Gender Differences in Pulmonary Function Measured In and Out of the Water in Trained Swimmers

Department of Physical Education and Sports Science at Serres
Aristotle University of Thessaloniki
62110 Serres, Greece


Corresponding Author

Michalis Sambanis, Ph.D.
Assistant Professor
Department of Physical Education and Sports Science at Serres
Aristotle University of Thessaloniki
Agios Ioannis, 62110 Serres
Greece
Tel: +30-2310-991040 (off)
Email: sampanis@phed-sr.auth.gr

INTRODUCTION
Swimming is a popular recreational physical activity and a high-energy demanding sport at the competitive level. Because water is about 800 times as dense as air and water resistance is approximately 12 times greater than air resistance, the locomotion in water occurs at a much slower speed and it requires more energy and effort (DiPrampero, 1986). When exercise takes place on dry land, all physiological systems of the body are greatly affected by the force of gravity, yet the air resistance is low. In contrast, when the body is immersed and moved in water, the body is instead affected by the buoyancy of the water. Essentially the density of the water and the buoyancy of the body counteract the effect of gravity.

Large lung volumes and great respiratory functional capacity constitute important factors affecting swimming performance (Andrew, Beecklake, Guleria, & Bates, 1972; Blimkie, 1992; Engstrom, Ericksson, Karlberg, Saltin, & Thoren, 1971). The efficiency of the respiratory system presents significant limitations on the body’s ability to perform exercise due to the effects of the increased work of breathing, respiratory muscle fatigue, and dyspnoea (Zinmam & Gaultier, 1986; Vrabas et al., 1999). Respiratory system limitations can impact exercise performance in highly trained individuals (Boutellier, Buchel, Kundert, & Spengler, 1992), especially at high intensities, where the increased work of breathing results in compromised exercise performance (Harms, Wetter, St Croix, Pegelow, & Dempsey, 2000).

In the course of aerobic exercise, as is the case in training for competitive swimming, considerable adaptations in the respiratory muscles are observed, thereby increasing their endurance and strength (O’Kroy, Loy, & Coast, 1992). In addition, the rates of respiratory parameters are improved. For example, vital capacity (VC) is enhanced due to the increase in strength of the respiratory muscles as well as the elasticity of the thoracic cavity and of the lungs (Dempsey, Johnson, & Kurt, 1990; Edlund et al., 1986; Keens, Krastins, & Wannamaker, 1977). Similar changes are observed in forced vital capacity (FVC) and forced expiratory volume at one second (FEV1) (Sambanis, 2006).

A considerable number of studies have examined the effects of exercise on the pulmonary function. Nonetheless, there are relatively few studies that have investigated the effect of water pressure on the pulmonary function in swimmers (Vaccaro & Clarke, 1978). Therefore, the purpose of this study was to examine whether there are differences in pulmonary function in and out of the water in young swimmers and whether any potential differences are gender-related.

MATERIALS AND METHODS
Subjects
Twenty trained swimmers (10 male and 10 female, aged 16-20 years) recruited from Greek swimming clubs were participated in the study. All subjects were healthy, free of any acute or chronic illness and there were not under any form of medication. Written informed consent to participate in the study was provided by the adult subjects as well as the younger subjects and their parents after they were informed of all risks, discomforts, and benefits involved in the study. All experimental procedures were performed in accordance with the European Union guidelines on research with human subjects (Helsinki Declaration) as well as the policy statement of the American College of Sports Medicine on research with human subjects as published by Medicine and Science in Sports and Exercise. The characteristics of the subjects are shown in Table 1.

