The ageing of the population has become a reality in most of the world in recent decades. Changes in the living conditions and advances in medicine, reduced early mortality and promoted the increase in life expectancy [1]. The number of elders in Brazil is growing rapidly according to data from the Brazilian Institute of Geography and Statistics (IBGE), which estimates that by 2025 this population will have reached 32 million, placing Brazil as sixth in the world in the number of elderly people [1 , 2].

As the population increases, the incidence of pathologies grows proportionally, and respiratory diseases are among the most important causes of death [3 , 4].

With the aging process, there is a reduction in skeletal muscle strength and in respiratory muscle strength, resulting in a functional decline and decreasing performance in activities of daily living (ADL) [5].

Preventive physical exercise should be stimulated aiming at maintaining the independence of the elderly, increasing their functional performance, and providing the preservation or recovery of the organic functions affected by the aging process, preventing several pathologies [3].

Respiratory physical training provides results such as an increased ability of the inspiratory muscles to generate force and greater sustainment of a given inspiratory pressure level and may reduce sensations of respiratory effort [3].

The POWERbreathe K-series trains the inspiratory muscles using a resistance, with the possibility of automatically adjusting its load to follow the evolution of the individual [6]. Functional training originated from rehabilitation when movements were used to recover from injuries and postural changes [7].

Thus, the study aimed to assess the effects of respiratory training associated with functional training on respiratory muscle strength, lung function, and functionality of the elderly.

All data collected in this study were analyzed using the Statistical Package for the Social Sciences ver. 7.0 (SPSS Inc., Chicago, IL, USA). We evaluated the variables of age, gender, weight, height, and BMI of all individuals. A one-way ANOVA analysis was conducted to compare the values of the quantitative variables between the experimental groups. For the gender variable, we carried out the Chi-square test for independence.

A Shapiro-Wilk Test for the assumptions of normality of residuals, and Cochran’s Test for homogeneity of variances. Subsequently, we employed the mixed model of Factorial Analysis of Variance for Repeated Measurements, then the LSD-Fisher follow-up test. We used the data referring to Gender, Age, Weight, Height, and BMI tabulated as descriptive statistics subdivided into groups undergoing respiratory training and respiratory + functional training. The gender variable was compared between the groups employing the Chi-square test for independence and the other variables were compared using the t-Test. The level of statistical significance was set at p < 0.05 [12 , 13].

Observing the physical variables of the sample with 27 individuals evaluated pre and post-intervention we found no significant differences regarding age, weight, height, and BMI among the groups (p > 0.05), with homogeneity of the individuals distributed among the groups (Table 2).

The statistical analysis evidences a significant difference in the respiratory group. MaxIP is considered the highest pressure generated during an inspiration, forced against an occluded airway [14 , 15]. With age, there is a reduction of the diaphragmatic and accessory muscle mass associated with a decline in the production of respiratory work for the same level of neural stimulus, remodeling of motor units, and a

decrease in the levels of protein synthesis [15 , 16].

Esteves et al. (2016) [17], when reporting the effects of inspiratory muscle training in healthy individuals who used the Power breathe device, observed an increase in MaxIP, and considered that this gain is due to neural changes that occurred in the inspiratory muscles, that these neural adaptations result in better recruitment of motor units, and in the speed at which the motor neurons are triggered. Furthermore, they state that these neural changes would only occur after five or six weeks of training, and muscle hypertrophy is not possible before eight weeks. This finding emphasizes our training protocol, carried out in 12 weeks, generating an increase in inspiratory muscle strength.

Souza (2014) [18] reports a different justification for the increase in MaxIP, citing that the increase in mechanical activity in the inspiratory musculature provides greater thoracoabdominal mobility, and stimulates the mechanical reorganization of all respiratory muscles, enhancing the variable measured.

For the MaxEP variable, we did not notice significant improvements in the groups. Vasconcelos et al. (2007) [19] carried out a study to verify the correlation between the strength of respiratory muscles through the maximum inspiratory pressure (MaxIP) and maximum expiratory pressure (MaxEP) and functional capacity by the 6 MWT. The results obtained were like our study where the values of the Pearson Correlation coefficients between the distance walked and the MaxIP and MaxEP were, respectively: r = 0.44 (p = 0.005) and r = 0.27 (p = 0.11). There was a positive correlation only for MaxIP, recommending the RMT for physical rehabilitation programs, aiming at improving functional capacity in the elderly.

These results may be due to the structure of the flattened mouthpiece used in both studies. With this mouthpiece, it is possible to observe a discrete air leak around it, even in healthy individuals who present adequate labial pressure.

Considering the SF-36 quality of life test, we did not observe significant differences in all its domains. Compolina et al. (2009) [20] assessing the impact of chronic disease on the quality of life of the elderly, concluded that in general, the lowest averages are found for limitations due to physical aspects, while the highest for limitations related to social and psychological aspects. However, the participants of our study performed their activities of daily living with excellence and did not present any depressive symptoms, discouragement, or complaints arising from chronic diseases, explaining our result. These findings demonstrate that aging may not be the main factor for the decrease in quality of life, but rather, social isolation and poor physical and mental activity.

In the Sit to Stand Test, there was no statistical difference between the groups, however, in all groups, there was a significant reduction in the performance time. The objective of the test is to quantify the muscular strength of the lower limbs through repeated performances [21]. Muscular weakening, characterized by Type II muscle fiber atrophy, results in a functional disability, whereas the strength of lower limbs can be used as a predictor of functional disability in the elderly [22]. Rabelo and Oliveira (2004) [23] argued that regular physical activity may delay declines associated with aging, in the processing speed of the central nervous system, enhancing its reaction speed, and may effectively contribute to its functional capacity.

