This section provides definitions for many terms important to physical
activity and health. It has been adapted from the glossary provided in the
Physical Activity Guidelines Advisory
Committee Report. It is not
meant to be an exhaustive list, and definitions of additional terms can be
found in the Committee's report.
Absolute intensity. See Intensity.
Accumulate.The concept of meeting a specific physical
activity dose or goal by performing activity in short bouts, then adding
together the time spent during each of these bouts. For example, a goal of 30
minutes a day could be met by performing 3 bouts of 10 minutes each throughout
Adaptation.The body's response to exercise or
activity. Some of the body's structures and functions favorably adjust to
the increase in demands placed on them whenever physical activity of a greater
amount or higher intensity is performed than what is usual for the individual.
These adaptations are the basis for much of the improved health and fitness
associated with increases in physical activity.
Adverse event. In the context of physical activity, a
negative health event. Examples of adverse events as a result of physical
activity include musculoskeletal injuries (injury to bone, muscles, or joints),
heat-related conditions (heat exhaustion), and cardiovascular (heart attack or
Aerobic capacity. See Maximal oxygen
Aerobic physical activity. Activity in which the
body's large muscles move in a rhythmic manner for a sustained period of
time. Aerobic activity, also called endurance activity, improves
cardiorespiratory fitness. Examples include walking, running, and swimming, and
Balance. A performance-related component of physical
fitness that involves the maintenance of the body's equilibrium while
stationary or moving.
Balance training. Static and dynamic exercises that
are designed to improve individuals' ability to withstand challenges from
postural sway or destabilizing stimuli caused by self-motion, the environment,
or other objects.
Baseline activity. The light-intensity activities of
daily life, such as standing, walking slowly, and lifting lightweight objects.
People who do only baseline activity are considered to be inactive.
Body composition. A health-related component of
physical fitness that applies to body weight and the relative amounts of
muscle, fat, bone, and other vital tissues of the body. Most often, the
components are limited to fat and lean body mass (or fat-free mass).
Bone-strengthening activity. Physical activity
primarily designed to increase the strength of specific sites in bones that
make up the skeletal system. bone strengthening activities produce an impact or
tension force on the bones that promotes bone growth and strength. Running,
jumping rope, and lifting weights are examples of bone-strengthening
Cardiorespiratory fitness (endurance). A
health-related component of physical fitness that is the ability of the
circulatory and respiratory systems to supply oxygen during sustained physical
activity. Cardiorespiratory fitness is usually expressed as measured or
estimated maximal oxygen uptake (VO2max). See Maximal oxygen
Dose response. The relation between the dose of
physical activity and the health or fitness outcome of interest. In the field
of physical activity, "dose" refers to the amount of physical
activity performed by the subject or participants. The total dose, or amount,
is determined by the three components of activity: frequency, duration, and
Duration. The length of time in which an activity or
exercise is performed. Duration is generally expressed in minutes.
Endurance activity. See Aerobic physical
Exercise. A subcategory of physical activity that is
planned, structured, repetitive, and purposive in the sense that the
improvement or maintenance of one or more components of physical fitness is the
objective. "Exercise" and "exercise training" frequently
are used interchangeably and generally refer to physical activity performed
during leisure time with the primary purpose of improving or maintaining
physical fitness, physical performance, or health.
Fitness. See Physical fitness.
Flexibility. A health- and performance-related
component of physical fitness that is the range of motion possible at a joint.
Flexibility is specific to each joint and depends on a number of specific
variables, including but not limited to the tightness of specific ligaments and
tendons. Flexibility exercises enhance the ability of a joint to move through
its full range of motion.
Frequency. The number of times an exercise or activity
is performed. Frequency is generally expressed in sessions, episodes, or bouts
Health. A human condition with physical, social and
psychological dimensions, each characterized on a continuum with positive and
negative poles. Positive health is associated with a capacity to enjoy life and
to withstand challenges; it is not merely the absence of disease. Negative
health is associated with illness, and in the extreme, with premature death.
Health-enhancing physical activity. Activity that,
when added to baseline activity, produces health benefits. Brisk walking,
jumping rope, dancing, playing tennis or soccer, lifting weights, climbing on
playground equipment at recess, and doing yoga are all examples of
health-enhancing physical activity.
Health-related fitness. A type of physical fitness
that includes cardiorespiratory fitness, muscular strength and endurance, body
composition, flexibility, and balance.
