Although meeting the recommendations of physical activity is reflected in numerous health benefits (26), it does not seem to be usual behavior in developed societies. Recent data obtained by accelerometry in representative samples of United States and Sweden indicate that only ∼8% of adolescents from 12 to 19 yr reached the recommendation of 60 min·d−1 of physical activity of moderate or greater intensity (21) and that less than 5% of adults meet the recommendation of 30 min·d−1 of physical activity of at least moderate intensity, when bouts of 10 min are considered (6,21).
In Portugal, monitoring of adherence to recommendations for physical activity has been carried out only by questionnaire among persons age 15 yr or older. Data reveal that Portugal was, among 15 member states of the European Union, the country with the lowest prevalence of physical activity in leisure time (40.7%) (10) and the sixth country with the highest prevalence of “high physical activity” (in the International Physical Activity Questionnaire (IPAQ)) (33.1%) when also considering professional, domestic, and transport domains (20). Nevertheless, according to public physical activity recommendations for adults (moderate physical activity in the IPAQ), the results indicate that ∼74% of the adult Portuguese population is sufficiently active (3). These results illustrate the difficulty in determining the prevalence of physical activity and its comparison between countries when using questionnaires.
Questionnaires have been the most common methodology for assessing the physical activity of populations or population groups in several countries because of their low cost and their general acceptance by participants. However, some caution is required in the interpretation of self-reported measures as a result of an overestimation error associated in part not only to a bias related to social desirability but also to the cognitive challenges participants have in quantifying the intensity and duration of the activity (25). This is a crucial aspect for effective implementation of the recommendations of the World Health Organization and corresponding policy actions for the promotion of physical activity (27). In this context, the aim of this study was to report the prevalence of the Portuguese population attaining sufficient physical activity in a representative sample of people age 10 yr or older, living in mainland Portugal, objectively assessed using accelerometers.
This study involved a representative sample of the noninstitutionalized population of Portugal, selected by proportionate stratified random sampling taking into account the number of people by age and gender in each region of mainland Portugal (Alentejo, Algarve, Centro, Lisboa, and Norte). The Madeira and Açores regions (Portuguese archipelagos) were not included in this study. A total of 6280 participants were evaluated between 2006 and 2008, but the results are based on 4696 participants with valid records of physical activity. Participants were recruited from schools, work sites, and community settings. The sample was divided into youths (2714 participants, 55% girls), adults (1303 participants, 64% women), and old adults (679 participants, 61% women). The youths were from the school-aged population age 10–17 yr. The adult population consisted of individuals age 18–64 yr. The old adults comprised the population older than 64 yr with an independent physical functioning. The characteristics of the subjects are listed in Table 1. All participants (or their guardians) were informed about the objectives of the study and gave their informed consent to participate in the study. The study was approved by the Portuguese Institute of Sport ethics committee and conducted in accordance with the World Medical Association’s Declaration of Helsinki on human studies (28).
Physical activity was assessed by accelerometry (ActiGraph GT1M model; Fort Walton Beach, FL). The accelerometer used is a small device (3.8 × 3.7 × 1.8 cm, 27 g) that measures the acceleration of normal human movements ignoring high-frequency vibrations associated with mechanical equipment. It contains microprocessor digital filtering that filters accumulated signals within a frequency range of 0.25 to 2.5 Hz, a range designed to detect human movement, and converts them to a numeric value known as a count or movement unit. The ActiGraph GT1M is technologically more advanced than the ActiGraph 7164, the oldest generation of validated ActiGraph monitors (13), particularly concerning calibration, signal detection, memory, initialization, and data downloading. The results of both models in adolescents and adults are, however, comparable, particularly the average counts and time spent in moderate and vigorous physical activity in a range of speeds similar to free-living situations (5,9).
