Evaluations to characterize the elderly participants
Assessment of functional capacity
To assess functional capacity, the Glitter-ADL test [31] will be used at three points (pretraining, post-training and 30 days after the end of training). T's an instrument validated for patients with chronic obstructive pulmonary disease, with acceptable reliability (95% CI −0.20 to −0.54).
The Glittre-ADL test is an instrument validated for patients with chronic obstructive pulmonary disease, with acceptable reliability (95% CI −0.20 to −0.54) [
31], which has been previously tested in healthy older adults [
38,
39], showing excellent intra-rater (ICC 0.90, 95% CI 0.86–0.93) and inter-rater (ICC 0.91, 95% CI 0.88–0.94) reliability (
P < 0.001 for both). The intra-rater standard measurement error was 0.03 min and the inter-rater standard measurement error was 0.05 min. The minimal detectable change for intra-rater was 0.40 min and for inter-rater was 0.07 min.
The Glittre-ADL test consists of getting up from a chair with a backpack containing one weight (2.5 kg for women and 5.0 kg for men), walking 5 m on a flat track, going up and down steps measuring 17 cm in height and 27 cm in depth, and walking another 5 m to a set of three shelves, one at the top (at shoulder level), one in the middle (at pelvic waist level) and one at floor level. When reaching the shelves, the participant should transfer three balls, weighing 1 kg each, from the top to the middle and then to the bottom shelf and finally from the bottom shelf to the floor, and then return the balls in the same sequence until they reach the upper shelf. The task should be repeated in the reverse sequence until the participant is sitting again.
The complete test consists of five repetitions of this circuit, which should be performed as quickly as possible. Performance is given by the running time (in minutes) of the five laps with a shorter the time indicating better performance, considering a clinically important improvement between 7 and 40 s [
38]. To be considered as preserved functional capacity, the test must be performed in approximately 2 min [
39].
At the beginning and end of each repeat of the Glittre-ADL test, all of the following measures will be performed for safety monitoring only and will not be used for performance analysis of the Glittre-ADL test as described by Skumlien et al. [
31]: blood pressure (measured with a sphygmomanometer; Incoterm model 29,848), heart rate (measured using a Polar FT1 and FT2 monitor), oxygen saturation (measured with a portable digital oximeter) and dyspnea and lower extremity fatigue (using the dyspnea Borg test) [
28].
Assessment of walking ability
The ability to walk will be assessed by the 6MWT [
32], which will be performed at three time points (pre-training, post-training and 30 days after the end of training) in a flat corridor along a 30-m track with markings at each 405 meter.
Participants should walk as fast as possible, without running, while trying to maintain the same pace for 6 min. The participant will be given verbal encouragement every minute using standardized phrases such as “you’re doing well”, “keep up your work”, “you’re halfway there” and “you only have two minutes left” with no expressions or other signs to speed up the pace. If a participant becomes tired, they may slow down or even stop. In the latter case, the timer will not be stopped and the participant will be encouraged to resume the test as soon as they can until the full 6 min are completed.
The test is evaluated by the number of meters traveled during the 6 min, with more meters traveled indicating better test performance.
Heart rate and oxygen saturation will be measured at the third minute of the test. Heart rate, respiratory rate, blood pressure, oxygen saturation and Borg scales [
28] for shortness of breath and lower limb fatigue will be assessed at the beginning and end of the test. The 6MWT is a reliable measure that has been validated for the older adult population, with a test–retest reliability of 0.95 [
40].
Assessment of balance
We will use the mini-BESTest to assess balance [
33], which consists of four domains.
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Domain 1 (anticipatory postural adjustments) evaluates the participant’s ability to move from a sitting to standing position, stand on tiptoes, and stand on one foot (right then left).
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Domain 2 (reactive postural responses) evaluates the participant’s ability to perform a protection reaction (during instability) with a step forward, a protective reaction (during instability) with a backward step, and protection reaction (during instability) with a lateral step (right and left).
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Domain 3 (sensory orientation) evaluates the participant’s ability to stand with their eyes open on a firm surface with feet together, stand with their eyes closed on an unstable surface with feet together, and to stand on a ramp with their eyes closed.
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Domain 4 (gait stability) evaluates the participant’s ability to change gear while walking, to walk with head movements (rotate the head horizontally), to walk and turn on an axis, to overcome obstacles, and a timed up and go test associated with another task (double-task) by performing a countdown.
The score is given by the performance in the execution of each domain, and each sub-item of the domains is scored as follows: 2 points for normal performance; 1 point for moderate performance; and 0 points for poor performance. The score ranges from 0 to 32 points, with a balance deficit being defined as a score below 24 points.