Table 1. Anthropometric characteristics of the subjects (mean ± SD)

	Males (n = 10)				Females (n = 10)
Age (y)	18.3	±	2.2		18.6	±	2.6
Height (cm)	178.2	±	7.3		167.1	±	5.5#
Body weight (kg)	65.7	±	9.8		57.8	±	4.8*
Body Mass Index (kg/m	20.6	±	1.8		20.7	±	1.1
Training experience (y)	10.0	±	4.2		12.7	±	3.5

#P < 0.05, significantly different compared to male swimmers
*P < 0.001, significantly different compared to male swimmers

Pulmonary function measurements
To assess pulmonary function, all swimmers were subjected to respiratory measurements at rest, both in and out of the water, by the means of a portable electronic spirometer (Pony Graphic, Cosmed, Rome, Italy). The “wet” measurements took place in an indoor swimming pool. The subjects assuming the front crawl position were lay prone on a wooden board (length 2 m, width 0.8 m) which had been placed in the swimming pool. The subjects were submerged in the water until their body was fully covered expect for the head that remained out of the water. The “dry” measures were performed in the same indoor facility in an area located proximal to the swimming pool. The subjects lay prone on the wooden board thus simulating the front crawl position normally assumed in the water. The participants after they had been familiarized with the spirometry test, they performed two trials of maximal effort in each experimental condition (i.e., in and out of the water). The resting time between trials was five minutes. The best trial was recorded. The respiratory parameters measured were the following: vital capacity (VC), forced vital capacity (FVC), forced expiratory volume at one second (FEV1), indicator Tiffeneau (FEV1/FVC), peak expiratory flow (PEF), and forced expiratory flow rate at 0.25-0.75 sec (FEF 25-75).

Swimming performance tests
Swimming performance tests took place in the same indoor swimming pool described above. The subjects at three occasions swam in a random order three distances, i.e. 50, 100 and 200 m front crawl at maximal effort. Each trial was performed after a controlled warm-up (~600 m front-crawl swim) at medium intensity. The time required to complete each test was recorded by a trainer using a hand stopwatch. Heart rate was measured at rest and immediately after the completion of each test through the arterial pulse rate of the radialis artery using the 30 s counting method. Subsequently, the pulse count was then doubled so as to estimate the heart rate per minute. The subjective perception of the effort by the swimmers was also measured using the scale of Borg (1982). The water temperature during the swimming performance tests and spirometric measurements was kept at 25–26 ºC, which was similar to the air temperature recorded in the indoor facility.

Statistical Analysis
Data were analyzed using SPSS, version 14 (SPSS, Chicago, IL, USA). To evaluate any differences of treatment, gender or treatment by gender interaction in respiratory parameters, a two-way (treatment  gender) ANOVA was applied. Pairwise comparisons between parameters measured out of and in the water within the same group as well as parameters measured in males and females at the same condition were performed through simple main effect analysis. To evaluate any differences between male and female subjects in anthropometric characteristics, physiological responses and performance, an independent Student’s t test was applied. The level of statistical significance was set at P < 0.05.

RESULTS
The anthropometric and physiological characteristics of the subjects as well as the performance in the swimming tests were presented in Tables 1 and 2. Significant differences in height, body weight and performance in 50, 100, and 200 m front-crawl test between male and female swimmers were found (P < 0.05).

Table 2. Performance and physiological responses of the swimmers (mean ± SD)

	Males (n = 10)				Females (n = 10)
Heart rate (beats∙min–1) 50 m front-crawl	174.8	±	11.4		176.3	±	10.9
100 m front-crawl	175.2	±	11.1		176.7	±	10.8
200 m front-crawl	177.5	±	3.4		176.9	±	4.4
Mean time (s) 50 m front-crawl	30.1	±	1.3		32.2	±	1.1*
100 m front-crawl	63.9	±	3.2		69.2	±	1.8*
200 m front-crawl	140.5	±	7.4		151.1	±	4.6*
Fatigue (Borg scale) 50 m front-crawl	16.2	±	1.1		16.0	±	1.2
100 m front-crawl	16.4	±	1.5		16.3	±	1.3
200 m front-crawl	16.1	±	1.6		16.3	±	1.4

*P < 0.001, significantly different compared to male swimmers

With respect to vital capacity, there were significant main effects of treatment (P < 0.05) and gender (P < 0.001), but there was no significant treatment-by-gender interaction (P > 0.05). In males, VC (Fig. 1A) was lower in the water compared to the respective value measured out of the water (P < 0.001). Females had lower VC compared to respective values of males both out of (P < 0.001) and in the water (P < 0.05). In forced vital capacity, there were significant main effects of treatment (P < 0.05) and gender (P < 0.001), but there was no significant treatment-by-gender interaction (P > 0.05). In males, FVC (Fig. 1B) was lower in the water compared to the respective value measured out of the water (P < 0.05). Females had lower FVC compared to respective values of males both out of (P < 0.001) and in the water (P < 0.05).