All participants were asked to use an accelerometer on the right hip, near the iliac crest during four consecutive days, including two weekdays and two weekend days (22). The delivery to and reception by the participants of the accelerometers, as well as the explanation of its use, were made personally (24). The devices were activated on the first day at 6.00 a.m., and data were recorded in 15-s epochs because 1-min epochs may result in underestimation of participation in physical activity of moderate or greater intensity, particularly in youths (22). The device activation and data download were performed using the software ActiLife Lifestyle (v.3.2; Fort Walton Beach, FL). Processing was done with the program MAHUffe v.22.214.171.124 (available from www.mrc-epid.cam.ac.uk) from the original downloaded files (in DAT format). For the analyses, a valid day was defined as having 600 min (10 h) or more of monitor wear, corresponding to the minimum daily use of the accelerometer (24).
Apart from accelerometer nonwear time (i.e., when it was removed for sleeping or water activities), periods of at least 60 consecutive minutes of zero activity intensity counts were also considered nonwear time. The study included the results from participants with at least three valid days (including one weekend day), with at least 10 h of wear time per day, meaning that 4696 participants were considered and 1584 participants were excluded for not complying with these conditions, specifically, 818 youths (47% girls), 417 adults (57% women), and 349 old adults (63% women). Excluded participants up to 17 yr and older than 64 yr were older than their peers of the same age group, whereas participants 18–64 yr were younger than their respective counterparts. In general, there were no differences in body mass index between participants with at least three valid days and those who did not meet this criterion.
The amount of activity assessed by accelerometry was expressed as the minutes per day spent in different intensities and in 10-min bouts of physical activity of moderate or greater intensity, the mean time (min·d−1) of total physical activity (light, moderate, and vigorous), and the mean intensity of physical activity (counts per minute per day).
The cutoff values used to define the intensity of physical activity and therefore to quantify the mean time in each intensity (sedentary, light, moderate, or vigorous) for persons age 18 yr or older were the following: sedentary = <100 counts per minute, light = 100–2019 counts per minute, moderate = 2020–5998 counts per minute (corresponding to 3–5.9 METs), and vigorous = ≥5999 counts per minute (corresponding to ≥6 METs) (21).
For youths age 10–17 yr, 4 METs was used as a criterion for moderate intensity, and 7 METs was used for vigorous intensity, to adjust for the higher level of resting energy expenditure in younger people. To this end, we determined the age-specific cutoff values according to the equation proposed by Trost et al. (23).
For comparison with physical activity recommendations for public health, modified 10-min bouts of physical activity of moderate or greater intensity were defined as 10 or more consecutive minutes above the respective cutoff value, with allowance for 1 min in every 5 min below the threshold (14). Although no cut point has been established for bouts of physical activity in youths, modified 10-min bouts were also calculated in participants up to 17 yr for the purpose of comparison with adults and old adults.
To analyze adherence to physical activity recommendations for public health, we considered the accumulation of at least 30 min of activity of moderate or greater intensity (adults and older adults) or 60 min (youths) of physical activity of moderate or greater intensity per day.
All analyses were conducted with the statistics software PASW Statistics for Windows v.18.0, 2009 (SPSS, Inc., Chicago, IL). For all tests, statistical significance was set at P ≤ 0.05. Descriptive characteristics and physical activity data of the participants are presented as mean ± SD and mean ± SE, respectively. Comparison of physical activity between age groups and genders was performed using ANCOVA with Bonferroni adjustment for average monitor-wearing time because this variable was associated positively with sedentary and light physical activity (12). We tested the levels responsible for differences between age groups by performing multiple comparisons with Bonferroni adjustment. Comparison of physical characteristics of the sample between genders was performed using an independent-sample t-test, whereas comparisons between age groups were tested using one-way ANOVA with post hoc analysis, using the Scheffé test if there was homogeneity of variances (P ≥ 0.05) or the Dunnett T3 test in cases of heterogeneous variances (P ≤ 0.05). All variables were checked for normality. We excluded records of average-intensity physical activity above 1500 counts per minute (one old participant) from the statistical analysis because they constitute spurious data (11).
Physical activity is presented in Table 2, including sedentary, light, moderate, vigorous, and total activity.
