Sedentary behavior and its pattern are associated with postural balance and fear of falling in asymptomatic adults: a cross-sectional study

Objective: Sedentary behavior (SB) is an independent predictor of all-cause mortality when compared to moderate-to-vigorous physical activity (MVPA). However, the influence of SB on the fear of falling (FOF) has not been investigated. We aimed to evaluate the association of SB and FOF in middle-aged and older adults. We conducted a cross-sectional study. FOF was achieved through the International Fall Efficiency Scale. SB and MVPA were obtained using triaxial accelerometers. Multiple linear regressions were performed to verify the association between SB, MVPA and FOF. Results: 75 middle-aged and older adults participated to the study. Sedentary breaks presented a more important role than the sedentary bouts and the MVPA in FOF. The SB and its pattern present a determinant association with postural balance and FOF in middle-aged and older adults. Hence, our findings reinforce the importance of middle-aged and older adults to perform the recommended amount of MVPA to maintain postural balance and reduce FOF.


Introduction
High rates of falls represent a public health concern not only for the older adults, but for subjects of all ages [1]. Overall balance performance begins to decline after the 5th decade of life, which related to an inactive lifestyle and other physiological changes may lead to reduced physical performance and increased risk of falls [2,3].
Older adults present fear of falling (FOF), which is strongly associated postural instability [4] and directly related to gait problems, reduced muscle strength, psychological factors and restriction of activities of daily living [5]. Subjects with FOF become more cautious, reducing PA and resulting in increased joint stiffness [6,7]. 3 SB is any waking behavior with energy expenditure ≤ 1.5 metabolic equivalents of task (METs) or the adoption of sitting and reclining postures. SB lifestyle raises the risk of diabetes, cardiovascular diseases and early mortality [8,9].
Additionally, aging result in increased SB and less sedentary breaks [10], which can contribute to physical deconditioning and inactivity and may lead to fragility, falls and loss of independence [11]. All these factors can be reduced by interrupting SB [12,13]. However, just a few studies directly relate SB with FOF and postural balance [14,15].
We hypothesized that SB is associated with the FOF and postural balance in middle-aged and older adults. Thus, we aimed to evaluate the association between SB and its pattern and the FOF and postural balance in asymptomatic adults.

Methods
We conducted a cross-sectional study with participants selected from the Epidemiological Study of Human Movement (EPIMOV Study). Briefly, the EPIMOV Study is an epidemiological cohort study with the main purpose of investigate the longitudinal association between SB and physical inactivity and development of hypokinetic chronic diseases [16,17]. Exclusion criteria for the EPIMOV study were: regular use of gaiters and/or difficulty performing physical exertion due to osteoarticular problems, recent respiratory infections, unstable or stable angina in the last four weeks, recent myocardial infarction, angioplasty or cardiac surgery in the last three months.
For the present study, participants aged 40 years or over were considered eligible. Middle-aged and older adults were eligible because the prevalence of falls, as well as rates of chronic diseases and use of medication, has increased 4 from this age group [1,18,19]. All procedures were explained to the participants and they signed a free and informed consent form. The EPIMOV Study was approved by the local Research Ethics Committee(# 186.796).

Clinical evaluation
At first, we inquired the participants about previous health problems and medication use. Cardiovascular risk was based on the following factors: age, family history, smoking, hypertension, dyslipidemia or hypercholesterolemia, diabetes mellitus or hyperglycemia, obesity and physical inactivity [20]. We also questioned the use of medication, and if so, which ones since sleeping pills, antidepressants, and polypharmacy are predictors of occurrence of falls.

Cardiorespiratory fitness
We performed a cardiopulmonary exercise testing on a treadmill (ATL, Inbrasport, Porto Alegre, Brazil) using an individualized ramp protocol until exhaustion. Oxygen uptake (V'O 2 ), carbon dioxide production and minute ventilation were monitored throughout the test using a gas analyzer (Quark PFT, Cosmed, Pavona di Albano, Italy). The heart rate was continuously monitored during the CPET by means of a 12 lead ECG. The average value of the V'O 2 (ml/min/kg) during the last 15s was representative of the peak V'O 2 (i.e., cardiorespiratory fitness) [21].

Physical activity and sedentary behavior
The PA and SB were assessed by using a previously validated triaxial accelerometer (GT3X ActiGraph, MTI, Pensacola, Florida, EUA) [22].
Participants were instructed to use the device for seven days on their dominant hip. One day is considered valid if participants use the device for at least 12 hours [23]. The data of the participants who used the accelerometer for at least four valid days for at least 12 consecutive hours per day were analyzed [24]. 5 We considered SB as activities with less than 100 counts per minute (cpm) or energy expenditure ≤ 1,5 MET. The time of non-use was defined as at least 60 consecutive minutes of 0 counts (i.e., 0 to 99 cpm). The sedentary bouts were considered as less than 100 cpm for at least 5 minutes, whereas the sedentary breaks were considered as more than 100 cpm (i.e., sedentary time to active time) [23].
We obtained the amount and intensity of weekly PA levels, as follows: light (≤3.00 METs or between 100 and 1951 cpm), moderate (3.00 to 5.99 METs or between 1952 and 5724 cpm), vigorous (6.00 to 8.99 METs or between 5725 and 9298 cpm), very vigorous (≥ 9.00 METs or> 9499 cpm) [24]. The minimum level of PA was considered as 30 minutes daily moderate-to-vigorous PA (MVPA) for at least five days per week. Participants who did not reach this level of PA were considered physically inactive [25]. The data selected were the total and average sedentary bouts, as well as their maximum and minimum durations, total and mean sedentary breaks, total sedentary time, and levels of PA (i.e., light PA, moderate PA, MVPA, vigorous PA, very vigorous PA).
Then, we calculated and selected lean body mass and fat body mass as absolute value and as percentage to further analysis [28].