Fig. 1. A) Vital capacity (VC) and B) forced vital capacity (FVC) measured out of water (open bars) and in the water (solid bars) in male and female swimmers (mean ± SD). *, Significantly different from the respective value measured out of water within the same group (P < 0.05). #, Significantly different from the respective value measured in males at the same condition (P < 0.05).

Regarding forced expiratory volume at one second, there were significant main effects of gender (P < 0.001), marginally no significant main effects of treatment (P = 0.069) and no significant treatment-by-gender interaction (P > 0.05). In males, FEV1 (Fig. 2A) had trend (P = 0.080) to be lower in the water compared to the respective value measured out of the water. Females (Fig. 2A) had lower FEV1 compared to respective values of males both out of (P < 0.001) and in the water (P < 0.01). No significant (P > 0.05) main effects of treatment, gender or treatment-by-gender interaction were observed for FEV1/FVC ratio (Fig. 2B).

Fig. 2. A) Forced expiratory volume at one second (FEV1), and B) indicator Tiffeneau (FEV1/FVC) measured out of water (open bars) and in the water (solid bars) in male and female swimmers (mean ± SD). #, Significantly different from the respective value measured in males at the same condition (P < 0.05).

With regard to peak expiratory flow, there were only significant main effects of gender (P < 0.001) but no significant main effects of treatment or treatment-by-gender interaction (P > 0.05). Females (Fig. 3A) had lower PEF compared to respective values of males both out of (P < 0.01) and in the water (P < 0.01). Similarly for forced expiratory flow rate at 0.25-0.75 sec, there were only significant main effects of gender (P < 0.001) but no significant main effects of treatment or treatment-by-gender interaction (P > 0.05). Females (Fig. 3B) had lower FEF 25-75 compared to respective values of males both out of (P < 0.001) and in the water (P < 0.001).

Fig. 3. A) Peak expiratory flow (PEF) and B) forced expiratory flow rate at 0.25-0.75 sec (FEF 25-75) measured out of water (open bars) and in the water (solid bars) in male and female swimmers (mean ± SD). #, Significantly different from the respective value measured in males at the same condition (P < 0.05).

DISCUSSION

Our data indicate that during the testing in the water at rest, the functional capacity of the respiratory system is limited in males only, as shown by the decreased VC, FVC and FEV1. As expected, females had lower values in all parameters compared to respective values of the males, but the pulmonary function in female swimmers was not affected in the water at rest. More specifically, as reflected by the changes in the rates of respiratory parameters in the water compared to values measured out of the water, in males there was a decrease in VC by 13.32%, FVC by 13.14%, FEV1 by 10%. In females, there was a decrease in VC by 7.68%, FVC by 5.30% and FEV1 by 5.90%. The changes in all other respiratory parameters were small and insignificant.

For same volumes of water and air, the water has bigger mass. The pressure of water is felt by the swimmer and influences mainly the points that contain air, such as are the thorax, the lungs, the ears and elsewhere. According to the literature, the thorax found hardly under the surface of water is little pressed in such degree, that the VC is decreased at 9% roughly. Breathing, mainly the inhalation phase, may be affected as the thorax presses on the opposite direction to the pressure exerted by water. Still the hydrostatic pressure presses the surface veins, thus resulting in distribution of blood which is increased in the centre and decreased in the region.

