BrJt Sports Med 1997;31:337-341

Comparison of lung volume in Greek swimmers,land based athletes, and sedentary controls usingallometric scaling

Michael Doherty, Lygeri Dimitriou

AbstractObjective-To compare lung volumes in alarge cross sectional sample of Greekswimmers, land based athletes, and sed-entary controls by means of allometricscaling.Methods-Four hundred and fifty nineasymptomatic Greek children and youngadults (age 10-21 years), including 159swimmers, 130 land based athletes, and170 sedentary controls, performed forcedexpiratory manoeuvres into a portablespirometer. Measurements included forc-ed vital capacity, forced expiratory vol-ume in one second (FEVy1O), and peakexpiratory flow. Body mass and staturewere also measured using standardisedanthropometric techniques.Results-Logarithmic transformationsshowed that In FEVy10 was highly related toIn stature in males and females (r = 0.93and 0.86 respectively, P<0.001) and wereused to determine the exponent in an allo-metric equation which also included ageand age2. Resulting power functions,FEV,IJstatureb, were 0.64 (0.18) litres/m269and 0.33 (0.24) litres/m232 for males andfemales respectively (mean (SE)). Themale and female swimming groups hadlarger FEV1 0 than both land based athletesand sedentary controls (one way analysisof variance, P<0.001). In addition, malenational standard swimmers (n = 38) hadsuperior FEV 1.0 in comparison with malenon-national standard swimmers (n = 24;t test, P<0.05). However, when years ofswimming training was controlled for byanalysis of covariance, the difference inFEV1.0 between the two groups was nolonger evident.Conclusions-Swimmers have superiorFEVy10 independent of stature and age incomparison with both land based athletesand sedentary controls. In addition, malenational standard swimmers have supe-rior FEV1.0 independent of stature and agein comparison with male non-nationalstandard swimmers. When years of train-ing is controlled for, the difference inFEVy10 between the two groups is no longerevident. This suggests that the years ofswimming training and/or the earlier ageat which training begins may have asignificant influence on subsequent FEV1.0and swimming performance. However,because of the cross sectional nature ofthis study, the results do not exclude

genetic endowment as a major determi-nant ofthe superior lung volume observedin swimmers.(BrJ Sports Med 1997;31:337-341)

Keywords: swimming physiology; intensive training;respiratory muscle strength; allometric modelling

The characteristic skeletal features ofswimmersappear at an early age. Swimmers tend to be tallfor their body mass' and have high bi-acromialbreadths for their age group.2 In addition, it hasrepeatedly been shown that static lung volumeand pulmonary diffusing capacity of swimmersare greater than in age- and stature-predictedvalues, sedentary controls,3-7 or highly trainedland based athletes.4 7-11 The relationship be-tween structure and function in swimmingappears self evident. Body length shouldprovide an advantage in starting, turning, andfinishing and long segments have an advantagefor stroking technique."2 In land based exercisethe pulmonary system is usually not consideredto be a limitation to performance.' In addition,longitudinal studies of subjects involved in landbased activities show lung volume to beunaffected by short term training. '17 However,in swimmers there are a number of possiblebeneficial consequences of increased lungvolume.'" 18 These include improved buoyancyresulting in a more streamlined body positionand therefore less drag in the water,' 18increased surface area for gas exchange,'reduced respiratory oxygen cost at any givensubmaximal swimming intensity,5 and an in-creased intrapulmonary pressure which wouldaid expulsion of the blood from the pulmonaryvessels.'9 However, unlike the anthropometricalcharacteristics of swimmers, which have beenshown to be mostly influenced by geneticendowment,20 21 it is unclear whether the supe-rior lung function found in swimmers is due togenetic influences or is the result oftraining.3 8-l 18 There is a considerable ventila-tory strain during swimming, and this appearsto increase the conditioning of the accessorymuscles of the neck and chest wall.'0 This mayincrease maximal static pressure, thus augment-ing the swimmer's ability to inflate and deflatethe lung.'8 22 Alternatively, swimming trainingmay directly enhance lung growth by some, asyet unknown, mechanism.22 This is in contrastwith the general population where it has beenshown that growth in lung volume is entirelydue to growth in body dimensions with noadditional effect of changes in the developmentof physical performance. 14-17 2325

Department of Sportand Exercise Science,University of LutonM DohertyL Dimitriou

Correspondence to:Michael Doherty,Department of Sport andExercise Science, Universityof Luton, Park Square,Luton, Beds LU1 3JU,United Kingdom.

