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 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’O2), 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’O2 (ml/min/kg) during the last 15s was representative of the peak V’O2 (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].
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).
Anthropometric measures and body composition
We measured height (m) and body mass (kg) by using a digital balance with a stadiometer (Toledo®, São Paulo, Brazil). Then, we calculated BMI (Kg/m2). We assessed body composition trough tetrapolar bioelectrical impedance (310eBIODYNAMICS, Detroit, EUA), as previously described [26, 27]. 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 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. Participants were evaluated with arms held alongside the body in bipedal stance (BS) and in semi-tandem stance (ST) for 30s in each test with eyes open (fixating a point at 1m in front of them) andwith eyes closed. Participants performed one trial for each condition. Body sway was measured along anteroposterior (AP) and medial-lateral (ML) directions. We recorded average amplitude, median frequency, and COP area for further analysis.
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.