Sedentary and light activity
In general, boys up to 17 yr revealed less sedentary and more light activity than other male age groups, whereas the greatest sedentary and the lowest light activity was seen in males older than 64 yr. Females older than 64 yr also showed the greatest sedentary and the lowest light activity compared with other female age groups. However, the lowest sedentary time was observed in females between 18 and 64 yr. Males demonstrated less sedentary and more light activity than females, especially up to the age of 17 yr.
Moderate and vigorous physical activity
Boys up to 17 yr had more vigorous physical activity than other male age groups but just higher moderate physical activity than males older than 64 yr. The oldest male group demonstrated lower moderate and vigorous physical activity than males age 18–64 yr. In females, 18- to 64-yr-old women revealed higher values of moderate physical activity than girls age 10–17 yr, who, in turn, presented higher values than women older than 64 yr. As with boys, girls up to 17 yr also showed more vigorous physical activity than other female age groups, with the lowest values presented by females older than 64 yr. Considering gender, males spent more time in moderate physical activity than females up to the age of 29 and after 64 yr but more time in vigorous physical activity in all age groups.
Figure 1 shows the mean values of physical activity of moderate or greater intensity counting every minute (A) and modified 10-min bouts (B). When one examines the cumulative daily physical activity accounting only for periods equal to or greater than 10 min of moderate or greater intensity and not the sum of all minutes spent at this intensity, the mean values of the 18- to 64-yr age group were superior to those of the other age groups in both genders but lower than what is recommended for people older than 17 yr.
Total physical activity and average intensity
Total physical activity (light, moderate, and vigorous) revealed that the highest values were observed in boys up to 17 yr and females between 18 and 64 yr. The age group of 65 yr or older showed the lowest values (Table 2). Figure 2 presents in summary form the results for the average intensity of activity, expressed in counts per minute per day, for all ages. In men, there was a decrease in physical activity between the ages of 10 and ∼30 yr, followed by maintenance until around the age of 50 yr with further reductions after that age. In women, there was a decrease in physical activity between the ages of 10 and ∼20 yr with an increase up to the age of 50 yr, when, as in men, there was a further decrease, although even greater. This leads to an increase in physical activity differences between the genders with age.
Prevalence of sufficient physical activity
The estimation of the percentage of persons sufficiently active according to the recommendations for physical activity of moderate or greater intensity is presented in Table 3. This estimation was based on counting all the minutes at this intensity and periods equal to or greater than 10 min.
In accordance with the recommendation of 60 min·d−1 of physical activity of moderate or greater intensity, 36% of youths age 10–11 yr (51.6% of boys and 22.5% of girls) and only 4% of youths age 16–17 yr (7.9% of boys and 1.2% of girls) were considered sufficiently active, with a progressive decrease in prevalence between those ages. In adulthood, ∼70% of people age 18–64 yr (76.6% men and 65.2% women) and 35% of people older than 64 yr (46% of men and 29% of women) reached the recommended 30 min·d−1 of physical activity, when every minute of moderate or greater intensity is counted. When considered as periods of 10 min or more of moderate or greater intensity, the prevalence was 4%–6% at 18–39 yr, 7%–9% at 40–64 yr, and ∼3% at 65 yr and older.
For a better understanding of the needs for surveillance and intervention for promoting physical activity, the National Physical Activity Register conducted its assessment on a representative sample of the Portuguese population with a methodology similar to that used in 2003–2004 in the United States under the National Health and Nutritional Examination Survey, which objectively assesses physical activity on a population basis (21). This is, however, the first report documenting the prevalence of physical activity in a representative sample of the Portuguese population, aged 10 yr and older using accelerometry.