Fear of falling
We evaluated the FOF through the International Falls Efficiency Scale (FES-I).
For each activity daily living, there is a score of 0 to 4, respectively very 6 confident and not at all confident. The score can range from 16 to 64. When closer to 64, greater the FOF [29,30].

Postural balance
We evaluated static and dynamic postural balance, respectively using a force platform (BIOMEC 400, EMGSystem, Brazil) and the Timed Up and Go (TUG) test and the Berg Balance Scale (BBS).
In the TUG test, the participants were instructed to get up from a chair, walk comfortably and safety for 10m, turn around, walk back to the chair and sit down. The chair had support for the arms and the participant could use it if necessary [31]. The time to perform the task was timed. When ≤10s, indicate great functionality, while >30s indicate significant impairment of mobility [32].
Each participant performed three tests. We selected the mean duration of the three tests for further analysis.
The BBS evaluate balance in 14 activities of daily living. For each activity, a score of 0 to 4 was given according to the performance (i.e., 0, unable to perform and 4, the best performance) [33]. We selected the final score BBS for analysis.
We evaluated postural balance using the kinetic displacement of the center of pressure (COP) on a force platform [34,35]. The frequency of data acquisition was recorded at 100Hz and filtered using a low-pass cut-off of 0.5Hz.

Statistical analysis
The statistical analysis was performed using SPSS, version 23 (SPSS Inc., Chicago, IL, EUA) and the level of statistical significance was set at 5%.
Correlations between the continuous variables were evaluated by the Pearson or Spearman coefficients. Association between PA and SB variables and postural balance and FOF outcomes were also assessed through multiple linear regressions adjusted for age, sex, BMI, and cardiovascular risk. The main predictors were defined after bivariate analysis, i.e., mean duration of the sedentary bouts, mean duration of the sedentary breaks and MVPA.

Results
The sample was mainly composed by overweight subjects with great physical fitness and postural balance ( Table 1).
The body sway and the COP area increased as the level of difficulty of the tests (i.e., eyes open to eyes closed and BS to ST stance) ( Table 1).
Although physically active, the participants spent 19 to 50 minutes in sedentary bout and nearly 60 hours per week in SB (Table 1).
We observed significant moderate correlations only between ST stance with eyes closed variables and PA and SB, especially with average amplitude. The TUG test time did not correlate to SB or PA ( Table 2).
The sedentary breaks play a more important role than the sedentary bouts and the PA in both static and dynamic postural balance outcomes, as well as the FOF (Table 3).

Discussion
We investigated the association between SB pattern, postural balance and the FOF in middle-aged and older asymptomatic adults. We observed that SB The SB is associated with health outcomes, regardless MVPA in older adults [15]. We found that the sedentary breaks were more important than the sedentary bouts and the PA for the static and dynamic postural balance and the FOF. Our results reinforce that encouraging breaking up sedentary time significantly improved physical function, as previously described [36]. We attributed our results to previous findings that relate sedentary breaks with better physical fitness and lower fragility [12,37]. Additionally, long sedentary bouts were associated with great deficits in activity daily living achievements, while the opposite was observed by increasing the number of sedentary breaks [38]. The frequency of breaking up SB is indirectly associated with low risk of deficits in the performance of activity daily living and physical dependence [37]. Subjects with great dependence on activity daily living have a high prevalence of fragility, which may justify such association with sedentary breaks.
The increased sedentary breaks and PA had a negative correlation with the FOF. Thus, our study reinforces that engaging in sports at least once a week was associated with lower levels of FOF [39]. Furthermore, we attributed our results to those reported by Rosenberg et al. [15] who found that sedentary time is associated with a greater FOF and worse physical function. Additionally, the FOF is strongly associated with postural instability in the elderly [4]. When they feel at risk of falling, the older adults tends to decrease the level of PA and, hence, the exposure to falls [6]. FOF is not independently associated with PA [40]. Our results do not agree with [40] since MVPA showed a negative correlation with FOF. Similar finding was observed in a previous study [14] 9 that concluded that FOF is an important barrier for older adults who want to benefit from walking and MVPA. This can be explained due to FOF is associated with changes in balance, mobility and muscle weakness [41], which can result in loss of physical abilities, poor quality of life, falls, frailty and mortality [42].
In our study, the sedentary breaks and PA had a negative correlation with the average amplitude in ML direction, suggesting a lower body sway. The sedentary bouts, however, result to great body sway. We attributed these results to the fact that SB have an association with physical performance [13] and causes a decrease in muscle strength, which is often reported among the older adults and may interfere with maintenance of postural balance [41].
SB pattern did not correlate with dynamic postural balance in the present study.
However, our sample was mainly composed by middle-aged adults, who are physically active e present great physical fitness. These sample characteristics may explain our less expressive results since aging leads to biomechanical limitations, worse postural balance, more time spent in SB and less sedentary breaks [2,10,43].

Conclusion
The SB pattern present a determinant association with postural balance and FOF in middle-aged and older adults. Additionally, our findings reinforce the importance of these subjects to perform the recommended amount of MVPA to maintain postural balance and reduce FOF.

Limitations of the study
Among the limitations, we addressed the study design. However, the use of triaxial accelerometer must be considered as a strength that allowed an objective measure of PA, SB and its pattern. Static and dynamic postural balance assessment were performed improving the generalizability of our data.

Ethics approval and consent to participate
The EPIMOV Study was approved by the local Research Ethics of Federal University of São Paulo (# 186.796). All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. All procedures were explained to the participants and they signed a free and informed consent form.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Consent for publication
Not applicable.