Revista Adolescência e Saúde

Revista Oficial do Núcleo de Estudos da Saúde do Adolescente / UERJ

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ISSN: 2177-5281 (Online)

Vol. 16 nº 1 - Jan/Mar - 2019

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Páginas 69 a 76

Influence of body mass index and level of physical activity on respiratory muscle strength and lung function of adolescents

Influencia del índice de masa corporal y nivel de actividad física en la fuerza muscular respiratoria y función pulmonar de adolescentes

Influência do índice de massa corporal e nível de atividade física na força muscular respiratória e função pulmonar de adolescentes

Autores: Viviane Soares1; Péricles Soares Bernardes2; Felipe Carlos Santos Batista3; João Martins de Oliveira Filho4; Daniella Alves Vento5; Patrícia Espindola Mota Venâncio6

1. Physiotherapist. Doctor in Health Sciences from the Federal University of Goiás (UFG). Goiânia, GO, Brazil. Professor at the University Center of Anapolis-UniEvangelica. Anápolis, GO, Brazil
2. Professor of Physical Education at Sesi-Jundiaí College. Anápolis, GO, Brazil
3. Student of the Course of Physical Education by the University Center of Anápolis-UniEvangelica. Anápolis, GO, Brazil
4. Student of the Physical Therapy Course at the University Center of Anapolis-UniEvangelica. Anápolis, GO, Brazil
5. Physiotherapist. Doctor in Health Sciences from the Department of Surgery and Anatomy of the Medical School of Ribeirão Preto, University of São Paulo - USP. Adjunct Professor of the University Center of Anapolis-UniEvangelica. Anápolis, GO, Brazil. Professor at the State University of Goiás (UEG). Goiânia, GO, Brazil
6. Doctor in Physical Education from the Catholic University of Brasilia. Professor of the University Center of Anapolis-UniEvangelica in the Didactics disciplines, psychomotricity, dance, gymnastics of the academy. Anápolis, GO, Brazil

Viviane Soares
Rua Amazonas, nº 294, Centro
Anápolis, Goiás. CEP: 75024-080

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Keywords: Adolescent; Obesity; Respiratory Muscles; Vital Capacity; Forced Expiratory Volume.
Palabra Clave: Adolescente; Obesidad; Músculos Respiratorios; Capacidad Vital; Volumen Expiratorio Forzado.
Descritores: Adolescente; Obesidade; Músculos Respiratórios; Capacidade Vital; Volume Expiratório Forçado.

OBJECTIVE: Evaluate the respiratory function and verify if the BMI and the NAF influence the muscle strength and the pulmonary function of adolescents.
METHODS: A cross-sectional study with a sample of 123 adolescents aged 13-18 years. Adolescents were classified into two groups according to BMI. The BMI was calculated and variables measured were: waist circumference, bioimpedance parameters (resistance, reactance and phase angle), fat free mass and body fat. The physical activity level (PAL) was estimated by specific instrument, respiratory muscle strength (maximum inspiratory pressure-´MIP and maximum expiratory-MEP) by manovacuometry and pulmonary function by spirometry (forced vital capacity-FVC, forced expiratory volume in the first second-FEV1 and FEV1/FVC).
RESULTS: The prevalence of overweight was 26.8%. PAL had no significant difference between groups (p = 0.69). Pimax (p = 0.007) and FVC (p = 0.005) were higher in overweight adolescents and the FEV1/FVC ratio was lower (p = 0.001). Multiple regression showed that BMI and NAF, adjusted for gender, age and sexual maturity were predictors of Pimax, explaining the relationship in 30% and FEV1/FVC in 9%. The BMI was a predictor of FEV1 (R2 adjusted=48%, p=0.001), FVC (R2 adjusted = 51%).
CONCLUSION: Overweight adolescents presented higher Pimax and FVC, while FEV1/FVC ratio was lower. It is believed that PAL and BMI directly influence respiratory muscle strength and lung function in adolescents.

