Health Education Research, Vol. 16, No. 3, 335-341,
June 2001
© 2001 Oxford University Press
A comparison of adolescent moderate-to-vigorous physical activity participation in relation to a sustained or accumulated criterion
Sport and Health, Liverpool Hope University College, Hope Park, Liverpool L16 9JD,
1 School of Leisure and Sports Studies, Leeds Metropolitan University, Leeds LS6 3QS and
2 School of Sport, Performance and Leisure, University of Wolverhampton, Walsall WS1 3BD, UK
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Abstract |
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Contemporary guidelines for young people advocate both a sustained and accumulative approach to moderate-to-vigorous physical activity (MVPA) participation. In order to investigate the behavioural significance of applying these approaches, this study assessed if differences in adolescent MVPA occurred when either a sustained or accumulated criterion was adopted. Using heart rate thresholds indicative of intensity, the physical activity of 25 adolescents was assessed by monitoring heart rate over 3 days. Results indicated that differences in MVPA parti5 cipation did exist when different approaches were used, in that the majority of adolescents were active with respect to an accumulated criterion yet inactive with respect to a sustained criterion. Such a disparity may be due to accumulative MVPA being more characteristic of young people's natural activity behaviour. Such findings have strong implications for practitioners seeking to counter young people's inactivity, in that the application of an accumulative approach may be more effective at initiating and establishing an habitual activity behaviour than that of a sustained approach.
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Introduction |
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In recognition that habitual physical activity may bring about a range of health-related benefits, the last decade has seen the development of guidelines specifically aimed at young people (Sallis and Patrick, 1994
; Health Education Authority, 1998). Such guidelines advocate two approaches.
The first approach suggests that young people should participate in 20 min or more of continuous moderate-to-vigorous physical activity (MVPA) participation, at least 2 (Health Education Authority, 1998) or 3 (Sallis and Patrick, 1994) times a week. This reflects the tenets of the Exercise Prescription Model (EPM) (American College of Sports Medicine, 1990) which suggests three to five sustained, high-intensity activity periods a week which incorporate the use of large muscle groups in rhythmical action.
The second approach suggests that MVPA should be accumulated throughout each day. While those guidelines drafted by Sallis and Patrick do not specify optimal duration (Sallis and Patrick, 1994), the Health Education Authority suggests that young people should accumulate at least 30 min and ideally 60 min of MVPA a day (Health Education Authority, 1998). This reflects the more recent advance of the Children's Lifetime Physical Activity Model (C-LPAM) (Corbin et al., 1994), which suggests an energy expenditure of 6–8 kcal/kg/day or 42–56 kcal/kg/week. In contrast to the EPM, the C-LPAM recognizes the importance of incorporating activities such as walking, riding a bike or play into everyday life, focusing on levels of MVPA associated directly with health rather than those associated with the attainment of fitness.
While both the EPM and C-LPAM imply that physical activity should be of a moderate-to-vigorous intensity, such approaches clearly differ with respect to the type of physical activity they recommend. While the EPM indicates that MVPA should be sustained and prescriptive, the C-LPAM indicates that MVPA should be accumulated and lifestyle orientated. Such a fundamental difference creates the dilemma of which approach is most appropriately applied to young people. It could be argued that the validity of any application should be judged by its ability to positively influence physiological health. The rationales which accompany those guidelines described support the suggestion that both the EPM and C-LPAM are able to infer such benefits (Sallis and Patrick, 1994; Health Education Authority, 1998). Indeed, it may be suggested that the majority of guideline research and discussion continues to be centred around establishing the optimal volume of physical activity necessary to bring about physiological adaptations (i.e. the dose–response relationship) (Riddoch and Boreham, 1995; Health Education Authority, 1997, 1998). However, it should also be argued that the prescription of physical activity to young people should not entirely reside within a physiological context, but should also rest with the capacity to determine regular participation. Indeed, such a capacity may be deemed essential in light of recent suggestions that habitual childhood MVPA positively influences participation across the life span (Malina, 1996) and may therefore regulate risk factors such as hyperlipidemia or low peak bone mineral density which may evolve into health-threatening disease states such as atherosclerosis or osteoporosis (Hui et al., 1985; Rowland, 1996).