Accepted for publication28 May 1997

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Most of the studies that have investigatedlung volume in swimmers have made compari-sons with either matched controls or predictedvalues." "' Few studies have used an allometricmodelling approach,8 a topic of renewedinterest in sport and exercise science.26 Thistechnique provides a truly dimensionless ex-

pression of data which can be used insubsequent comparisons between groups thatdiffer in body size.27 Therefore the aim of thisstudy was to compare lung volume in a largecross sectional sample of swimmers, land basedathletes, and sedentary controls by means ofallometric scaling.

MethodsFour hundred and fifty nine asymptomaticwhite Greek children and adults (10-21 yearsof age) were tested. Swimmers and land basedathletes were admitted on the criterion oftraining a minimum of three times per week fortheir respective sports. Land based athletesincluded subjects who trained and competed inathletics, basketball, canoeing, and rowing.Sedentary controls were admitted on the crite-rion of not being connected with any particularsport and not having a regular exerciseprogramme (that is, with the exception of par-

ticipating in compulsory physical educationclasses in school). Before testing, informationon subject age, date of birth, and the number ofyears of training (for land based athletes andswimmers) was obtained verbally from the par-ent or coach. Static lung function measure-

ments were performed with a portable trans-

ducer spirometer (Microlab 3300; Cranlea &Co, Birmingham, UK). Subjects performed thetest in a standing position with a nose clip inplace and spirometer held in one hand. After a

maximal inhalation, subjects sealed their lipsaround the mouthpiece and exhaled as hardand as fast as possible.28 Subjects were encour-

aged to continue exhaling for at least one

second so that forced expiratory volume forone second (FEV1,0) could be measured. Testswere repeated a minimum of three times or

until the two highest recorded values-that is,forced vital capacity (FVC) + FEV,0-variedless than 3%. Direct measurements includedFVC (litres), FEVy10 (litres), and peak expira-tory flow (litres/second). The forced expiratoryratio (%) was also calculated ((FEV, O/FVC) x

100). Body mass (kg; Seca 761 scales, ± 0.5 kg;Seca Co., Germany) and stature (m; CranleaJP60 portable stadiometer, + 0.001 m; Cranlea& Co) were also measured using standardisedanthropometric techniques.The testing took place in various stadia,

swimming pools, and state schools in Greecewith the full written permission of the subjectsand their parents, the Greek National Swim-ming Federation, and the Physical EducationDepartment of the Dodekanese County.

STATISTICAL ANALYSIS

Descriptive statistical analysis was performedon all measurements and this was followed byone way analysis of variance to determinedifferences between groups on these measure-

ments. Where a significant F value was

Table 1 Male andfemale subject details (mean (SD))

Swimmers Land based athletes Sedentary

Males Females Males Females Males Females(n=82) (n=78) (n=90) (n=72) (n=66) (n=70)

Age (years) 15.1 (3.0)* 14.5 (2.4) 14.1 (2.6) 14.4 (2.6) 13.8 (2.7) 14.0 (2.5)Stature (m) 1.70 (0.13)t 1.63 (0.10)* 1.64 (0.15) 1.59 (0.10) 1.62 (0.14) 1.57 (0.10)Bodymass (kg) 61.8 (14.8) 51.7 (9.8) 59.0 (15.6) 50.6 (10.3) 56.3 (17.6) 49.2 (10.2)

* Statistically significant difference (one way analysis of variance, P < 0.05) from sedentary controls.t Statistically significant difference (one way analysis of variance, P < 0.05) from land based athletes and sedentary controls.

Table 2 Male lungfunction values as body temperature, pressure and saturation: observed (mean (SE)) and predicted(by gender, stature, age, %) values29

Swimmers (n=82) Land based athletes (n=90) Sedentary (n=66)

Observed Predicted Observed Predicted Observed Predicted

FVC (litres) 4.5 (1.3)* 103* 3.9 (1.3) 96 3.5 (1.1) 90FEV,, (litres) 4.1 (1.2)* 111* 3.4 (1.1) 102 3.1 (0.9) 97FER (%) 90.9 (5.9) - 89.2 (5.2) - 89.9 (5.9) -PEF (litres/second) 488 (135)* 96* 410 (128) 88 381 (111) 83

FVC, forced vital capacity; FEV, 0, forced expiratory volume in one second; FER, forced expiratory ratio; PEF, peak expiratory flow.* Statistically significant difference (one way analysis of variance, P < 0.05) from land based athletes and sedentary controls.