OBJETIVO: Evaluar la función respiratoria y verificar si el índice de masa corporal (IMC) y el nivel de actividad física (NAF) influencian la fuerza muscular y la función pulmonar de adolescentes.
MÉTODOS: Estudio transversal con 123 adolescentes con franja etaria entre 13-18 años. Los adolescentes fueron clasificados en dos grupos de acuerdo con el IMC. El IMC fue calculado y las variables mensuradas fueron: circunferencia de cintura, parámetros de bioimpedancia, masa libre de grasa y grasa corporal. El NAF fue estimado por instrumento específico, la fuerza muscular respiratoria (presión inspiratoria máxima-Pimax y expiratoria máxima-Pemax) por la manovacuometría y la función pulmonar por la espirometría (capacidad vital forzada-CVF, volumen expiratorio forzado en el primer segundo-VEF1 y VEF1/CVF).
RESULTADOS: La prevalencia de exceso de peso fue de 26,8%. El NAF no tuvo diferencia significativa entre los grupos (p=0,69). La Pimax (p=0,007) y la CVF (p=0,005) fueron mayores en los adolescentes con exceso de peso y la relación VEF1/CVF fue inferior (p=0,001). La regresión múltiple mostró que el IMC y el NAF ajustados por el sexo, edad y madurez sexual fueron predictivos de Pimax, explicando la relación en 30% y de la VEF1/CVF en 9%. El IMC fue predictivo del VEF1 (R2 ajustado=48%, p=0,001), CVF (R2ajustado=51%).
CONCLUSIÓN: Los adolescentes con exceso de peso presentaron Pimax y CVF mayor y la relación VEF1/CVF fue menor. Se cree que el NAF y el IMC influencian directamente en la fuerza muscular respiratoria y función pulmonar en adolescentes.

OBJETIVO: Avaliar a função respiratória e verificar se o índice de massa corporal (IMC) e o nível de atividade física (NAF) influenciam a força muscular e a função pulmonar de adolescentes.
MÉTODOS: Estudo transversal com 123 adolescentes com faixa etária entre 13-18 anos. Os adolescentes foram classificados em dois grupos de acordo com o IMC. O IMC foi calculado e as variáveis mensuradas foram: circunferência de cintura, parâmetros de bioimpedância, massa livre de gordura e gordura corporal. O NAF foi estimado por instrumento específico, a força muscular respiratória (pressão inspiratória máxima-Pimáx e expiratória máxima-Pemáx) pela manovacuometria e a função pulmonar pela espirometria (capacidade vital forçada-CVF, volume expiratória forçado no primeiro segundo-VEF1 e VEF1/CVF).
RESULTADOS: A prevalência de excesso de peso foi de 26,8%. O NAF não teve diferença significativa entre os grupos (p=0,69). A Pimáx (p=0,007) e a CVF (p=0,005) foram maiores nos adolescentes com excesso de peso e a relação VEF1/CVF foi inferior (p=0,001). A regressão múltipla mostrou que o IMC e o NAF ajustados pelo sexo, idade e maturidade sexual foram preditores de Pimáx, explicando a relação em 30% e da VEF1/CVF em 9%. O IMC foi preditor do VEF1 (R2 ajustado=48%, p=0,001), CVF (R2ajustado=51%).
CONCLUSÃO: Os adolescentes com excesso de peso apresentaram Pimáx e CVF maior e a relação VEF1/CVF for menor. Acredita-se que o NAF e o IMC influenciam diretamente na força muscular respiratória e função pulmonar em adolescentes.


The global lifestyle has undergone gradual changes that endanger the health of children and adolescents and, in the future, the quality of life of adults and the elderly. Several factors contribute to this increased risk, but obesity is the trigger point for many imbalances in everyday life. Among them, we can highlight the inadequate food consumption with the substitution of lunch and dinner for unhealthy snacks unfavorable to health1. In addition, there is a low level of physical activity (NAF) and sedentary lifestyle, mainly due to the increase in Internet games and indiscriminate use of the cell phone that occupies the adolescent for hours without any stimulus to energy expenditure2,3.

The Study of Cardiovascular Risks in Adolescents (ERICA) traced the Brazilian adolescent profile and showed that in Brazil, the prevalence of obesity and physical inactivity (<300min/week) was 25.5% and 54.3%, respectively, with higher percentage in females3. These two conditions in the adult can induce structural changes, such as increased body and functional measures and perimeters, and specifically in respiratory function, may result in restriction of thoracic cavity mobility, increase in respiratory work, reduction of volumes and capacities, and reduction of tissue oxygenation4,5.

Obesity and low levels of physical activity in adolescents may not interfere with respiratory muscle strength and lung function6-8. Due to the fact that in this age group the adolescent manages to adapt to the mechanical conditions imposed on the excess weight and does not count on the consolidation of the ribs and reduction of the pulmonary complacency that occurs in the adult phase9. Based on this information, the objective of the present study was to evaluate respiratory function and to verify whether BMI and NAF influence muscle strength and lung function in obese and non-obese adolescents.