With respect to the potential regulatory benefits of physical activity, a strong rationale therefore exists for the advent of research which (1) complements that being undertaken in the physiological domain and (2) investigates the behavioural significance of adopting different activity approaches. In recognition of these needs, the aim of this study was to assess if differences in adolescent's MVPA participation occurred through the application of either a sustained or accumulated criterion. Reviews by Corbin et al. (Corbin et al., 1994) and Riddoch and Boreham (Riddoch and Boreham, 1995; ) intimate that differences may exist. In addition, a comparison of those studies which use either an EPM (Baranowski et al., 1987; Sleap and Warburton, 1994; Gilby and Gilby, 1995; Health Education Authority, 1997; Sallo and Silla, 1997) or C-LPAM (Verschuur and Kemper, 1985; Spurr and Reina, 1990; Suter and Hawes, 1993; Riddoch and Boreham, 1995; Myers et al., 1996) approach would suggest a disparity in activity status when different approaches are applied. However, this is the first study to undertake a concurrent comparison, which not only allowed investigation into whether differences were present, but also into why such differences may have occurred.
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Method |
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A convenience sample of 30 adolescents from an inner-city secondary school in the north of England gave informed consent to participate in the study (16 boys and 14 girls). Due to the level of validity and practicality such a measure provides (Montoye et al., 1996
; Armstrong and Welsman, 1997), children's physical activity was assessed using heart rate monitoring. Using Polar Vantage XL monitors (Polar Electro, Kempele, Finland), heart rate was recorded for a minimum of 3 full days (i.e. from 9.00 a.m. to 9.00 p.m. for 2 week days and 1 day at the weekend during the autumn). Following each day of assessment, monitors were collected, recorded heart rate data downloaded and then stored for analysis using Polar software.
Following heart rate monitoring in the field, the participants underwent a laboratory assessment. Height (Avery stadiometer, model S-769877), body mass (Seca analog scales, model 761) and skinfolds (tricep and subscapular; Harpenden calipers) were assessed. After a period of habituation, each adolescent undertook a continuous, incremental treadmill test (initial walking speed of 5 km/h at 0% gradient for 5 min, followed by a running speed of 8 km/h at 0% gradient for 3 min, with a 2.5% increase in gradient every 3 min thereafter). At each stage of the test, heart rate (CR7, Cardiorater, Germany) and oxygen consumption (
;O2: Oxycon Champion, Jaeger, Germany) values were recorded. Tests were continued to voluntary exhaustion with peak O2 and maximum heart rate scores also recorded. Using a physical activity readiness questionnaire, along with the measurement of blood pressure, each adolescent's suitability to undertake the treadmill test was reviewed prior to testing.
Analysis of heart rate data
Using recognized guidelines (American College of Sports Medicine, 1990) which relate physical activity intensity to a percentage of heart rate maximum (%HRMax), relative heart rate thresholds indicative of physical activity intensity were first established (i.e. light-to-moderate 35–59%HRMax, moderate-to-vigorous 60–79%HRMax, vigorous-to-heavy 80–89%HRMax and heavy 
90%HRMax). These thresholds were then applied to the collected heart rate data and physical activity participation assessed in two different ways.
Method 1 evaluated sustained physical activity whereby the number of adolescents who achieved three light+, moderate+, vigorous+ and heavy+ periods of sustained 5, 10 and 20 min duration were assessed. Method 2 evaluated accumulated physical activity whereby total energy expenditures (kcal/kg/week) within the classifications of light-to-moderate, moderate-to-vigorous, vigorous-to-heavy, heavy+ and moderate-to-vigorous-to-heavy+ physical activity were calculated.
Energy expenditures were estimated using daily heart rate data in conjunction with individual O2 heart rate regression equations generated from the data collected during the treadmill test. O2 was calculated for the midvalues of heart rate categories of 10 beats/min ranges (e.g. O2 for heart rate of 145 for the heart rate category 140–150). These values were then converted into energy expenditures using the assumption that for 1 l of oxygen consumed 4.92 kcal of energy were expended (Verschuur and Kemper, 1985). Weekday accumulated energy expenditures (i.e. Monday to Friday) were calculated by averaging weekday values and multiplying by 5. Weekend accumulated energy expenditures (i.e. Saturday or Sunday) were calculated by multiplying weekend values by 2. These weekday and weekend values were then added to produce an estimated weekly value.
