher a person’s aerobic fitness level, the easier it
is to sustain aerobic activity for longer periods of
time.

See also AEROBIC CAPACITY; AEROBIC EXERCISE;

AGING, CARDIOVASCULAR CHANGES THAT OCCUR WITH;

CONDITIONING; EXERCISE AND HEALTH; LIFESTYLE AND

HEALTH; MUSCLE; PHYSICAL ACTIVITY RECOMMENDATIONS;

PHYSICAL EXERCISE AND CARDIOVASCULAR HEALTH;

WALKING FOR FITNESS.

aging, cardiovascular changes that occur with

The most significant age-related changes in cardio-

vascular function occur at birth in both sexes and

with MENOPAUSE in women. Though changes in

METABOLISMoccur with aging that affect all body

systems, researchers now believe cardiovascular

health does not inherently decline simply as a

function of aging. DIABETES, OBESITY, lack of physi-

cal exercise, and cigarette smoking are the leading

causes of acquired CARDIOVASCULAR DISEASE (CVD)

among adults. The effects of these factors are

cumulative; they are more likely to result in dis-

ease the longer they exist and the more of them

are present. Accordingly, the risk for acquired car-

diovascular disease increases with age because as

people get older they tend to develop health con-

ditions that set the stage for cardiovascular deteri-

oration. Most researchers believe these risks are

mutable (changeable) through lifestyle.

Cardiovascular Changes at Birth

The cardiovascular system is among the first body

systems to develop in the EMBRYO, with the rudi-

mentary HEARTbeginning to beat at three weeks

gestational age. The heart fully forms, and a rudi-

mentary circulatory network develops and func-

tions, by eight weeks gestational age. Before birth,

the FETUS draws its oxygen supply from its

mother’s BLOODsupply, in an exchange that takes

place across a membrane in the PLACENTA(fetal

9