The present systematic review aims to provide a synthesis of studies that have analyzed changes in overall PA, assessed using objective measurements, or compensatory behavior caused by PA increases or decreases in a specific PA domain or during the time-span of a day in children and adolescents.
A total of 77 articles were included that investigated compensation or displacement across various contexts in children and adolescents. Overall, approximately 50% of the included articles found indicators suggesting compensation and 50% refuted compensational behavior and supported displacement of inactive time with bouts of activity. Detailed analyses based on study design, target group, instruments, context, intervention duration, and measurement duration were performed, revealing differences in compensation depending on categories. The analyses showed tendencies toward compensation in school interventions (especially with durations lasting longer than 1 year) and tendencies of displacement in the context of weekly-organized participation in sport clubs.
It is hypothesized that when PA in one domain or time-span increases, PA in another domain or time-span decreases in order to maintain the PA level constant, as postulated by the ActivityStat hypothesis [27]. In the present analysis, 38 of 77 articles, including 24,532 participants, refuted the ActivityStat hypothesis and showed an increase in overall PA that resulted from imposed PA in one domain or time-span and absence of a reduction in PA in other domains or time-spans. Sustained displacement of inactivity with PA led to an overall increased PA level, as described in the displacement hypothesis. One possible explanation for these increases in overall PA could be that imposed PA stimuli serve as some kind of trigger: PA opportunities in different contexts may stimulate children and adolescents to engage more in physical activities during the entire day [67, 73, 81, 93-95].
In our review, we distinguished between interventional and non-interventional studies. A total of 21 interventional studies (N = 6,477 participants) showed indicators for compensation, whereas only 18 non-interventional studies (N = 9,820 participants) indicated compensatory behavior. This suggests that when PA of children and adolescents is promoted in an intervention, the participants tend to compensate for the additional bouts of PA within the intervention by decreasing their activity levels during other parts of the day or in other domains so that they maintain their overall PA at a stable level. On the other hand, when children increase their PA levels on their own, without participating in an intervention program (in non-interventional studies), it seems that they do not compensate for this and ultimately increase their overall PA level. This could be due to the fact that, in these cases, their PA is more likely based on intrinsic motivation that external influences. Furthermore, interventions were mostly offered and performed in (pre)school contexts. Improvements in (pre)school PA can be compensated for by less PA outside of (pre)school [36, 37, 55, 56, 59, 62, 64, 66, 77-79, 96-103]. “It is possible that school-based interventions are too focused on school setting and children and adolescents do not translate the health message on the importance of physical activity at home or in the community” [15]. For school interventions, it has been suggested that the focus should also be placed on changing parental behaviors and awareness for the sake of adopting a sustainable active lifestyle. In addition, multicomponent interventions or interventions that include schools together with families or communities are most effective in changing PA levels [15, 35]. In general, interventions are most efficient when they operate on multiple levels [104]. “According to ecological models, the most powerful interventions should (a) ensure safe, attractive, and convenient places for physical activity, (b) implement motivational and educational programs to encourage use of those places, and (c) use mass media and community organization to change social norms and culture.” [105]. Since intrapersonal, interpersonal, organizational, community, and public policy factors can influence health behaviors, they consequently counteract compensatory behavior. Despite the fact that the literature suggests that multicomponent interventions have been shown to be useful for changing PA behavior, our results contradict this assumption by the findings of compensatory behavior in all multicomponent studies [36, 37, 77, 79, 102, 103].
Analysis of interventions pointed out a wide range in terms of intervention duration. All six studies (N = 2,541 participants) in which interventions lasted for over one year supported compensation behavior in children and adolescents [36, 55, 56, 64, 77, 78]. Nevertheless, compensatory behavior in children and adolescents was also identified in interventions that had a duration between one month and one year [37, 62, 68, 75, 79, 96-98, 100, 101, 103]. A possible explanation for this finding could be that interventions that last for a shorter period of time may have no or less effect in changing the PA behavior of children and adolescents due to a lack of time needed to progress through the six stages of change, according to the trans-theoretical model [106]. This means that children and adolescents who accumulate more MVPA during an intervention might continue to be as physically active in their leisure time as they were before the intervention. The longer an intervention lasts, the greater the probability that children and adolescents would adapt their PA and become less active in their leisure time—hence, maintaining their overall PA at a stable level.
Almost all studies included in our review captured PA data using pedometers or accelerometers. Six pedometer studies (N = 6,938 children and adolescents) reported compensatory mechanism [37, 75, 79, 82, 84, 88], whereas children and adolescents (N= 9,309) showed compensatory behavior in 32 accelerometer studies [36, 55-59, 62, 64, 66-69, 71, 76-78, 80, 81, 83, 85-87, 89, 91, 96-103]. One explanation for this finding could be that pedometers only capture step counts—an index of the number of steps a person took—whereas the overall PA levels for participating individuals remained unknown. Hence, it is likely that compensation is diagnosed through a measured reduction in steps, while other shifts in PA levels (e.g., overall MVPA) remain unconsidered. Furthermore, only one study out of the 77 analyzed studies investigated energy expenditure using a heart rate monitor and indicated compensation [107].
