The practice of physical activity (PA) is essential for promoting health and well-being, as it is associated with numerous benefits, including reduced risk of chronic diseases like cancer and cardiovascular disease, improved cognitive function, decreased depressive symptoms, and lower mortality.1–4 These health benefits are widely recognized by global health organizations, which have established guidelines to encourage physically active lifestyles.5,6

However, despite evidence of the benefits of PA and ongoing efforts to promote its regular practice, it has been observed that the Brazilian population between 55 and 64 years of age has a prevalence of physical inactivity of ∼49 % and for those over 65 years of age of ∼63 %,7 opting for a more sedentary lifestyle.8 Sedentary behavior (SB), characterized by activities such as sitting or reclining with energy expenditure ≤1.5 METs,9 is associated with adverse health outcomes,10 including increased mortality risk and reduced life expectancy.11,12

Addressing the challenge of promoting behavior change in older adults requires exploring strategies that effectively enhance health and well-being. In this sense, isotemporal modeling11,13,14 emerges as a promising approach that, through a widely used mathematical model, provides insights into how the reallocation of time devoted to SB to different domains of PA15–19 can influence health and longevity, through a widely used mathematical model, test the most effective way to reduce harmful health risks, and help to develop more insightful strategies to improve health and longevity.20–23 Behaviors are known to be synergistic, and increasing or decreasing one behavior can directly affect the exposure time of the other.11,24

Recent scientific literature shows an association between the practice of PA, especially that performed during leisure time, and the health of the older adult population.15,16,18 However, the relationship between PA in the occupational context and health outcomes is still the subject of debate, with studies indicating both beneficial and harmful effects depending on the intensity and duration of the activity,16,25–27 while in other contexts and domains it is still unclear, but worse, a certain positive influence on mortality risk between the transport and domestic domains. This ambiguity highlights the need for more in-depth research that can elucidate the nuances of the relationships between the different domains of PA and their specific impacts on health and mortality in older adults.

Therefore, the aim of this study was to examine the potential effects of replacing time spent on SB with PA in different domains on mortality risk in Brazilian older adults. We hypothesized that such a substitution could lead to a significant reduction in mortality risk, thus reinforcing the importance of PA as a key determinant of health and longevity in old age. This study will not only contribute to the understanding of the relationship between PA, SB, and health in the older adult population, but will also provide valuable evidence for the development of public policies and interventions aimed at promoting active and healthy lifestyles among older adults.

Of the 332 study participants, the majority were female (63.6 %) and retired (68.1 %), the average age was 71.0 years (SD 8.5 years), the total loss in the segment was ∼30 %, other descriptive information is described in Table 1.

The daily average times of the activities included in the Isotemporal model were 8.47 min/day (SD 1.96 min/day) of occupational PA, 18.94 min/day (SD 2.08 min/day) of domestic PA, 7.95 min/day (SD 0.89 min/day) of leisure-time PA, 435.00 min/day (SD 107.00 min/day) of sleep, and 436.50 min/day (SD 9.08 min/day) of SB. Table 2 presents the mean times, median, standard deviation, interquartile range, and deltas according to vital status.

The isotemporal substitution model is presented in Table 3. At all times tested in the model, replacing the time of exposure to SB with PA in the leisure domain proved to be a protective factor for the risk of mortality among participants. Conversely, the inverse replacement was demonstrated to be a risk factor for mortality, with risks varying between HR=1.42 (95 %CI: 1.01, 20.2) for 10 min and HR=8.32 (95 %CI: 1.01, 68.64) for 60 min, suggesting an increase in mortality risk with increasing time.

Our main objective in this study was to verify the hypothetical effects of replacing SB exposure time and PA domains on the risk of mortality in older adults. We observed that reallocating sedentary time to an equivalent duration of PA in the leisure domain reduced the risk of mortality in older adults by 30 % to 78 % for reductions of 10 min and 60 min, respectively. Conversely, opposite substitutions, reducing leisure time and increasing sedentary time, increased the risk of mortality. Therefore, although we did not observe a reduction in mortality risk when substituting sedentary time across all domains of PA, we can confirm our study hypothesis.