It is a cross-sectional study carried out in the middle school of SESI-Jundiaí College. Adolescents aged 13-18 years were recruited and excluded those with heart disease, acute asthmatic crisis and cognitive deficit, resulting in 123 students included in the research. The sample calculation was performed in GPower software, version 3.0 considering power of 80%, effect size of 0.5 and level of significance of <0.05. The research was approved by the Ethics and Research Committee of the University Center of Anapolis under No. 2,064,213/2017, following the guidelines of Resolution 466/12 of the National Health Council. All participants and managers received information about the study and signed the Term of Free and Informed Consent. The collections were in a reserved room on the premises of the college between January and March of 2018, always in the morning.

The level of physical activity was measured by a validated Self-Administered Physical Activity Checklist questionnaire for Brazilian adolescents10. The instrument contains a list of 24 moderate to vigorous physical activities (≥ 3METs) and white space for some activity that isn´t described. The data were filled in the classroom, containing the frequency (days/week) and duration (hours/min/day) of the activities. Adolescents with a practice of at least 300 min/week were considered active.

The body mass was collected with a digital scale (Filizola, model 2096 PP), where the adolescents remained with the minimum of possible clothing and stood upright and back to the balance display. The height was measured in meters (m) using the stadiometer (Sanny). For the accomplishment of this procedure the adolescents were in orthostatic position, feet barefoot and united. The BMI (body mass/squared stature) and its Z score were then calculated according to the World Health Organization11. After the calculation, the adolescents were divided into two groups, eutrophic and overweight/obese. Waist circumference was measured with a metal anthropometric tape (Sanny) with measuring point in the middle of the distance between the iliac crest and lower costal margin (12th rib).

The body composition was estimated by means of the electrical bioimpedance (BIA) with a tetrapolar apparatus (Quantum II, RJL system). The adolescents were placed in dorsal decubitus on a non-conductive surface and the limbs were spaced approximately 30º. They didn´t exercise eight hours before, didn´t consume alcohol in the 12 hours before the exam and didn´t pass any kind of lotion in the body on the day. The electrodes were positioned in the dorsal region of the hand (one between the ulna head and the radius and the other on the proximal phalanx of the third finger) and the foot (one electrode between the medial and lateral malleoli and another in the third metatarsal region). Three measurements of R (resistance) and Xc (reactance) were performed and the highest value measurement was used for analysis. The two bioelectrical measurements, R and Xc, in combination provided the phase angle (AF = tangent arc Xc/R)12. The values of fat free mass (MLG) and body fat (CG) were calculated by the following formulas13:

• MLG = 1.31 + (0.61 x height (cm) 2 /resistance) + 0.25 x body mass (kg)

• GC = body mass - MLG

Respiratory muscle strength was evaluated with a digital manovacuometer (MVD-300, Globalmed, Porto Alegre, Brazil). Maximal inspiratory pressure (Pimax) and maximal expiratory pressure (Pemax) were obtained from residual volume (RV) and total lung capacity (CPT), respectively14. The examination was performed with the teenager sitting, using a nasal fastener. Inspiratory and expiratory efforts were sustained for 1 second (s). The predicted values were calculated according to Domènech-clar et al.15.

Spirometry was performed using a portable device (Micro Quark, Cosmed) and specific disposable mouthpieces for adolescents aged 12-18 years. The criteria of acceptability and reproducibility were those recommended by American Thoracic Society/European Respiratory Society16. Measurements were forced expiratory volume in the first second (FEV1), forced vital capacity (FVC) and FEV1/FVC ratio. The classification of the disorders was performed using the lower limit of 70% of predicted.

Data were expressed as mean, standard deviation, frequency and percentages. The Student t-test or Mann-Whitney test were used to compare the groups according to the normality of the data. Multiple regression analysis, stepwise method, was used to evaluate the NAF and BMI as predictors of respiratory muscle strength and lung function. The models were adjusted for sex, age and sexual maturity. The value considered for p was <0.05. Data were analyzed in Statistical Package Social Science (SPSS).


The study had a total sample of 123 adolescents, being 55.3% male with ages between 14 and 18 years. The prevalence of overweight/obesity was found in 26.8% of adolescents. The NAF didn´t have a significant difference between the groups (p = 0.69) and, of the eutrophic and overweight adolescents, 19 (57.6%) and 59 (65.6%) were active, respectively. Pimáx (p = 0.007) and FVC (p = 0.005) were higher in overweight adolescents, while FEV1/FVC ratio was lower (p = 0.001) (Table 1). The phase angle was the only parameter that presented no significant difference (p = 0.26).

Figure 1 represents the comparison of maximum respiratory pressures between overweight and eutrophic adolescents. Pimax, which represents inspiratory muscle strength, was 16.3% higher in overweight adolescents. Only four adolescents from the overweight group had Pimax as expected. None of the evaluated patients had Pemax within the expected for age.