Variation in physical activity with age and gender
The results show some of the trends previously found with self-report and accelerometer data, namely, a decrease in physical activity with age in youths up to 17 yr and old people older than 64 yr and higher physical activity in males compared with females in almost all age groups (1–4,7,15,20,21). As observed in some countries (females from New Zealand, China, Hong Kong, and Saudi Arabia) (3), the results do not confirm that physical activity is lower in successive age groups (21) because the average physical activity intensity increases at around the ages of 20 yr in women and 30 yr in men, remaining relatively stable after until the age of 50 yr. After 50 yr, there is again a decrease in average intensity and moderate plus vigorous physical activity, reaching its lowest values after 65 yr.
In Portugal, adult women are, on average, more active than girls, which seems to occur also in the United States in Hispanic women (6,8) but not in non-Hispanic women (21). A possible difference in physical activity between the Portuguese and US populations seems to occur among adult women, with Portuguese women demonstrating higher values of physical activity of average intensity and moderate or greater intensity than American women in general (21). This hypothetical fact cannot be explained by dissimilarity between ActiGraphs (GT1M vs 7164) and epochs (15 s vs 1 min) used in Portugal and United States, respectively, because the higher threshold for nonzero counts in the GT1M compared with the 7164 ActiGraph may lead to underestimation of time spent in light-intensity activity (and consequently, in average-intensity activity) (9). On the other hand, the 1-min epochs may result in underestimation of physical activity of moderate or greater intensity, particularly when activity is characterized by frequent bursts of short duration, which is not the case of physical activity in the adult population (24). Comparative results of physical activity among the adult population of Sweden and the United States also show that Swedish females were more active (more counts per minute and physical activity of moderate or higher intensity) than US females, with no relevant differences between males of these two countries (7).
Among Portuguese adult women, physical activity is higher for the 40- to 50-yr period, during which average-intensity physical activity for women is higher than that for men. This seems to be in accordance with self-reported physical activity previously observed not only in Portugal but also in Argentina and Saudi Arabia, which contradicted the general trend of higher prevalence of physical activity in adult men (3). Current data show that in Portugal, this trend is reversed between 40 and 50 yr and due to higher values of light (and not moderate plus vigorous) physical activity in women compared with men of these ages.
With the exception of ages 40–50, males are more active than females with more marked differences among young people. In youths, this difference is attenuated with age because of a decrease in the average intensity that is more pronounced in boys than in girls. This decrease in physical activity continues until the third decade in males, representing a decrease of about 25% compared with values recorded for ages 10–11, whereas in girls, this decrease occurs until around the end of the second decade, representing a decrease of ∼18%.
Accelerometer data in young people age 3–18 yr have been collected in different countries. However, differences in age grouping and variety of methods used to analyze raw accelerometry files limit the comparison of physical activity variables such as minutes spent in moderate or greater intensity (19). Considering the average-intensity activity, a decrease in physical activity during adolescence years and lower levels in girls compared with boys, namely, from ∼500 to 600 counts per minute at 10–15 yr to ∼400 counts per minute at 16–19 yr in boys and from ∼400 to 500 counts per minute at 10–15 yr to ∼300 counts per minute at 16–19 yr in girls, were observed in this and other studies (1,17,21).
Prevalence of sufficient physical activity
According to the guidelines for physical activity (16,26), the results showed a prevalence of sufficient physical activity in 70% of adults of 18–64 yr. The prevalence of physical activity was lower in people age 65 yr or older (35%) and youths age 10–17 yr (36% and 4%, respectively). This lower prevalence among young people is due to more demanding physical activity recommendations (60 min for children and young people and 30 min for other ages) as well as more demanding cutoff values for moderate intensity (from 2059 counts per minute at age 11 to 3239 at age 17 vs 2020 counts per min at age 18 or older) because youths, especially boys, represent the most active population group. Consequently, between the ages of 10 and 17 yr, there was a decrease of ∼55% of physical activity of moderate or greater intensity (minutes per day, depending on the cutoff values) and only a ∼20% decrease in average physical activity intensity (counts per minute, not dependent on the cutoff values), in both boys and girls.
