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Physical activity (36 minutes) moderates the effect of sedentary time on an older adult's physical independence
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Background/objectives
Moderate-to-vigorous physical activity (MVPA) and breaks in sedentary time (BST) have been proposed as viable solutions to improve an older adult's physical independence, whereas sedentary time (ST) has been associated with detrimental effects. We sought to assess the joint effects of ST, BST, and MVPA on the physical independence of older adults and determine whether and to what extent the ST relationship with physical independence is moderated by MVPA and/or BST.
Participants
Older adults (≥65 years old) from the national surveillance system in Portugal (n = 821).
This study shows that performing ≥36 min of MVPA [moderate-to-vigorous physical activity]per day can offset the detrimental effects of ST on an older adult's physical independence. Thus, public health policies should primarily target strategies to improve levels of MVPA and, secondly, reduce ST, to promote a healthy aging process.
In conclusion, MVPA moderated the relationship between ST and an older adult's physical independence, such that performing >36 min/day of MVPA eliminated the negative association of ST. Moreover, performing >108 min/day of MVPA promoted a positive association between ST and physical independence, indicating that for highly active older adults, ST may be beneficial for one's ability to maintain physical independence. For older adults who struggle to perform sufficient amounts of any type of PA, decreasing ST and increasing MVPA by any incremental amount should not be overlooked as a viable strategy to improve healthy aging.
Our investigation suggests that higher amounts of ST were related to lower values of physical independence, regardless of time spent in MVPA and BST. However, the nature of the relationship between ST and physical independence became non-significant when older adults engaged in ≥36 min/day of MVPA. No moderation effect was observed for BST on the relationship between ST and physical independence.
In this investigation, we have shown that performing 36 min/day of MVPA can offset the negative effects of ST on an older adult's physical independence. Other studies in older adults have also come to similar conclusions regarding the moderating effect of MVPA on the relationship of ST with frailty10 and mortality.11, 17-19 Mañas et al.10 found that 27 min/day of MVPA eliminated the negative association between ST and frailty in older adults. Although we used a similar statistical approach and our samples had similar characteristics in terms of age, sedentary time (491.4 min/day from our study vs. 538.7 min/day from Mañas et al.10), and levels of MVPA (median: 9.3 min/day or mean: 17.1 min/day vs. mean: 19.7 min/day from Mañas et al.10), Mañas et al.10 found a lower cutpoint compared to ours which may be related to the different outcomes assessed. Considering the outcome of all-cause mortality, Ekelund et al. reported that 60 min/day of moderate PA17 or 30–40 min/day of MVPA11 were needed to attenuate the adverse association of sedentary behavior using subjective and objective PA data, respectively. Overall, based on our results and those of Mañas et al.10 and Ekelund et al.,11, 17 it seems that the amount of MVPA needed to offset the harmful effects of ST depends highly on the health measure examined, as well as on the assessment method for acquiring PA information.
Interestingly, we observed that beyond ~108 min/day of MVPA, ST was positively related with an older adult's ability to be physically independent. This finding is potentially related with certain benefits specific domains of sedentary behavior may provide in terms of rest and recovery. In fact, a prospective cohort study observed that women who met the PA guidelines (≥450 MET × min/week) and reported sitting the most (≥11 h/day) actually had a reduced mortality risk compared to the other women who met the guidelines and had less sitting time.18 However, it is important to note that only a small portion of our sample had MVPA levels >108 min/day. More studies including a greater number of individuals falling within the upper end of the MVPA spectrum are needed to verify if ST can be beneficial for older adults who perform high levels of activity throughout the day.
INTRODUCTION
Having a physically active lifestyle is considered a key strategy to prevent the loss of physical independence and promote a healthy aging process in older adults.1, 2 Beyond physical activity, epidemiological and experimental evidence have also identified sedentary time (ST) as a predisposing risk factor for health outcomes related to functional disability, reduced functional capacity, and frailty in older adults,3, 4independent of time spent in moderate-to-vigorous PA (MVPA). In fact, several investigations have highlvighted the importance of interrupting the time spent in sedentary behavior by performing regular breaks of PA5-9 to improve the physical independence and function of older adults.
Much of the prior literature has not examined the joint and interacting effects of MVPA and breaks in sedentary time (BST) with ST. Thus, the question of whether individuals can overcome the detrimental effects of ST if they undertake higher amounts of MVPA or BST remains to be fully answered. It has recently been reported that 27 min/day of MVPA were needed to offset the harmful effects of ST on frailty in older adults,10 and between 30 and 40 min/day of MVPA were needed to eliminate the increased risk of premature death associated with ST in middle to older aged adults.11 Currently, the extent to which MVPA and/or BST may influence the effect of ST on the risk of physical dependence in older adults has not been investigated.
The aims of this investigation were twofold: (1) assess the joint effects of objectively measured ST, BST, and MVPA on the physical independence of older adults; and (2) to determine if the relationship of ST with physical independence is moderated by MVPA and/or BST.
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