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Brazilian Journal of Physical Therapy

Print version ISSN 1413-3555

Rev. bras. fisioter. vol.14 no.6 São Carlos Nov./Dec. 2010 



Relationship between cough strength and functional level in elderly



Fábia S. FreitasI; Cássio C. IbiapinaII; Cristina G. AlvimII; Raquel R. BrittoIII; Verônica F. ParreiraIII

IPhysical Therapy Department, Pontifícia Universidade Católica de Minas Gerais (PUC Minas), Belo Horizonte (MG), Brazil
IIDepartment of Pediatrics, Faculty of Medicine, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte (MG), Brazil
IIIPhysical Therapy Department, School of Physical Education, Physical Therapy and Occupational Therapy, UFMG

Correspondence to




BACKGROUND: Respiratory muscle strength is influenced by aging.
OBJECTIVES: To assess, in a healthy elderly population, the influence of physical activity and functional performance on the pulmonary function parameters, on respiratory muscle strength and on coughing.
METHODS: Observation study that sixty one elderly with age equal or more than 60 years (72.3±7.2 years), with normal spirometry were included. Maximal Inspiratory Pressure (MIP), Maximal Expiratory Pressure (MEP), Peak Expiratory Flow (PEF), Peak Cough Flow (PCF) and Human Activity Profile (HAP) were evaluated. The elderly were separated in two groups (active and moderately active) according to HAP. Student's test was used for univariate analysis and regression analysis models was used for multivariate analysis.
RESULTS: Elderly participants who were classified as active presented on average 13.5 cmH2O higher MEP (88±21.4 cmH2O), and 16.2 cmH2O higher MIP (76±17.7 cmH2O). Maximal respiratory pressure decreases 1 cmH2O per year. The PEF and PCF were higher for male (p<0.001) and active elderly (p=0.046 e p=0.004 respectively). A positive correlation was observed between HAP and the following variables: MEP MIP and PCF (r=0.527, p<0.001; r=0.498, p<0.001 and r=0.365, p=0.004, respectively).
CONCLUSIONS: The active life style can positively affect the respiratory muscle strength and PCF values. Aging is associated to respiratory muscle strength reduction (both inspiratory and expiratory). Women showed lower PEmax.

Key words: aging; physiopathology; cough; muscle strength; physiology; elderly.




The aging process promotes a series of organism modifications, especially changes in the respiratory system1 such as the reduction of the total lung capacity (TLC), the forced expiratory volume in one second (FEV1) and the forced expiratory flow (FEF), as well as increases the functional residual capacity (FRC) and the expiratory reserve volume (ERV). These changes are related to decrease both lung elastic recoil and the thoracic complacency capacity2,3. Such alterations when associated with a reduction of muscle strength can lead to a reduced peak expiratory flow (PEF)2,4. On the other hand, Britto et al.5 have found no significant differences in relation to the variables volume and timing of the breathing pattern when comparing adults with elderly.

In the musculoskeletal system, there is a reduction in respiratory muscle strength with the aging process3,6-8. Tolep et al.9 observed a reduction of up to 25% of the diaphragm strength in elderly compared to young adults. Moreover, Caskey et al.10 found a higher prevalence of diaphragm alterations in the elderly when assessing 120 chest and abdominal computed tomography scans.

Tolep et al.11 described that there is skeletal muscle atrophy with aging, which affects mostly type II fibers (fast twitch fibers). Several factors are associated with this statement, such as a reduction of physical activity, alterations of neuromuscular function, nutritional state and hormonal factors12. The reduction of the respiratory muscle strength may affect its ventilatory and non-ventilatory functions, being the latter related to coughing, speeching and swallowing13.

Cough is an important defense mechanism of the bronchial tree14-16 that relies on the capacity to generate flow and speed in the airway17 and it is directly related to respiratory muscle strength18. The muscle weakness and the alterations in the pulmonary parenchyma that are observed in the aging process can affect the ability to generate a satisfactory airflow for coughing, decreasing its efficacy and increasing the risk of developing acute respiratory tract infection. According to Salam et al.18, peak cough flow (PCF) is the most reliable way to evaluate cough strength and recently it has been used frequently to assess patients with neuromuscular diseases. Smina et al.19, observed that cough strength is a strong predictor of successful extubation outcome of patients without neuromuscular diseases, being also a good predictor of hospital mortality.

McConnell and Copestake4 in 1999 and more recently Watsford et al.8 attempted to determine the influence of physical activity on respiratory muscle strength and they found that physical activity has an important role for maintaining both inspiratory and expiratory muscle strength. Therefore, regular physical activity could indirectly improve the airway defense mechanisms since gaining strength could contribute to increase the effectiveness of cough.

The assessment of respiratory muscle strength measured by maximal respiratory pressures is an important tool in the daily routine of the respiratory physical therapist. The cough strength evaluation has been poorer explored in the assessment of patients. Therefore, the objective of this study was to assess the influence of physical activity and functional level on pulmonary function parameters, respiratory muscle strength and cough in a sample of healthy elderly.




The study sample consisted of 61 elderly (14 males and 47 females) aged equal to or greater than 60 years (mean age = 72±7.2 years) who were recruited in community centers. This study was approved by the Research Ethics Committe of the Instituto de Previdência dos Servidores do Estado de Minas Gerais (IPSEMG)/Hospital Governador Israel Pinheiro, Belo Horizonte (MG), Brazil (CEP 257/07), and all participants gave written informed consent.

The inclusion criterion was age equal to or greater than 60 years. The exclusion criteria were: recent thoracic or abdominal surgery; thoracic pain of surgical origin; pulmonary disease reported by the participant and/or obstructive, restrictive or mixed ventilatory disturbance observed by spirometry; neurological diseases that would undermine the accomplishment of the tests, and difficulty to understand and/or to perform the tests.

Study protocol

Subjects initially responded to a questionnaire adapted from the American Thoracic Society (ATS)20 to evaluate the presence of chronic obstructive pulmonary disease (COPD), asthma or other pulmonary diseases, and those without pulmonary symptoms performed spirometry. Later, the participants responded the Human Activity Profile (HAP) that is a questionnaire used to assess the level of physical activity21, and performed tests for respiratory muscle strength, peak expiratory flow (PEF) and peak cough flow (PCF). A minimum rest time of one minute was given between the tests, being the rest longer if needed by the participants.


  • Spirometry: The protocol to perform the test followed the 2002 Guidelines for Pulmonary Function Tests2. The SBG- SDI Diagnostics Spirometer (Easton, Missouri-USA) was the selected instrument.

  • Assessment of regular physical activity: According to the Brazilian Society of Cardiology, subjects who informed that they performed physical activity (i.e. swimming, walking, jogging, aerobics, cycling) for at least 30 minutes three times a week were classified as "physically active (PA)", and those who performed physical activity with a lower duration and frequency were classified as "physically inactive" (PI)23.

  • Assessment of functional level: Functional level was assessed using the HAP questionnaire, which is recommended to evaluate the level of functional ability in both healthy individuals and those with some degree of impairment, at any age group. This questionnaire was translated and validated for the Brazilian population in a study that evaluated 230 functionally independent elderly24. The HAP investigates the ability to perform routine activities, ranging from low to high functional level. The adjusted activity score (AAS) can be used in a qualitative way, by classifying the individual as inactive (AAS<53), moderately active (AAS 53 –74) and active (AAS>74)24.

  • Assessment of respiratory muscle strength: The measurement of the maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) were used to assess the inspiratory and expiratory muscle strength respectively. The measurements were obtained through a portable manometer device (Wika - São Paulo, SP, Brazil), with operating range from -300 to +300 cmH2O.

The MIP was performed from the residual volume, and the MEP was performed from the total lung capacity. Participants were in a sitting position with feet supported, using a nose clip and exerting pressure on the lips to prevent air leakage around the mouthpiece. They were instructed to breathe through the mouthpiece, inhaling (MIP) or exhaling (MEP) with as much effort and as fast as possible for at least one second. They performed each measure at least five times until three acceptable and reproducible ones were obtained, that is, with no leakage and with a difference between the measures of less than 10%25. All measures were taken by the same examiner.

  • Assessment of peak expiratory flow and peak cough flow: The Mini-Wright Peak Expiratory Flow Meter (Clement Clarke, Harlow, England), with a scale ranging from zero to 900 L/min, was used for these measurements.

Subjects performed at least three measures that, when necessary, were repeated until three values with a maximum difference between them of 20 L/min were obtained22. The highest value was recorded. The PEF was obtained from a maximal inspiration followed by a rapid and vigorous exhalation, which could not be accompanied by coughing or exhalation prolonged for more than two seconds22. The PCF was obtained from a maximum inspiration followed by the most vigorous cough possible for the subject26.

Statistical analysis

The Student's t test was used to compare the outcome variables and the categorical covariates, which met the criteria for normality and homocedasticity. The Pearson Correlation Coefficient (r) was calculated to compare the outcome variables with the quantitative covariates27. The level of significance adopted for the analysis was of 5%.

The AAS variable was analyzed using both quantitative and qualitative methods. Linear regression models were developed for each quantitative outcome variables of the study. Initially, all variables that presented at least a trend for statistical significance (p<0.25) in the univariate analysis was included in the multivariate model. Then, the variables were excluded from the model by stepwise elimination until the final model presented only the variables that achieved statistical significance (p<0.05), but also considering their clinical relevance. Further, all interactions between variables that were present in the final regression model were tested. Only the models that had at least one of the variables at a significance level of 5% were adjusted.



Eighty-seven elderly were included in the study. According to the inclusion criterion, those who were aged 60 years or older were selected for the study. According to the exclusion criteria, 26 subjects were excluded (16 for presenting changes in the pulmonary function on spirometry, eight for being unable to understand and/or to perform the pulmonary function test and two for presenting thoracic pain during the tests). Therefore, 61 elderly were assessed (30 active and 31 moderately active). Among them, 35 subjects were classified as PA and 26 as PI. A total of 88.5% of participants reported that have never smoked and 7% were former smokers. Only one subject was illiterate, 31% had complete elementary education, 39% were high school graduates and 11.5% had a university degree.

Table 1 shows data related to age, body mass index (BMI) and FVC, FEV1, FEF25-75% values for the final sample of 61 elderly.



Maximum expiratory pressure and maximum inspiratory pressure

Table 2 shows the comparisons between MEP and MIP mean values and the variables gender, AAS and physical activity. In relation to MEP, there was a significant difference between men and women (90.0 and 74.9 cmH2O respectively, p=0.001), being men having a higher MEP than women. Subjects who were considered active by the AAS also showed higher MEP (p=0.025). For MIP, the only statistically significant difference was that the active subjects showed higher MIP than the moderately active ones (p<0.001). Regarding the reporting of participants on whether they were physically active or not, no significantly between-group difference was found for MEP or MIP (p=0.175 and p=0.990, respectively).

A moderate and positive correlation was observed between MEP and quantitative AAS (r=0.527, p<0.001). A weak and negative correlation was found between MIP and age (r=-0.359, p=0.005), and the correlation found between MIP and AAS was moderate and positive (r=0.498, p<0.001).

Table 3 shows data related to the regression analysis that demonstrated that MEP is, on average, 17.2 cmH2O higher in men than in women, and 13.5 cmH2O higher in participants who were classified as active by the AAS. MIP was on average 16.2 cmH2O higher in active participants. The regression coefficients found for age were -1 and -0,8 for MEP and MIP, respectively, demonstrating a reduction of approximately 1 cmH2O for both MEP and MIP in each year.



Peak expiratory flow and peak cough flow

PEF was higher in active than in moderately active elderly, and higher in men than in women (Table 2, p=0.046 and p=0.001, respectively). The linear regression model demonstrated that men showed, on average, 139.5 L/min higher than women.

When comparing PCF with the other variables, a statistically significant difference was found for gender and AAS, with a higher PCF for males (P<0.001) as well as for active participants (p=0.004, Table 2). The correlation coefficient demonstrated a weak and positive correlation between PCF and AAS (r=0.365 and p=0.004). The linear regression analysis demonstrated that men showed on average 113 L/min higher than women, and that active elderly showed on average 43 L/min higher than in moderately active participants (Table 3).

No statistically significant difference was found between PA and PI groups for PEF and PCF values (p=0.175 and p=0.117, respectively).



The present study evaluated the PCF, PEF, MIP and MEP in elderly classified as moderately active or active by the HAP, aiming to verify if the functional level is associated with those variables. Functional level can be defined as the ability of the individual to perform routine activities with varied levels of complexity and energy expenditure. Among this type of activity are the activities of daily living, leisure and sport21. To our knowledge, this is the first study that addressed this matter.

The main result of this study was the presence of a positive correlation between AAS, MEP and MIP (r=0.527, p<0.001, r=0.498, p<0.001, respectively). However, no statistically significant difference was observed for the respiratory muscle strength measurement between elderly who did and those who did not perform regular physical activity. These findings suggest that the ability to perform more complex activities of daily living that involve more energy requirement has an important role in respiratory muscle strength.

In relation to PEF and PCF, the highest values were found for males and for active elderly. This result can be related to the fact that contracting the expiratory muscle is an important phase for coughing, and in our sample male and active elderly showed greater values of expiratory muscle strength than women and moderately active elderly.

Several studies have demonstrated a negative correlation between respiratory muscle strength and variables that are modified by aging3-6,9,25,28-31. This study found a negative correlation between age and MIP (r=-0.359, p=0.005), and a reduction of approximately 1 cmH2O per year on MEP and MIP (regression coefficient = -1 cmH2O and -0.8 cmH2O, respectively) in the study sample. Moreover, men also showed higher MEP and MIP than women (on average, 16.2 cmH2O and 17.2 cmH2O more, respectively). These findings were similar to the ones found in a multicenter study conducted by Enright et al.29 in 1994, who assessed 4443 elderly aged 65 years and over and found a decrease in respiratory muscle strength from 0.8 to 2.7 cmH2O per year, being this loss more important in women.

Some studies have evaluated the influence of physical activity or fitness in pulmonary function and respiratory muscle strength. Cook et al.2 investigated the correlation between functional ability and physical activity, by means of the Katz scale and a specific questionnaire developed for the study, and PEF in 2250 subjects aged 65 years and over. They concluded that individuals who were capable of performing their activities of daily living had higher PEF rates (p<0.0001), in the same way as those who performed regular physical activity (p<0.0001).

In 1999, McConnell and Copestake4 calculated the energy expended by elderly subjects during a four-week period based on a guided diary. The authors found significant correlation between physical activity and MEP and MIP (r=0.67; p=0.032 and r=0.87; p=0.001, respectively).

A sedentary lifestyle combined with the aging process may exacerbate the reduction in both inspiratory and expiratory muscle strength, leading to a reduction in intrathoracic pressure and expiratory flow during cough32. In 2005, Watsford et al.8 evaluated 77 subjects aged over 64 years that were classified as active or inactive. Active participants showed MIP and MEP 14 and 25% higher than inactive participants, respectively. The authors also showed a positive correlation between respiratory muscle strength and maximal oxygen intake (VO2max) in both men (MIP r=0.39: p<0.05 and MEP r=0.50; p<0.05) and women (MIP r=0.54; p<0.05 and MEP r=0.59; p<0.05). Vasconcellos et al.33 also found that MIP and distance walked in the 6 minute walk test were correlated (r=0.44; p=0.005) in elderly women.

As for PCF, this variable is very similar to PEF, being the primary difference between them the closure of the glottis during PCF34. The investigation of PCF is a relatively recent measurement tool that has been used to assess the severity of cases, the risk of pulmonary complications and also as a predictor of successful extubation or decannulation, mainly of patients with neuromuscular diseases18,26,34. Those without neuromuscular diseases who presented respiratory muscle weakness also benefit from this assessment as they are more susceptible to pulmonary complications. Kim, Davenport and Sapienza32 published a study in 2008 that investigated the effect of a four-week expiratory muscle strengthening program on parameters of capsaicin (an active component of pepper) on the induced cough reflex in sedentary elderly. The authors reported an increase on MEP and PEF rates of cough, which was measured by pneumotachograph (p<0.001 for both variables).

Importantly, the fact that the assessment of the physical activity level relied solo on the information given by the participants is a limitation of this study. The procedures used to assess respiratory muscle strength and PEF and PCF variables are effort-dependent and require full cooperation of the participant that underwent the evaluation35; therefore, using the Mini-mental state examination could have contributed to select the participants from those in which the cognitive aspect could affect the understanding. Also, the level of and individual maximal effort during the tests could justify the differences found in each study. Once cough is commonly a reflex event, the best way to determine the effect of the respiratory muscle strength on it would be measuring their strength from a reflex cough34. Another limitation of the present study is the difference between the number of males and females that could have contributed to the absence of difference on MIP between men and women, which would be considered a type II error. However, this study did not aim to assess the influence of gender on cough strength, but the influence of physical activity and functional level on it.

In summary, our results demonstrated that aging is associated with a reduction in inspiratory and expiratory muscle strength. Moreover, the routine activities of living performed by the elderly can have a positive influence on maximum respiratory pressures and PCF. Thus, it seems that as important as maintaining a regular physical activity, such as mentioned in previous studies, is to include more complex tasks in daily life routine. New studies aiming to assess the same variables in inactive elderly classified by the HAP may give us a better understanding of the influence of the functional level and the physical activity on pulmonary function. Furthermore, this study highlights the relevance of PCF as an assessment tool very useful for respiratory physical therapists, and for designing both rehabilitation and prevention of complications programs.



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Correspondence to
Verônica Franco Parreira
Departamento de Fisioterapia, EEFFTO
Av. Presidente Antônio Carlos, 6627, Pampulha
CEP 31.270-901, Belo Horizonte (MG), Brasil

Received: 08/06/2009 - Revised: 03/12/2009 - Accepted: 22/06/2010

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