Weiner et al. (2003) [24] observed an effective gain using the 6 MWT, concluding that the increase of respiratory muscle strength provides a reduction of dyspnea in maximal exercises, inducing a functional improvement. This explains the improvement of the individuals in our study who participated only in respiratory muscle training (RMT).

The 6 MWT showed no significant increase. We observed a tendency of elevation in the values of the test after the intervention procedures. With the physiological process of aging, the maximum force exerted (peak torque) decreases. The peak torque represents the point of highest torque (muscle strength) in the range of motion, that is, the value corresponding to the maximum functional muscle strength associating power to the highest speed. Felicio et al. (2015) [25] evaluated muscle function using the isokinetic dynamometer at angular velocities of elderly women to compare performance between different age groups. They observed that the elderly with a greater age range presented worse results in the variables when compared to the younger ones, confirming that with age there is a greater tendency towards a decrease in muscular function, even amongst active individuals.

Studies with similar anthropometric characteristics demonstrate that the variables sex, weight, height, and age influence the evaluation of distance [26 , 27].

The spirometric variables FVC (forced vital capacity) and FVC1/FVC (Tiffeneau index), had a significant difference in the group with the interaction of the factors (Respiratory Training + Functional Training) (p = 0.01), between the moments pre and post-intervention.

Comparing each variable, we confirmed that air trapping is a characteristic of the elderly. This is aggravated even more by physical inactivity or the absence of respiratory muscle training [28].

Medical literature states that nothing can be looked at separately in the elderly. The aging process is a set of signs and symptoms or even biological, physiological, anatomical, and/or structural alterations. An individualized look at variables is not always coherent [22].

The study of FEV1/FVC showed a favorable result [29]. More air volume was exhaled, and vital capacity increased, consequently improving pulmonary ventilation [30]. This suggests that this is also likely to interfere with greater CO₂ elimination and improved elastic recoil [31]. Gas exchange with a greater possibility of effectiveness and improved expansibility of the bone and cartilaginous structure can be explored. More toned muscles effectively collaborate to achieve that [28 , 32].

The FEV1/FVC ratio is indeed the most relevant variable according to the guidelines, which prescribe it and indicate spirometry for that purpose [29 , 33]. Spirometry is still the main respiratory functional tool and is expected to remain so for decades. It is considered a test of easy applicability and high reproducibility [34].

Important aspects may be improved with this variable and may help in the longevity of the world population affected by respiratory complications. Longer time between exacerbations and a reduction in the number and frequency of hospitalizations [30 , 35].

The significant results of this variable further enhance the results obtained, strengthen the theory, and corroborate the studies that show that the elderly need treatment and training together, from the functional aspect to the muscular.

Regular exercise provides a normalization of the relationship between tension and the length of muscles, an increase in blood supply, and an improvement of cellular metabolism [36]. Associated with RMT, it guarantees thoracic mechanical adequacy, decreasing the ventilatory necessity for submaximal exercises by increasing the oxidative capacity of muscle fibers, thus decreasing the senile restriction found in the elderly.

Professionals working with the elderly need to have a different look at the training of the respiratory muscles in a resisted manner, which sometimes is neglected. This fact can be verified in a meta-analysis published in 2020, global muscle training, without the use of respiratory muscle strengthening [37].

No study with this scope and methodology has managed to significantly alter this important spirometric data in the last 10 years with the use of the descriptors (((respiratory muscle resistance training) AND (elderly)) AND (lung function)) AND (spirometry) [38].

Annual spirometry is recommended to assess the natural response of the functional decline, as well as the response to the changes that will occur with the decision to replicate this model of treatment and others to which this proposal may contribute [34].

Studies comparing volumes and pulmonary capacities have stated that the vital capacity decreases while the residual volume increases. However, the total lung capacity presents few changes. These physiological changes, such as a decrease in pulmonary ventilation, reduction in the elasticity of the alveoli, subtraction of vital capacity, and thoracic rigidity and calcification of the ribs justify the non-significance in the spirometric variables [18 , 22 , 39].

PEF did not show any significant difference; however, all groups showed an increase in the means after the intervention. According to Fonseca et al. (2010) [40], the PEF is considered an indirect indicator of obstruction of the large airways and is affected by the degree of lung insufflation, thoracic elasticity, abdominal muscles, and muscle strength of the patient. With aging, there is a decrease in thoracic mobility due to the decrease in mobility of the costovertebral joints, the intervertebral disc becomes flat, resulting in a rigid thorax. The lung parenchyma, composed of elastic tissue (elastin), distends, and its hyperinflation generates a premature constriction in airways during expiration (point of equal pressure), favoring retention of air, and reducing the capacity of the elastic retraction of the lung. Both respiratory and functional training provided improvement in the strength and endurance of the respiratory muscles, improving thoracic-abdominal mobility and the capacity of physical exercise.

The functional training associated with respiratory training in the elderly population contributes to the gain of muscle strength and improvement of functional capacity, echoing the elderly functionality. It can also be concluded that physiotherapy, globally focused on the individual is of extreme importance for the elderly, allowing them to be independent in their everyday life activities.

The study had sample limitations, especially due to the dropout from the control group, hindering our criterion of efficiency of the training protocol. Another limitation was the inability of the participants to understand how to perform the breathing tests. We propose new studies with analysis of the variables studied for comparison with our results and validation of our methodology.

Coordination for the Improvement of Higher Education Personnel (CAPES) and National Council for Scientific and Technological Development (CNPq).

The authors declare no conflicts of interest regarding the publication of this paper.