The participants will perform the tests without shoes. If they are unable to perform any movement independently, minor adjustments or assistance may be made, but their score will be lower. Instructions for each test will be provided in advance so that the participants can perform each test to the best of their ability. Up to three attempts will be allowed and the best result will be considered for analysis. The mini-BESTest is a reliable measure that has been validated for the elderly population, with test–retest reliability (ICC) ranging from 0.50 to 0.82 [
33].
Assessment of functional independence
The FIM will be used to assess functional independence [
34] and will be administered to the participants in interview form to quantify the degree of assistance required during activities of daily living.
This measure has 18 categories grouped into six dimensions for the evaluation of functional and cognitive status: self-care (eating, grooming, bathing, dressing upper body, dressing lower body, toileting), sphincter control (bladder management, bowel management), transfers (bed/chair/wheelchair, toilet, bathtub/shower), locomotion (walk/wheelchair, stairs), communication (comprehension, expression) and social cognition (social interaction, problem solving, memory).
The value attributed to each item ranges from 1 to 7 and is interpreted as follows: 7, completely independent (activity is executed without assistance); 6, modified independence (activity requires special device, care and safety); 5, supervised (individual requires control, support from another person, but with no physical contact); 4, assistance with minimal contact (individual performs >75% of the task without assistance); 3, moderate assistance (individual performs >50% of the task without assistance); 2, maximum assistance (individual performs >25% of the task without assistance); 1, total assistance (individual performs less than 25% of the task without assistance).
The total is calculated from the sum of the FIM dimensions and ranges from 18 to 126 points. The total is divided into four subscores: 18 points, complete dependence; 19 to 60 points, modified dependence (assistance on up to 50% of the task); 61 to 103 points, modified independence (assistance on up to 25% of the task); 104 to 126 points, complete independence. The Brazilian version of the FIM has been validated [
34], with high test reliability (ICC = 0.91 to 0.98) and inter-observer reliability (ICC = 0.87 to 0.98).
Assessment of quality of life
We will use the WHO Quality of Life Instrument to assess quality of life [
35], which will be administered as an interview.
This instrument consists of 26 items divided into four domains: physical, psychological, social relations and environment. Each item will be rated with a score (from 1 to 5) awarded according to the domain being evaluated: very bad, dissatisfied, nothing or never (1 point); too little, bad, sometimes dissatisfied (2 points); medium, neither bad nor good, neither satisfied nor dissatisfied, more or less often (3 points); very, good, quite, good, satisfied and very often (4 points); completely, very good, very satisfied, extremely, completely, very good and always (5 points).
The score ranges from 26 to 130 points, with higher scores indicating a better quality of life.
Data analysis
To identify data normality and cases of non-normal distribution, data distribution analyses will be performed by visual analysis of the histograms of each treatment group. Descriptive statistics will be used as measures of central tendency and dispersion, mean and standard deviation will be used for quantitative variables, frequency will be used for categorical variables and the median and the interquartile range will be used for nonparametric variables.
An ANOVA of two factors followed by the Bonferroni test will be used for comparative analysis between groups (active and sham tDCS) along the time points (pre- and post-training).
A P value <0.05 will be considered indicative of statistical significance, and Pearson correlation will be used to calculate the relationship between Glittre-ADL performance and the secondary outcomes of the capacity to walk (6MWT), balance (mini-BESTest), FIM, instrumental activities of daily living, quality of life, and evaluation of muscle strength at pretraining, following treatment and at 30-day follow-up.
Individual results will be analyzed later for each outcome. These individual data will be an important complement to identifying the clinical relevance of the results [
42].
Clinical characteristics, especially outcome-related characteristics, and functional capacity (Glittre-ADL test) will be compared at baseline to ensure homogeneity of the groups. The significance level of P < 0.05 refers to the alpha risk adopted in the ANOVA test. If there is a significant difference between groups, times, or interactions between groups and time, the P value of the multiple comparison analysis from the Bonferroni post-hoc test will be adopted.
All analyses will be processed using the SPSS program (IBM SPSS Statistics for Windows, Version 22.0, released in 2013, IBM Corp., Armonk, NY, USA). In case of dropouts and missing data, an intention-to-treat analysis will be performed using the appropriate imputation method according to the missing standard, the data will be analyzed when participants receive no treatment (or are under a control condition) depending on the group assigned, and when outcome measures are available an analysis will be performed as if the individuals had received the treatment (or a control condition).