Figure 1. Comparison of maximal respiratory pressures among overweight and eutrophic adolescents.

Figure 2 shows the parameters of spirometry. When compared to the groups, pulmonary function had an FVC of 11.6% higher in overweight adolescents, while the ratio was 5.5% lower. Two eutrophic adolescents and one with overweight presented mixed ventilatory disorder.

Figure 2. Parameters of the spirometry of the adolescents analyzed.

The NAF and BMI were tested in multiple regressions as predictors of respiratory muscle strength and lung function (Table 2). The two parameters together, adjusted for gender, age and sexual maturity were predictors of Pimax, explaining the relationship in 30% and the FEV1/FVC ratio was explained in 9%. The BMI was a predictor of FEV 1 (R2 adjusted = 48%, p = 0.001), FVC (R 2 adjusted = 51%, p <0.001), while NAF predicted Pemáx (R2 = 41%, p = 0.02) and % FEV1 (R2 = 10%, p = 0.008).


The present study showed that overweight adolescents presented higher Pimax and FVC when compared to the eutrophic ones, while the FEV1/FVC ratio was lower. The majority of adolescents had lower than expected respiratory muscle strength. Regarding pulmonary function, only two eutrophic adolescents and one with overweight had mixed ventilatory disorder. NAF and BMI were direct predictors of respiratory muscle strength and lung function, and BMI was an inverse predictor of FEV1/FVC ratio.

Pimax was higher in overweight adolescents. This result was also shown in a study comparing eutrophic and overweight 6. However, there is evidence that Pimax is similar in both groups8,17. The higher Pimax in adolescents with excess weight can be explained by biomechanical and physiological factors in which the distribution of body fat in the abdominal region would be the main mechanical factor9. However, in the present study, even with obese individuals presenting higher CC, the majority presented the measures within the predicted for age and sex. It is worth mentioning that in this age group, the reduction of complacency and the consolidation of the ribs still do not influence the respiratory mechanics9.

Regarding the evaluation of pulmonary function, this is fundamental to detect the changes in the conduction of VAs and the restrictive barrier imposed by obesity. The FVC was higher, while the FEV1/FVC ratio was lower in obese adolescents. There are similar results in the literature, in which overweight Thai children and adolescents tend to have a lower FEV1/FVC ratio, which is compatible with VA obstruction17. No differences in lung function were found in Canadian adolescents with and without excess weight7. Even though the obese adolescents in this study had a higher FVC and a lower FEV1/FVC ratio, only three adolescents were diagnosed with a mixed ventilatory disorder (two eutrophic and one with overweight), showing that changes in lung volumes occur only in people with extreme BMI (> 45 kg/m2), but remain with partial pressure of normal oxygen18.

The level of physical activity evaluated in min/week didn´t present a significant difference among adolescents, a fact also observed in another study with children/adolescents8. However, when the level of physical activity was used as a predictor of respiratory function along with BMI, it had influence on respiratory muscle strength, FEV1 and FEV1/FVC ratio. BMI is the most used parameter to evaluate overweight and is considered a general health marker, presenting a positive relation with Pimax, FVC and FEV1 and negative relation with FEV1/FVC ratio. These findings contribute to the studies found in the literature7,8,19 that stress that at this stage of life the body can adapt to the condition of being overweight. However, with the advancing age it is known that this relationship (overweight and respiratory function) becomes inversely proportional and special attention is needed to food consumption and physical activity as strategies to prevent future problems.

The strengths of this study are related to the study of the respiratory function of adolescents, since the number of studies involving this population and the condition of excess weight is reduced in the literature. Adolescents diagnosed with asthma were excluded, which made it possible to avoid a selection bias because this clinical condition already presents, to a greater or lesser degree, airway obstruction. Another point to be highlighted was the possibility of verifying the influence of BMI and NAF on respiratory muscle strength and lung function. It is important to emphasize that BMI is a general marker of obesity and it is possible that the distribution of body fat may influence respiratory function. Thus, other markers such as percentage of body fat and blood cholesterol dosages and their fractions can be used to fill this gap.


Based on the study, it was concluded that adolescents with excess weight had higher inspiratory power and FVC when compared to eutrophic, when FEV1/FVC ratio was lower. The majority of adolescents had respiratory muscle strength below predicted for age, body mass, and height. Regarding lung function, only two adolescents presented mixed ventilatory disorder. It is believed that NAF and BMI are directly related to respiratory muscle strength and lung function in adolescents and that BMI was a negative predictor of FEV1/FVC ratio.


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