The implications of our results are manifold and echo existing literature highlighting the health benefits of regular PA for older adults in reducing mortality risk.3,4,33,34 In addition, the model's emphasis on isotemporal substitution provides a new perspective for examining the relationship between different types of activity and health outcomes. It suggests that not only increasing PA, but also reducing sedentary time, is critical for health, particularly among older adults. This dual approach is consistent with the World Health Organization guidelines, which advocate both increasing PA and reducing sedentary time to improve health outcomes.5

In our study, replacing SB time with leisure-time PA was shown to reduce the risk of mortality in older adults, as demonstrated in other studies.15,16,18 Arem et al.15 compared mortality risk in relation to leisure-time PA and found that meeting the proposed PA recommendations (7.5 to <15 MET h/week) reduced mortality risk by ∼31 %. However, increasing this time in search of additional benefits showed a ceiling effect when performing between 3 and 10 times the recommended amount (22.5 to <75 MET h/week), resulting in a 39 % reduction in mortality risk. In other words, leisure time appears to contribute to a reduction in mortality risk, thereby increasing population survival.

Although our study did not show an association between the duration of occupational PA and mortality risk, other studies have shown trends in these variables.16,25–27 They suggest that longer duration or higher intensity of occupational PA may increase mortality risk.26,27 In addition, longer periods of occupational PA are associated with a higher risk of disability leave.35 However, some studies have failed to find an association with mortality, possibly due to factors such as intensity and sex.17,36

Possible mechanisms explaining the associations between health outcomes and the domains of occupational and leisure-time PA are discussed by Holtermann et al.37 The authors note that leisure-time PA typically involves high-intensity, short-duration, dynamic activities with ample recovery time, whereas occupational PA tends to be moderate to low-intensity, prolonged, and involves static movements with limited recovery. However, the lack of association in our study may be due to the low participation in occupational PA among the older adult participants, as the majority are retired or not in paid employment.

Furthermore, it is important to emphasize that leisure-time PA is not only more intense, but also often associated with a greater sense of enjoyment, satisfaction, and subjective well-being. This makes the transition from time spent on SB to leisure-time PA potentially easier compared to other domains of PA.38,39 This observation is particularly relevant in the occupational context, where interventions and promotion of PA may be more effective if specifically targeted at the leisure domain. Therefore, understanding and mastering intervention strategies that promote participation in leisure-time PAs may be a valuable tool for health and disease prevention professionals.

Because work is an inescapable aspect of human life, a recently published systematic review sought to investigate whether leisure-time PA might have beneficial effects in workers with different levels of leisure-time PA.40 The review observed that in individuals with low levels of occupational PA, increased leisure-time PA conferred protective effects. However, these effects were not observed in workers with moderate or high levels of occupational PA.40

In contrast to PA, SB is consistently associated with health risks, including a higher risk of mortality.3,11,34 Our study revealed that replacing leisure-time PA with sedentary time increased the risk of mortality. Galvão et al.11 observed a 35 % increased risk of mortality when replacing 30 min/day of moderate-to-vigorous PA with the same amount of sedentary time, with this risk potentially increasing to 82 % when replacing 60 min/day. Reducing sedentary time in favor of PA, regardless of intensity, may reduce mortality risk.34

In addition to total sedentary time, several specific domains of SB have been associated with increased mortality risk.41,42 For example, each additional 30 min of screen time per day is associated with a 1 % increased risk of mortality.41 These findings underscore the significance of not only assessing the total sedentary time but also investigating different SB and their individual consequences on health and longevity.