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Results |
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A total of 25 adolescents fulfilled those criteria necessary for inclusion in heart rate analysis (i.e. at least 3 days of heart rate data of over 8 h duration). Table I
shows the mean ± SD for age, height, body mass and percent body fat [estimated from skinfolds using population-specific equations (Slaughter et al., 1988)].
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Based on an age-predicted maximum, mean maximum heart rate (HRMax: 201.8 ± 6.9 beats/min) suggested near maximal effort for the treadmill test. Mean peak
O2 score for the group was 47.5 ± 11.3 ml/kg/min while mean peak O2 scores for boys (56.9 ± 8.7 ml/kg/min) were found to be significantly greater (P < 0.001) than those for girls (38.1 ± 6.7 ml/kg/min). Mean monitored time for heart rate over 3 days was 11.04 ± 2.34 h/day.
Sustained physical activity
Table II describes the number of adolescents who could be classified as active when compared to sustained criteria (Method 1).
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All adolescents achieved the requisite durations of light+ activity. In regard to moderate+ activity, 10 adolescents failed to sustain three or more 5-min periods (4%), 12 failed to sustain three or more 10-min periods (48%), while 16 (64%) failed to meet the criteria advocated by the EPM (i.e. three or more 20-min periods of sustained MVPA). In relation to vigorous+ activity, 22 adolescents failed to sustain three or more 5-min periods (88%), 23 failed to sustain three or more 10-min periods (92%) and 24 failed to sustain three or more 20-min periods (96%). No adolescents achieved the requisite duration of heavy+ activity. Boys were consistently more active than girls, indeed all active subjects in vigorous + were boys.
Accumulated physical activity
Table III displays values for accumulated energy expenditure in respect to different activity intensities (Method 2).
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A total of 10 adolescents (40%) failed to meet those standards dictated by the C-LPAM (i.e. the accumulation of 42–56 kcal/kg of MVPA energy expenditure/week). Energy expenditure was found to consistently decrease with increases in intensity (light-to-moderate activity: difference of 57 kcal/kg/week, decrease of 60%, P < 0.001a, moderate-to-vigorous activity: difference of 30.6 kcal/kg/week, decrease of 80%, P < 0.001b and vigorous-to-heavy activity: difference of 2.7 kcal/kg/week, decrease of 35%, P < 0.01c). Total moderate, vigorous and heavy activity energy expenditure for boys and girls showed boys to be more active than girls (difference of 17.1 kcal/kg/week). A significant sex difference in energy expenditure was found for vigorous activity (difference of 7.1 kcal/kg/week, P < 0.05d).
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Discussion |
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The results illustrated in both Tables II and III
support suggestions that a large increase in young people's physical activity occurs with decreases in intensity (Riddoch and Boreham, 1995). However, the value of such participation is debatable in that the benefits of low intensity physical activity are at present somewhat speculative (Health Education Authority, 1998). In addition, results also support suggestions that boys are more active than girls (Physical Activity Task Force, 1995). This was a finding consistent for both models and was evident through all intensity classifications.
In respect to the main aim of this study, findings clearly demonstrated a difference in adolescent MVPA participation with the application of different approaches. As Figure 1 illustrates, based on a 3-day monitoring period, the use of a sustained criterion resulted in the minority of adolescents being classified as active (nine children or 36% of the group). However, by using an accumulated criterion over the same period of time, the majority of adolescents were found to be active (15 individuals or 60% of the group). Such a finding supports the suggestion made by both Corbin et al. (Corbin et al., 1994) and Riddoch et al. (Riddoch et al., 1995), that young people are generally more active when judged by C-LPAM standards than when judged by EPM standards.
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As intimated earlier in the introduction, the concurrent nature of the comparison undertaken by this study allowed investigation into why such differences may have occurred. Analysis indicated that six adolescents (or 24% of the group), while unable to meet the sustained dictates of the EPM, were able to meet the accumulative standards of the C-LPAM. Further analysis of EPM data by 20, 10 and 5 min duration (Figure 2
) indicated that, as duration of sustained MVPA decreased, the participation rate of these adolescents increased. Indeed, a decrease in duration from 20 to 10 min of sustained MVPA resulted in four of the six previously inactive adolescents now being able to be classified as active (an increase of 16%). A further decrease in duration to 5 min resulted in the remaining two adolescents being classified as active (an additional increase of 8%).