Table 3 Female lung function values as body temperature, pressure and saturation: observed (mean (SE)) and predicted(by gender, stature, age, %o) values2"

Swimmers (n=78) Land based athletes (n=72) Sedentary (n=70)

Observed Predicted Observed Predicted Observed Predicted

FVC (litres) 3.5 (0.8)* 104* 3.3 (0.7)t 96t 2.9 (0.6) 91FEV,, (litres) 3.3 (0.7)* 111* 2.9 (0.6) 99 2.7 (0.6) 102FER (%) 93.4 (5.8) - 91.9 (5.0) - 93.7 (4.7) -PEF (litres/second) 396 (78)* 95* 364 (74)t 91t 329 (85) 83

FVC, forced vital capacity; FEV, ,, forced expiratory volume in one second; FER, forced expiratory ratio; PEF, peak expiratory flow.* Statistically significant difference (one way analysis of variance, P < 0.05) from land based athletes and sedentary controls.t Statistically significant difference (one way analysis of variance, P < 0.05) from sedentary controls.

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Land-based athletes A . *

Sedentary --_-a

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Table 6 Male andfemale FEV,9 statureb * values(mean(SE))

Land basedSwimmers athletes Sedentary

Males 0.63 (0.008)- 0.58 (0.008) 0.57 (0.007)Females 0.71 (0.008)' 0.67 (0.012)' 0.64 (0.091)

* 0.64 (0.18) litres/mr269 and 0.33 (0.24) litres/m232 for malesand females respectively (mean(SE)).a Statistically significant difference (P < 0.05) from land basedathletes and sedentary controls.' Statistically significant difference (P < 0.05) from sedentarycontrols.

A3between the lung function parameters and

° B y o subject characteristics. Logarithmic transfor-mations were performed on FEV,1 and staturein men and women, and these logarithmically

- °̂ transformed data were used to determine theexponent in the following allometric equa-

2620 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2 tion,

Stature (i) FEV,.0 = stature' x exp(c + (d x age) + (e xMale itnvner functional relationshitps between FEV. and stature. age)2 ) E

Swimmers o -Land-based athletes .* *

Sedentary o --0

TO T0

ArP oo

0

1.0 _-

0.5

1.20 1.30 1.40 1.50 1.60Stature (m)

1.70 1.80

Figure 2 Female powerfunctional relationships between FEV,30 and stature.

Table 4 FEV, Istatureb* analysis of variance for males

Degrees of Sum ofSource freedom squares Mean F squares F ratio Probability (P)

Between groups 2 0.65 0.32 23.6 < 0.001Within groups 235 3.23 0.01Total 237 3.88

* 0.64 (0.18) litres/m269 (mean(SE)).

Table 5 FEV, Istatureb* analysis of variance forfemales

Degrees of Sum ofSource freedom squares Mean F squares F ratio Probability (P)

Between groups 2 0.60 0.30 20.7 < 0.001Within groups 219 3.20 0.02Total 221 3.80

* 0.33 (0.24) litres/m2"32 (mean(SE)).

obtained (P<0.05), the post hoc Scheffe's pro-cedure was used to identify significantly differ-ent groups. In order to control for the effects ofstature and age, an allometric modellingapproach was used based on the recommenda-tions of Nevill and Holder.26 This was precededby Pearson Product Moment correlation coef-ficients to determine the degree of relationship

where k, c, d, and e are constants, and E =error term.

Again, to determine if there were statisticaldifferences between swimmers, land based ath-letes, and sedentary controls, a one way analy-sis of variance was performed on the resultingpower function ratios.26 An independent t teston the power function ratios of the male andfemale national standard swimmers and non-national standard swimmers was also per-formed. In addition, an independent t test wasperformed on the number of years of trainingfor national standard swimmers v non-nationalstandard swimmers. Finally, analysis of covari-ance was performed on the power functionratios of the national standard swimmers vnon-national standard swimmers, with years oftraining used as the covariate. The level of sta-tistical significance was set at P<0.05.

ResultsTables 1-3 present the subject characteristics.The results for the different groups are similarto values obtained previously in eitherthe general population24 25 30-32 (for sedentarycontrols and land based athletes) orswimmers.' 311 18 22 3135 As expected, both maleand female swimmers had superior peakexpiratory flow, FVC, and FEV1, comparedwith land based athletes and sedentary controls(figs 1 and 2), but the swimmers were alsotaller than land based athletes and sedentarycontrols. In addition, male swimmers wereolder than male land based athletes and seden-tary controls (table 1).

Pearson Product Moment correlation coeffi-cients showed that ln FEV,.0 was related to Instature in males and females (r = 0.93 and 0.86respectively, P<0.001). When combined withage and age2, the explained variance (R2) inFEV,.0 was 76% and 88% for females andmales respectively. Resulting power functions,FEVLjstatureb, were 0.64 (0.18) litres/mi269 and0.33 (0.24) litres/M232 for males and femalesrespectively (mean (SE)). These exponents arevery similar to values previously reported in theliterature.3032 The subsequent one way analysisof variance on the power functions showedsignificant F values (P<0.001) for both males

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Table 7 Male andfemale FEV,0,values for national and non-national standardswimmers (mean (SE))

National Non-national

Males (n=37) Females (n=24) Males (n=39) Females (n=13)

FEV,3 (litres) 5.02 (0.14)0 3.68 (0.09) 4.20 (0.19) 3.59 (0.08)FEV,3,/statureb* 1.03 (0.022)a 1.11 (0.015) 0.93 (0.023) 1.08 (0.029)

* 0.64 (0.18) litres/M26'9 and 0.33 (0.24) litres/Mr232 for males and females respectively (mean(SE)).aStatistically significant difference (t test, P < 0.05) from data for non-national standard males.

Table 8 Details of male andfemale national and non-national standard swimmers(mean (SD))

National Non-national

Males (n=37) Females (n=24) Males (n=39) Females (n=13)

Age (years) 18.9 (3.7)* 16.1 (3.1) 16.5 (3.8) 16.5 (1.9)Stature (m) 1.79 (0.07)* 1.67 (0.07) 1.73 (0.10) 1.68 (0.06)Body mass (kg) 71.8 (10.4)* 55.4 (8.1) 63.7 (13.1) 56.5 (5.0)Years oftraining 10.5 (3.8)t 7.0 (2.7)t 8.1 (3.1) 4.6 (1.3)

* Statistically significant difference from male non-national standard swimmers (t test, P < 0.05).t Statistically significant difference from non-national standard swimmers (t test, P < 0.01).

Table 9 FEV, 0/statureb* analysis of covariance (years of training = covariate) for maleswimmers

Degrees of Sum of MeanSource freedom squares Square ratio F probability

Years of training 1 0.096 0.096 7.3 > 0.01National/non-national 1 0.017 0.017 1.3 0.26Explained 2 0.174 0.087 6.6 > 0.01Residual 110 1.5 0.013Total 112 1.68 0.014

* 0.64 (0.18) litres/Mi203 (mean(SE)).

Table 10 FEV, ,Istature0 *analysis of covariance (years of training = covariate) forfemale swimmers

Degrees of Sunm of MeanSource freedom squares Square ratio F probability

Years of training 1 0.343 0.343 15.4 > 0.01National/non-national 1 0.019 0.019 0.88 0.35Explained 2 0.362 0.181 8.2 > 0.01Residual 110 2.5 0.022Total 112 2.8 0.014

* 0.33 (0.24) litres/m2 32 (mean(SE)).

and females (tables 4 and 5). The post hocScheffe's procedure showed that the swimminggroup had larger FEV,1 than both land basedathletes and sedentary controls (table 6).The independent t test on the power

function ratios showed that male nationalstandard swimmers had superior FEVI.O com-pared with male non-national standard swim-mers (P<0.05; table 7). However, the nationalstandard swimmers commenced training at ayounger age and had therefore trained for alonger period of time than the non-nationalstandard swimmers (10.5 (3.8) years v 8.1(3.1) years; P<0.05; table 8). When years ofswimming training was controlled for by analy-sis of covariance, the differences in FEVLObetween the two groups was no longer evident(tables 9 and 10).

DiscussionThe results of this study support previous workindicating that lung volume is increased inyoung male and female swimmers comparedwith both sedentary subjects' ' and land basedathletes.4 7-11 Indeed, our results show thatfemale swimmers have absolute lung volumessimilar to male land based athletes and seden-

tary control groups (tables 2 and 3). While landbased athletes and sedentary control groupshave "normal" values in relation to age, stature,and sex, both male and female swimmers haveFEV,1 values about 11% higher than predictedvalues. These results are in agreement withprevious studies that have measured lungvolume in swimmers. 3-8 9-11 18 22 33-35 To whatextent the superior lung volume in swimmers isa consequence of training, and to what extent itmay be due to natural endowment is equivocal.In swimming, the load of the water pressureagainst the chest wall and elevated airwayresistance as the result of immersion couldcomprise a conditioning stimulus as well as therequirement that inspirations must occurrapidly from functional residual capacity dur-ing short intervals between strokes.'8 On theother hand, there is also support in theliterature for a substantial contribution fromgenetic endowment to the enhanced lungfunction in swimmers. Baxter-Jones andHelms9 studied a sample of 231 highly trainedmale swimmers, gymnasts, and soccer and ten-nis players. Of the four sports, the swimmershad the highest initial lung volume in each offive age cohorts (8, 10, 12, 14, 16 years). Hav-ing controlled for factors such as age, stature,body mass, and training hours, multilevelregression analysis showed that the differencein lung size between the sports did not changewith time. Ericksson et af3 have also noted thatincreased lung volume was already present in agroup of 10 year old boys (n = 18) who had justbegun swimming training. Furthermore, otherstudies were unable to detect lung volumeincreases in child swimmers after six or sevenmonths of training.34 3 Because of the crosssectional nature of the present study, the resultscannot exclude genetic endowment as a majordeterminant of the superior lung volumeobserved in elite swimmers. Zinman andGaultier22 have suggested that to differentiatenatural endowment from adaptive growth, it isnecessary to examine the mechanical charac-teristics of the respiratory system of swimmersin more detail. Their work brings attention tothe disproportionate development of air spacesin normal children, and this development hasbeen noted to be even more pronounced as aresult of adaptive growth in high altitudedwellers.36 Cotes37 points out that the increasedlung volume observed in residents of high alti-tude may be the direct consequence of a com-bination of hypoxaemia and a high level ofhabitual physical activity during childhoodrather than the stress of hypoxaemia alone.Documentation of a greater disproportionatedevelopment of air spaces in swimmers com-pared with controls would support the hypoth-esis that swimmers have larger lung volume asthe result of adaptive growth rather thangenetic endowment.22The results further suggest that the most

successful male swimmers-that is, the na-

tional standard swimmers have larger lungvolumes than non-national standard swim-mers. This appears to be the first instance thatsuch a difference between elite and subeliteswimmers has been highlighted. A possible

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reason for the difference between the twogroups is an increased strength of the respira-tory musculature, a factor that contributes toforced manoeuvres, since there is evidence of apositive relationship between upper-body stren-gth and swim performance.38 Further analysisof the data showed that, when years of trainingwas controlled for by analysis of covariance, thedifferences in FEV1.0 between the two groupswas no longer evident. This suggests that thenumber of years of swimming training and/orthe earlier age at which swimming trainingbegins may have a significant bearing onsubsequent FEV,10 and swimming perform-ance. Interestingly, these differences were notevident between the female national andnon-national standard swimmers. It is knownthat in the general population, muscle strengthin itself explains the apparent "acceleration" inmale lung volume with increased stature afterpuberty,20 and it may be that this also holds truefor male and female swimmers. The inclusionof a measurement of respiratory musclestrength might therefore be a useful addition tofuture studies of lung volume of elite vnon-elite male and female swimming groups.

In summary, our results support previouswork that suggests that swimmers have supe-rior FEV1.0 independent of age and stature incomparison with both land based athletes andsedentary controls. In addition, male nationalstandard swimmers were shown to havesuperior FEV1 0 independent of age and staturein comparison with male non-national stand-ard swimmers. When years of training wascontrolled for, the difference in FEV1.0 betweenthese two groups was no longer evident. Thissuggests that the years of swimming trainingand/or the earlier age at which training beginsmay have a significant influence on subsequentFEV1.0 and swimming performance. However,until additional longitudinal studies are com-pleted examining selection, respiratory musclestrength, and training patterns (includingtraining duration and intensity) in more detail,the relative contribution of genetic endowmentand training to enhanced lung volume inswimmers will remain unclear.

The authors express their appreciation to Michael Hughes andPirkko Korkia (University of Luton) for their critical review ofthe manuscript.

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