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2016; 62(9):811-815
a complex and multidimensional health-related behavior.
The literature has described a variety of measurement
methods and techniques, which are classified as direct
and indirect. Examples of direct techniques include the
use of double labeled water, calorimetry, and portable
monitoring through the use of heart rate monitors, pe-
dometers and
accelerometers. As for indirect methods,
we can highlight questionnaires, and self-reports involv-
ing the use of instruments in the form of self-administered
questionnaires, interviews and activity diaries.
8-10
(
D
) The
combination of the calorimetry and doubly labeled water
measurements provides a method for accurate measure-
ment of energy expenditure due to physical activity. How-
ever, they require specific knowledge for application and
interpretation of the results, in addition to being expen-
sive and inconvenient when used in large populations.
Direct calorimetry is based on measuring the amount of
total heat produced by the body in a given period of time.
In turn, indirect calorimetry is based on the total amount
of energy produced from the oxygen consumed in the use
of energy substrates and the production of carbon diox-
ide eliminated by breathing.
11
(
D
)
The method of double labeled water is considered the
gold standard for determining energy expenditure. It is
based on the ingestion of water labeled with radioactive
isotopes of oxygen and hydrogen (the oxygen isotope is
eliminated from the body incorporated into carbon di-
oxide molecules and water; the hydrogen isotope is elim-
inated only as water). As such, the difference between
these two isotopes can predict the measurement of carbon
dioxide production and thereby the energy expenditure,
indirectly.
12
(
C
) This technique is accurate in assessing
the energy expenditure. However, it does not enable an
analysis of the type of physical activity, which is the main
limitation of this method.
Traditionally, subjective methods such as self-admin-
istered questionnaires, notes in diaries and interviews (sur-
veys) are the techniques used
the most for estimating the
total amount of daily or weekly physical activity, remaining
as low-cost tools, and the option used the most in epide-
miological studies.
7
(
B
) Nevertheless, there are limitations
inherent in these instruments, given that they ate dependent
on individual observation and subjective interpretation
and therefore prone to inconsistent evaluations. The use
of motion sensors such as accelerometers and pedometers
has been consolidated as the most frequently used objective
methods for measuring physical activity.
8
(
D
)
A study analyzing the Physical Activity Scale for the
Elderly (PASE) questionnaire aimed at quantifying the
level of physical activity in patients undergoing total knee
arthroplasty demonstrated deficiencies in the validity and
reproducibility of the results when compared to the ac-
celerometer.
13
(
B
) However, in view of the low cost and
simplicity, in epidemiological research, especially large-
scale observational studies, questionnaires are generally
used in the assessment of physical activity, with measure-
ment of varying complexity from the self-administered
form to interviews.
Questionnaires generally provide descriptions of the
patterns of physical activity and can estimate how much
energy individuals spend on a given activity. However,
despite their large scale applicability, the reliability and
validity of the measurement are low.
14,15
(
B
) A systematic
review conducted in order to evaluate questionnaires
aimed at the young population (under 18 years of age)
found that none of the 61 questionnaires identified were
reliable and valid. The same findings were identified when
the focus of the analysis was the adult population.
16,17
(
A
)
To compare the subjective methods (via questionnaires)
with the objective methods (using accelerometers), for
the assessment of physical activity in the population of
children and adolescents (from 3.7 to 19 years), it has
been shown that subjective methods overestimated phys-
ical activity by more than 70% to the detriment of the
objective methods.
18
(
A
)
Another method for the objective assessment of phys-
ical activity is heart rate monitoring based on the linear
relationship between heart rate and energy expenditure.
Relatively inexpensive and with the capacity for minute
by minute heart rate storage, continuous recording by
means of monitors is a method considered feasible and
attractive for the assessment of physical activity. How-
ever, factors such as age, proportion of muscle mass, emo-
tional and cardiorespiratory stress, state of hydration and
fatigue can influence the heart rate/oxygen consumption
ratio. Another limitation is due to the fact that monitor-
ing can mask the patterns of activity given that even after
the cessation of motion the heart rate tends to remain
high, and that in sedentary individuals the heart rate
measured over 24 hours barely surpasses the rest limits,
making it difficult to distinguish between light and mod-
erate activities.
19
(
D
)
On the other hand, mechanical and electronic motion
detectors such as pedometers and accelerometers eliminate
many problems of subjectivity by providing an objective
measurement of physical activity. However, as with all
assessment methods, they possess measurement limita-
tions, such as the ability to discriminate the different
activity types and the seasonal bias inherent at the moment
when the mechanical device is applied.
20
(
C
)