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This increase in participation with a decrease in duration is also evident in a cross-examination of the literature. The findings of Armstrong and Welsman suggested that only 20% of British adolescents recorded a 20-min sustained bout of MVPA in a week (Armstrong and Welsman, 1997
). Salo and Silla; however, using a 10-min activity duration found 40% of American adolescents to be active (Salo and Silla, 1997). Indeed, Armstrong and Welsman, by lowering duration of sustained MVPA further to 5 min, found an additional increase in that 73% of adolescents could now be classified as active (Armstrong and Welsman, 1997). Taken with the findings of this study, such evidence would seem to indicate that the reason why a number of young people are more active when judged by C-LPAM as opposed to EPM standards, resides with the lower levels of MVPA duration such a model prescribes.
Such a suggestion has important implications for practitioners who prescribe physical activity, in that, while a number of adolescents seem unable to achieve recommendations which advocate long-duration, sustained MVPA, they do seem to be able to achieve recommendations which advocate the accumulation of short duration MVPA. For such adolescents, it may therefore be suggested that, from the perspective of establishing a regular activity habit, the application of the C-LPAM may be more behaviourally viable. This may be due to the short duration MVPA such an approach prescribes, which more accurately reflects the sporadic, spontaneous nature of young people's natural activity behaviour. Indeed, in a detailed observational study of 15, 6–10 year olds, Bailey et al. indicated that the tempo of young people's physical activity is one of rapid change, in that it consists of short transitions of intense activity interspersed with varying intervals of low-to-moderate intensity activity (Bailey et al., 1995). Such findings would seem to support the suggestion that the prescription of accumulative MVPA consistent with the C-LPAM may be more ecologically valid than the application of the sustained, prescriptive exercise regime dictated by the EPM. In addition, it should also be recognized that the findings of this study identified a large minority of adolescents (10 individuals or 40% of the group) who were inactive when judged by both the EPM and C-LPAM. The suggestion that an accumulative approach may more accurately reflect young people's daily life experiences, would intimate that practitioners may wish to initially consider adopting a C-LPAM rather than EPM philosophy in seeking to counter young people's inactivity. Indeed, such an approach may be suggested to circumvent those perceived barriers to participation, (i.e. low ability, achievement and success) which the habitually inactive unavoidably erect when confronted with a prescriptive exercise regime.
In conclusion, it is important to acknowledge that the findings of this study are based on data taken from a relatively small sample who were assessed over a relatively short duration of time. However, it is also important to recognize that small numbers are an endemic problem when measuring physical activity objectively and, indeed, should be balanced against the fact that, if used effectively, such techniques are able to provide highly detailed information. In addition to this, while Trost et al. recently suggested an ideal monitoring period of 7 days (Trost et al., 2000), Armstrong and Welsman indicate that if a weekend day is incorporated, 3 days adequately reflects typical behaviour (Armstrong and Welsman, 1997).
While further research is therefore needed which utilizes larger numbers over a longer monitored period, the findings of this study may still be regarded as providing valid insights. Such would suggest that, for the majority of young people, the application of a C-LPAM rather than an EPM approach may be more viable in establishing an activity habit which influences life-long participation. This may be due to the fact that such activity more accurately reflects these young people's everyday experiences. It should be recognized that such a suggestion does not indicate that the EPM is behaviourally unsuitable for all young people. Indeed, as the findings of this study also relate, for some, sustained MVPA may be highly effective at promoting habitual participation. Rather, it indicates that, regardless of whether an EPM or C-LPAM philosophy is adopted, the physical activity practitioners prescribe should be suited to the individual and compliant with their environmental, biological and psycho-social profile. Future research may therefore wish to consider how variables such as facilities, body composition and cardiovascular fitness, familial aggregation or physical self-perceptions relate to those different activity approaches young people's guidelines currently advocate.
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Received on May 19, 2000; accepted on November 11, 2000
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