The prevalence of physical activity evaluated by accelerometry in the adult Portuguese population was similar tothat observed in Portugal in 2002 by the International Prevalence Study on Physical Activity (70% vs 74% of adults) (3) and almost twice that evaluated by the Special Eurobarometer Wave 58.2 (70% vs 33% of adults) (20), both studies with IPAQ. However, whereas the Special Eurobarometer Wave 58.2 defined 3000 MET·min·wk−1 during 7 d or 1500 MET·min·wk−1 of vigorous-intensity activity accumulated during 3 d or more, i.e., the IPAQ “high active” category, as a criterion for sufficient total activity, the International Physical Activity Prevalence Study defined the IPAQ “moderate active” category, which indicates meeting physical activity guidelines of 30 min of moderate-intensity activity 5 d·wk−1, 20 min of vigorous activity 3 d·wk−1, or a combination achieving at least 600 MET·min·wk−1 for >10 min at a time, as a criterion. However, when blocks of 10 min of continuous activity of moderate or greater intensity were considered, the prevalence of the active population decreased dramatically, varying from 3% at ages older than 64 to 9% between ages 40 and 64. A large reduction in the prevalence of physical activity, from 52% to 1%, was also observed in Sweden in the adult population age 18–69 yr, when considering the accumulation of at least 30 min of physical activity of moderate or greater intensity and 10-min bouts, respectively (7). A very low prevalence of physical activity was also observed in the United States when considering 10-min bouts. However, the Portuguese population showed higher values of prevalence especially in women age 20–59 yr (Portuguese = 7.5% vs American = 3.2%) (21).
The huge gap between the prevalence when considering only every minute or periods of 8–10 min shows that physical activity of moderate or greater intensity is maintained for periods that are too short and/or frequently interrupted. Most structured (leisure and sports) and unstructured (occupational and domestic) physical activities have these characteristics. Apart from walking, jogging, and running performed with exercise intention, most ambulatory activities are intermittent in nature. The fact that people age 40–64 yr had a greater prevalence of physical activity when considering bouts of 10 min shows a greater preponderance of more continuous activities in leisure time as opposed to intermittent activities, probably dominant in younger ages. For example, 60 min of tennis is accounted for entirely by the IPAQ but only in part or only in a small part by the accelerometer, considering the accumulation of every minute or 10-min bouts of physical activity at moderate or greater intensity, respectively. In this context, consideration of cumulative physical effort for periods of 10 min or more when physical activity is assessed objectively seems to be inadequate in relation to current recommendations for people older than 17 yr that are based on the epidemiological association between self-reported physical activity and health.
The strengths of our study include a large sample of youth, adult, and old adult participants and the objective evaluation of physical activity, namely, the use of the ActiGraph GT1M that seems to be a more consistent measurement tool than previous ActiGraphs. The GT1M accelerometer might reduce measurement variability in studies in which a large number of physical activity monitor units are used (18). According to Rothney et al. (18), if data from GT1M monitors are partitioned into intensity categories with equations developed for the 7164, only a small number of count values close to the intensities’ cut points are reclassified. Differences between the GT1M and 7164 monitors may be significant especially if energy expenditure is the desired outcome, which was not the case in the present work. The main limitations of the study are related to the need for a greater number of days of monitoring (7 d), particularly in youths, to reliably estimate habitual physical activity. However, overall study costs determined the 3-d period of monitoring. To compare results of physical activity prevalence between Portugal and the United States, cut points chosen for vigorous and moderate activity were the same as those used by Troiano et al. (21) with the limitations already described by the authors.
Light physical activity accounted for a large proportion of average-intensity physical activity in women, and thus, counts per minutes may be a better indicator of physical activity. The observed prevalence differences between every minute and sustained bouts of activity raise the question about the need for bouts of physical activity when physical activity is measured objectively. Young and old people, particularly girls and women, showed the lowest values in practice and should thus be target groups for prevention strategies aimed at increasing physical activity.
This work was supported by the Portuguese Institute of Sport.
The authors thank all technical staff involved in data collection procedures.
The authors have no conflict of interest.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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