Besides interventions in a school context, there are two other settings in which children and adolescents are physically active. Only 57% of children and adolescents who actively commute to school showed indicators for compensation [81, 83, 84, 86]. Active commuting and independent mobility of children provide additional opportunities for spontaneous play [95] and enable other active behaviors [108, 109]. This can lead to an increase in overall PA and, therefore, supports the displacement theory.
In the PE context, only 32% of the participants indicated compensatory behavior [67, 71, 82, 88, 89, 91]. PE classes should provide an opportunity for children and adolescents to engage in PA and to develop knowledge about and attitudes toward developing an active lifestyle [110], which could lead to displacing inactivity with active behavior. Interestingly, two articles, involving 365 participants, investigated the impact of different amounts of PE per week on overall PA levels in children and adolescents. From their findings, it can be summarized that more PE per week is not necessarily effective for increasing total PA because the PA in PE classes is often compensated for by less activity outside of the school setting [71, 89]. Consequently, future studies should assess what the right amounts and intensities of PA during PE classes would be in order to avoid compensation outside of school.
Finally, our detailed analyses reveal one PA domain in which an increase of activity levels was not found to lead to compensation but, instead, to displacement: when engaging in organized sport clubs, children and adolescents do not compensate their PA levels by being less active after the training sessions [61, 63, 111-113]. Sport clubs represent a health-promoting setting and support children and adolescents in living an active lifestyle outside sport clubs [114]. Furthermore, sport programs can provide beneficial access to and resources for recreational activities [112]. Thus, participation in sport clubs serves as an additional factor for increasing overall PA and can displace sedentary behavior.
Compensatory behavior occurs after a PA increase or decrease in one domain or time-span in order to maintain a stable overall PA level. Almost all studies in this review revealed that a PA increase in one domain or time-span is followed by a PA decrease in another domain or time-span, which is negatively connoted. Nevertheless, there exists one study [82] in our review, where compensatory behavior was found to occur after a PA reduction—leading to compensation being positively connoted.
4.1 Implications
This review of compensation for PA in children and adolescents provides inconsistent results relating to compensation. Consequently, further research is needed for better understanding of compensatory mechanisms and a recommendation is made for future studies to investigate PA behavior over a period of a few days using an objective measurement method. In addition, participants should complete a questionnaire or keep a diary in order to terminate and locate their activities and to obtain information about the reasons for their PA behavior. Social support plays an important role for sufficient PA in children and adolescents. Thus, PA behavior and attitude of family and friends can influence one’s own PA and determine compensatory behavior. Additional subgroup analysis, including an examination of differences in PA by gender, age, weight status, socio-economic status (SES), and ethnicity, could provide more information about compensatory behavior. Gender differences have already been seen in a few of the included studies with inconclusive results [59, 67, 81, 83]. Additionally, various SES analyses indicate different environmental, social, and educational circumstances [115, 116]. Hence, SES is an important predictor of PA in children and adolescents [115] and can influence compensatory behavior. Unfortunately, none of the included studies investigated compensatory behavior separately for different SES. It is hypothesized that children and adolescents with lower SES compensate more often than individuals with higher SES. It would also be interesting to further investigate the setpoint for “ActivityStat” or possible differences depending on age, season, or energy intake. With the help of an experimental design, future studies could investigate when this setpoint is reached and whether there are differences. Furthermore, there are currently no existing theories that deal with the timeframe for compensation. It is hypothesized that the timeframe for compensation is unlikely to be day-to-day [27]. Currently, the timeframes in the studies examined in our review are random. Finally, combined measurement of energy expenditure and PA should be used to obtain more detailed and reliable information about compensatory mechanisms.
Practical implications refer to interventional studies: besides active PA promotion, it is important to improve the awareness in children and adolescents, as well as in their parents, regarding the importance of PA as well as to enable them to be physically active at home during their leisure time. This is necessary in order to avoid compensation that occurs when PA at home and/or in the family environment is reduced after increases in PA levels take place during interventions in, for example, the school setting.
4.2 Strengths and limitations
The main strength of this review is that we exclusively included studies that objectively measured PA, including measures that directly assessed one or more PA dimension (e.g., frequency, intensity, time, type) and captured a variety of measures, such as step counts, activity minutes, and PA intensity [117]. An additional strength lies in the fact that the systematic search of relevant primary studies employed several electronic databases and a comprehensive list of search strings. Furthermore, the reference lists of all included studies were manually checked in the search for additional relevant studies. Our search strategy was broad enough to allow us to identify relevant studies as well as to include those studies that did not analyze PA compensation as their main objective. In contrast to Gomersall et al. [27], we did not only include studies that made explicit reference to compensation. Instead, we analyzed studies investigating changes in overall PA and in different domains or time segments for compensatory mechanisms. Another strength is the inclusion of a wide range of different settings in which PA plays an important role.
A limitation of this review relates to the variety of the study designs of the included studies, which made a comparison of the results difficult. Additionally, some studies only allowed between-subject analyses, which, in turn, only enabled conclusions about compensation to be obtained from a comparison of PA levels between two groups. For better understanding of compensatory mechanisms, within-subject analyses provided stronger results. Another limitation is that there were different PA segments in the reviewed studies, which made it difficult to compare them all.