Furthermore, the hydrostatic pressure results in a restricted inspiratory force, thus reducing lung capacity and VC. A reduction in VC by 3-9 % has been reported when individuals are immersed to the level of the xiphoid process (Agostoni, Gurtner, Torri, & Rahn, 1966). Decreases in VC, functional residual capacity and expiratory reserve volume have been attributed to the combined effects of hydrostatic chest compression and increased intrathoracic blood volume. Similar changes occur in VC and expiratory reverse volume, the progressive increase in chest compression being represented by a rightward shift of the volume-pressure curve (Chu & Rhodes, 2001). The level of immersion, therefore, is a key influence in determining alterations in pulmonary parameters.

The swimmers’ performance was assessed in the 50, 100 and 200 m front crawl tests. Furthermore the swimmers’ perceived exertion rate was classified on the Borg scale at the end of 50, 100 and 200 m swimming performance tests. In all three swimming performance tests and for both male and female swimmers, the subjective perception of the effort according to Borg scale was about 16, which is considered high. Specifically, the swimmers of male rated their level of effort at 16 and of female at 15. The level of these rates corresponds to about 80-95% of the HR max of the particular age, which is considered a level of sub-maximal intensity (McArdle, Katch, & Katch, 2000). The HR max recorded immediately after the swimming performance tests corresponds to 80-95% of HR max according to the age of the swimmers of the sample in question, thus confirming the values of Borg’s perceived exertion scale. This particular level of intensity is deemed capable of bringing about an improvement in the anaerobic capacity. Even though exercise taken for 10 to 20 minutes at the 80-95% level of intensity leads to an improvement of the anaerobic capacity (McArdle et al., 2000).

According to Bye, Farkas, and Roussos (1983) the respiratory muscles are subject to fatigue during high intensity exercise (>85% VO2 max). Lomax and McConnell (2003) demonstrated that a single 200 metre front-crawl swim corresponding to 90-95% of race pace was sufficient to induce inspiratory muscle fatigue. It is possible that exercise training results in several positive adaptations that could affect respiratory muscle fatigue (Volianitis et al., 2001). Appropriate exercise intensity is an important consideration for the development and maintenance of performance during land-based training (Wenger & Bell, 1986). Proper training intensity seems to be even more significant because the circulatory responses of running in deep water differ from those of on-land running (DiPrampero, 1986; Wenger & Bell, 1986; Brown, Chitwood, Beason, & McLemore, 1996). In water that is chest deep or higher, hydrostatic pressure exerted by the water causes a redistribution of blood volume away from the extremities, resulting in greater amounts of blood in the thorax region (Christie et al., 1990). The central shift in blood volume increases the amount of blood ejected from the heart per beat (stroke volume), thus producing a compensatory reduction in heart rate (HR) during deep water exercise. Studies report HR responses to be approximately 10-12 beats lower than those achieved during land running at matched sub-maximal intensities (Ritchie & Hopkins, 1991; Frangolias & Rhodes, 1995).

The effect of water in the human organism is also the alleviation of cardiac frequency from the moment that the body of the swimmer remains for more from 10 seconds under the water surface. The alleviation becomes bigger at the moment that the body is sunk entirely and the swimmer keeps air in the lungs, while he remains underwater. However, other investigations observed no differences in HR between exercise modes (Bishop, Frazier, Smith, & Jacobs, 1989; Michaud, Rodriquez-Zayas, Andres, Flynn, & Lambert, 1995; DeMaere & Rudy, 1997). Factors such as familiarity with deep water (Frangolias & Rhodes, 1995), altered running technique (Wilber & Brennan, 1993), differences in water temperature (Brown et al., 1996), and exercise protocol (DeMaere & Rudy, 1997) have contributed to this discrepancy in the literature. DeMaere and Rudy (1997) tested the acute metabolic responses of cross-country runners who were currently incorporating deep water running into their training routines.

CONCLUSION

Our data indicate that pulmonary function at rest may be compromised in the water compared to that measured out of the water in male, but not in female, swimmers. The decrease in respiratory function may have a negative effect on the swimming performance. A possible alteration in pulmonary function during exercise in the water compared to that measured out of the water for either gender is yet to be elucidated. In any case, the optimal function of the respiratory system may be minimizing the potential negative effect of water submersion on swimming performance.

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