Intensity. Intensity refers to how much work is being
performed or the magnitude of the effort required to perform an activity or
exercise. Intensity can be expressed either in absolute or
- Absolute. The absolute intensity of an activity is
determined by the rate of work being performed and does not take into account
the physiologic capacity of the individual. For aerobic activity, absolute
intensity typically is expressed as the rate of energy expenditure (for
example, milliliters per kilogram per minute of oxygen being consumed,
kilocalories per minute, or METs) or, for some activities, simply as the speed
of the activity (for example, walking at 3 miles an hour, jogging at 6 miles an
hour), or physiologic response to the intensity (for example, heart rate). For
resistance activity or exercise, intensity frequently is expressed as the
amount of weight lifted or moved.
- Relative. Relative intensity takes into account or
adjusts for a person's exercise capacity. For aerobic exercise, relative
intensity is expressed as a percent of a person's aerobic capacity
(VO2max) or VO2 reserve, or as a percent of a person's measured or
estimated maximum heart rate (heart rate reserve). It also can be expressed as
an index of how hard the person feels he or she is exercising (for example, a 0
to 10 scale).
Lifestyle activities. This term is frequently used to
encompass activities that a person carries out in the course of daily life and
that can contribute to sizeable energy expenditure. Examples include taking the
stairs instead of using the elevator, walking to do errands instead of driving,
getting off a bus one stop early, or parking farther away than usual to walk to
Maximal oxygen uptake (VO2max). The body's
capacity to transport and use oxygen during a maximal exertion involving
dynamic contraction of large muscle groups, such as during running or cycling.
Also known as maximal aerobic power and cardiorespiratory endurance capacity.
MET. MET refers to metabolic equivalent, and 1 MET is
the rate of energy expenditure while sitting at rest. It is taken by convention
to be an oxygen uptake of 3.5 milliliters per kilogram of body weight per
minute. Physical activities frequently are classified by their intensity using
the MET as a reference.
Moderate-intensity physical activity. On an absolute
scale, physical activity that is done at 3.0 to 5.9 times the intensity of
rest. On a scale relative to an individual's personal capacity,
moderate-intensity physical activity is usually a 5 or 6 on a scale of 0 to 10.
Muscle-strengthening activity (strength training, resistance
training, or muscular strength and endurance exercises). Physical
activity, including exercise, that increases skeletal muscle strength, power,
endurance, and mass.
Overload. The amount of new activity added to a
person's usual level of activity. The risk of injury to bones, muscles,
and joints is directly related to the size of the gap between these two levels.
This gap is called the amount of overload.
Performance-related fitness. Those attributes that
significantly contribute to athletic performance, including aerobic endurance
or power, muscle strength and power, speed of movement, and reaction time.
Physical activity. Any bodily movement produced by the
contraction of skeletal muscle that increases energy expenditure above a basal
level. In these Guidelines, physical activity generally refers to the subset of
physical activity that enhances health.
Physical fitness. The ability to carry out daily tasks
with vigor and alertness, without undue fatigue, and with ample energy to enjoy
leisure-time pursuits and respond to emergencies. Physical fitness includes a
number of components consisting of cardiorespiratory endurance (aerobic power),
skeletal muscle endurance, skeletal muscle strength, skeletal muscle power,
flexibility, balance, speed of movement, reaction time, and body composition.
Progression. The process of increasing the intensity,
duration, frequency, or amount of activity or exercise as the body adapts to a
given activity pattern.
Relative intensity. See Intensity.
Relative risk. The risk of a (typically) adverse
health outcome among a group of people with a certain condition compared to a
group of people without the condition. In physical activity, relative risk is
typically the ratio of the risk of a disease or disorder when comparing groups
of people who vary in their amount of physical activity.
Repetitions. The number of times a person lifts a
weight in muscle-strengthening activities. Repetitions are analogous to
duration in aerobic activity.
Resistance training. See Muscle-strengthening
Specificity. A principle of exercise physiology that
indicates that physiologic changes in the human body in response to physical
activity are highly dependent on the type of physical activity. For example,
the physiologic effects of walking are largely specific to the lower body and
the cardiovascular system.
Strength. A health and performance component of
physical fitness that is the ability of a muscle or muscle group to exert
Strength training. See Muscle-strengthening
Vigorous-intensity physical activity. On an absolute
scale, physical activity that is done at 6.0 or more times the intensity of
rest. On a scale relative to an individual's personal capacity,
vigorous-intensity physical activity is usually a 7 or 8 on a scale of 0 to 10.
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