Although we did not include sleep duration in our analyses because we consider this to be adequate in the older adults studied, we recognize its importance in mortality risk. Currently, the ideal amount of sleep is approximately seven hours per night.43,44 Studies have shown that individuals with chronic diseases who sleep less than seven hours or >10 h have an increased risk of cardiovascular events, with risks increased by 42 % and 85 %, respectively.43 In another cohort of Asian participants, also using the seven-hour sleep reference point, the risk of mortality was increased in participants with less than five and more than eight hours of sleep per night.44 Therefore, individuals with irregular sleep patterns are at increased risk of mortality.

Given that the day is limited to 24 h, behaviors must be directed to maximize efficiency and obtain the greatest benefit, with the ultimate goal of increasing longevity and reducing the risk of mortality. This notion is supported by an accelerometer-based cohort study of >92,000 participants with an average age of 62 years.45 The results show that regular PA reduces the risk of mortality associated with sleep patterns that are considered detrimental to health.45

PA practice in the transport domain may be associated with a lower risk of mortality, as shown in a cohort study of 10,853 individuals with a mean age of 47.9 years and non-alcoholic fatty liver disease. However, these benefits seem to be more pronounced in individuals who practice more activity in this domain (>299 min/day), as well as in the leisure domain. On the other hand, practicing activity in the occupational domain seems to have no effect on mortality risk.21

This finding corroborates a cohort study carried out on the population of Peru, which included 3601 people with an average age of 55.8 years. The participants were divided into two groups according to their PA in transport: a group with less PA and a group with more PA. It was found that participants who were physically active in this area had a 42 % lower risk of death than those who were less active.46 Although we didn't observe reduction in mortality risk in this transport domain in our older participants, this difference could be due to our subjective assessment method, the sample size or the short period of practice in this domain.

The practice of PA in the domestic sphere can be confused in some cases with the practice in the work sphere, to the extent that in many cases it becomes something obligatory rather than enjoyable. In addition, a certain level of effort in this practice may reduce the risk of mortality.22,23 When evaluating the Italian population, mortality risks were only reduced among men with moderate PA practice in the domestic domain, compared to those who do not practice, and no associations were observed between those with low or high practice time in this domain, nor among female participants.23 This is supported by another study involving the Taiwanese population, which found only positive associations with moderate PA practice in the domestic domain.22 However, PA in the home domain appears to be associated with a lower risk of accelerated aging although it does not always reduce the risk of all-cause respiratory or cardiovascular mortality in participants with chronic obstructive pulmonary disease over 40 years of age.22,23,47

• Our study has limitations, including the use of self-reported measures, which may introduce recall bias. However, we mitigated this issue through prior training of the data collection team. Additionally, we experienced a segment loss of ∼30 % of the sample. Furthermore, while the isotemporal substitution model is widely accepted and disseminated, it remains a hypothetical mathematical model, and its findings may not fully reflect real-world consequences of substitutions. Moreover, the low distribution of PA across specific domains may compromise interpretations. Small number of events and limited sample size. Therefore, future studies should address these evidence gaps and explore relationships between specific SB, such as screen time on TV, computer, or mobile phone, to elucidate more complex associations between behavioral substitutions.

• As strengths, we highlight the use of a representative sample with a five-year follow-up period, located in a city with a low human development index within a developing country. In addition, our study used specific domains of PA practice, recognizing that each domain may have different effects on outcomes. For example, leisure-time PA has been shown to reduce mortality risk.

• Public policy should prioritize the promotion of regular PA, particularly among older adults, with a focus on leisure-time activities. The large body of evidence supporting the benefits of leisure-time PA in reducing the risk of mortality and adverse outcomes underscores the importance of such initiatives. Specific activities such as tennis, soccer, and cycling have been shown to increase life expectancy by 9.7, 6.2, and 3.7 years, respectively.48

In our isotemporal replacement model, a significant reduction in mortality risk was observed in older adults during a five-year follow-up period when sedentary time was replaced for the same amount of leisure-time physical activity. Conversely, the opposite substitution, reducing leisure time and increasing sedentary time, increased the risk of mortality.

During the preparation of this work the author(s) used ChatGPT from OpenAI to assist in translating this article. After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication.