Better function of every system in the human body is achieved by regular exercise. Muscular strength in general (including respiratory muscles) is developed by systematic training, so it is assumed that it has a positive effect on the lung function. Recent studies have shown that athletes have larger capacity of the respiratory system when compared to their age-matched sedentary controls.1 It was also observed that some particular sport disciplines improve the lung function better than others, these include swimming, and, as recently reported, basketball, water polo and rowing.2–4 Swimmers also achieve larger lung volumes and higher functional cardiorespiratory system capacity compared to other athletes.5,6 However, the impact of swimming (as a specific type of sport) on the development of the lung function has not yet been clearly established.

Aerobic exercise enables efficientt lung oxygen uptake, making the lungs work effectively by activating large muscle groups and raising the heart rate. In addition, swimmers perform strenuous underwater exercise holding their breath for prolonged periods.3 Respiratory muscles, including swimmer's diaphragm, are required to develop higher pressure, resulting from water immersion during the respiratory cycle, leading to functional strengthening of the muscles, as well as improvement in the chest wall elasticity, resulting in higher level of the lung function.3,6 However, the possibility that hereditary factors may have an influence on the larger lung volumes in swimmers cannot be ruled out. Recent studies have shown that swimmers present larger lungs, which could not be attributed to changes in height, fat free mass, maximal respiratory mouth pressures, alveolar distensibility, age at start of training, years of training, training time per week, distance per session, sternal length, or chest depth at total lung capacity.7

In the land-based sport activities, respiratory system is not usually considered to be a limitation factor for physical activity, but no extensive studies have been conducted to approve or rebut this statement in general.1,8

Spirometry is the crucial respiratory function assessment test, as a standardized and reproducible method for estimating the respiratory mechanism and pulmonary ventilation. Spirometric values determined in athletes usually refer to standards (i.e. standardized predicted values) for the average population of healthy subjects, as recommended by international organizations, such as the European Respiration Society (ERS), European Commonwealth of Coal and Steel (ECCS) or the American Thoracic Society (ATS).9,10,11

The first aim of this study was to compare lung volumes in elite athletes, e.g. swimmers (representing water-based sport activity) and football players (representing land-based sport activity) and their age- and sex-matched sedentary controls; the second aim was to examine whether the training factors have an influence on the pulmonary function in swimmers in controlling anthropometric features.

Age at the beginning of training was 9.4 (2.6) for swimmers and 8.4 (2.1) for football players, which significantly differed (p=0.035). Training period was 12.8 (3.0) years for swimmers and 11.9 (3.9) years for football players with no statistical difference. The amount of personal training was 22.0 (7.9) and 21.1 (5.2)h per week for swimmers and football players, respectively (with no significant difference).

Patient characteristics are given in Table 1. Groups did not differ in relation to age and body fat. Both groups of athletes were significantly taller and weighed more than the control group. Among athletes, swimmers were taller and heavier than the football players. Athletes did not differ in BMI, but controls had higher BMI than the football players.

Mean values of the measured spirometric indices are shown in Table 2. Both groups of athletes had significantly higher values of the VC, FVC and FEV1 (measured in liters) than the control group. Swimmers had higher values for all of the mentioned indices in comparison to football players. The FEV1/FVC ratio was statistically higher in swimmers compared to both the football players and the control group. There was no difference in measured values of PEF and MVV in the examined groups.

Measuring the percentage of the predicted spirometric values, swimmers had statistically higher values of VC, FVC, FEV1 and FEV1/FVC, compared to both the football players and the controls, as the latter two showed no in-between differences in the above mentioned parameters.

There was significant positive correlation for each of the following anthropometric features: age, body weight and body height and each of the following pulmonary parameters: VC, FVC, FEV1 and PEF when evaluated separately for swimmers, football players and the control group. Age, body weight and body height also positively correlated with MVV in footballers and controls, but not in the group of swimmers. On the other hand, negative correlation was found between FEV1/FVC and age, body weight and body height for each of the three investigated groups.

The influence of training factors on the pulmonary function indices in swimmers, when controlled for the anthropometric features, is shown in Table 3. Levene's test was used to pretest homogeneity of the variance and showed that the error variance of the dependent variable was equal across groups. The ANCOVA interaction test was run afterwards, showing that there was no training effect by anthropometric features on pulmonar capacity. Finally, the ANCOVA main test was used to evaluate the influence of training on the pulmonary function indices when controlled for the anthropometric features and showed that there was no influence of any of the following training factors: period of time, age at the beginning of training and weekly amount of personal training on the percentage of the predicted spirometric values: VC, FVC, FEV1 and FEV1/FVC in swimmers.

Higher volumes of VC, FVC and FEV1 were found in swimmers compared to both the football players and the control group (measured in liters and in percentages). The results of the present study support the previously published work which showed increased lung volumes in swimmers compared to land based sport disciplines and sedentary controls.5,12,13 In our study, higher lung volumes were found in football players compared to their sedentary counterparts when measured in liters, but no difference was observed in percentages. The present study supports the idea that physical training has a positive impact on the lung ventilatory function, as reported by other studies.2,14,15 The next question is whether larger lung volumes and capacities in athletes are due to their previously determined anthropometric features (height and weight), or due to training.5,7

It was previously reported that swimmers tend to be taller and to have higher bi-acromial breadths than their peers with the same body weight.5 Indeed, the swimmers in our study were taller and heavier than both football players and controls, and had greater lung volumes, accordingly. Anthropometric features could have provided advantages in numerous training techniques, leading to strengthening of the respiratory muscles and improving the lung function in swimmers, in addition to swimming itself.16,17 So, the question arises as to whether larger lung volumes in swimmers are due to their genetics or are developed by training.18,19 Prior studies reported that swimmer's anthropometric characteristics are mostly influenced by their genetic inheritance.5 This is likely to be true, bearing in mind the possibility that swimmers perform better and succeed in this specific type of sport simply because they are positively selected, because they were born with appropriate characteristics.

Our study adds to positive correlation between anthropometric features and respiratory function parameters, as was shown in each of our three investigated groups. Excluding the influence of anthropometric indices, we have found that training factors (training period, age at the beginning of training and weekly amount of personal training) did not influence the lung volumes in swimmers. Furthermore, despite the fact that football players started with intensive training earlier than swimmers (at age of 8.4 vs 9.4), percentages of their lung volumes were lower than that of swimmers and did not differ from the control group.

Besides age, sex, race, height and weight, pulmonary function depends on numerous factors in physically normal individuals: the balance between lung recoil and chest elasticity, (determining the mid-position at the end of spontaneous expiration and the coordinated neuro-muscular function to maintenance the effort); strength of the thoracic and abdominal muscles, individual posture and lung elasticity. Unlike other sports, swimming activates the whole body system muscles, with excessive usage of the chest wall and abdominal muscles, characterized by periods of prolonged holding the breath causing intermittent hypoxia, as a result of the specific way of training. Swimming also differs from other sport disciplines in numerous ways; it is performed in the horizontal position compared to the other sports’ vertical posture, external pressure is higher because the density of the surrounding medium is higher than that of air; and also the water heat conduction is higher than that of air.20–23

The authors have no conflicts of interest to declare.