Faculty of Sport, University of Ljubljana, ISSN 1318-2269  65
Božena Ostrowska
1 
Jaroslaw Domaradzki
2*  
Krystyna Rožek-Mroz
3
DIFFERENTIATION AND SEXUAL 
DIMORPHISM OF CHILDREN’S 
MORPHOLOGICAL FEATURES AGAINST A 
BACKGROUND OF PRACTISING SWIMMING
DIFERENCIACIJA IN SPOLNI DIMORFIZEM 
V MORFOLOŠKIH ZNAČILNOSTIH OTROK 
V ODVISNOSTI OD TRENIRANJA PLAV ANJA
Abstract
Sport training is one of factors which can cause changes 
in morphology of young people. The lack of uniform 
methods in the training of swimming in terms of organ-
ism and strength persuaded the authors to tackle this 
problem. The aim of the study was to assess whether an 
increase in the number of swimming hours affects the 
development of somatic and morphological parameters 
of the body. The second problem was to determine 
sexual dimorphism and its contribution to shaping of 
inter-group differences. The research was conducted on 
a sample of 160 pupils from primary school. Children 
participating in the research were divided into 4 
groups (n = 40): swimming boys and swimming girls, 
non-swimming boys and non-swimming girls. Many 
somatic measurements were taken, such as: body mass 
and height, girths, depths and lengths of extremities 
and chest. Next, the groups were compared in order to 
establish the influence of swimming effort on biological 
growth of children. ANOVA and post-hoc Tukey tests 
were used to estimate differences between groups. 
The authors suppose that the researched factor affects 
some of the somatic measurements. The established 
differences between the groups of swimming and 
non-swimming children partially overlap with those 
obser ve d by ot her aut hor s. Howe ver, t he se obser vat ion s 
do not concern the basic body measures such as height 
and body mass.
Key words: sport swimming, somatic parameters, 
physical effort, sexual dimorphism
1  
Department of Physiotherapy, University School 
of Physical Education, Wroclaw, Poland
2  
Department of Human Kinetics, University School 
of Physical Education, Wroclaw, Poland
3  
Department of Physiotherapy in Conservative 
Medicine and Surgery, University School of 
Physical Education, Wroclaw, Poland
Izvleček
Športno treniranje je eden od dejavnikov, ki lahko 
povzročijo spremembe v morfologiji mladega telesa. 
Pomanjkanje enotnih metod pri treniranju plavanja 
je avtorje spodbudilo k raziskovanju tega vprašanja. 
Namen študije je bil oceniti, ali večje število ur plavanja 
vpliva na razvoj somatskih in morfoloških telesnih 
parametrov. Drugi problem je predstavljala določitev 
spolnega dimorfizma in njegovega vpliva na nastanek 
razlik med skupinami. Raziskava je potekala na vzorcu 
160 učencev osnovne šole. Otroci, ki so sodelovali v 
raziskavi, so bili razdeljeni v 4 skupine (n = 40): dečki 
plavalci, deklice plavalke, dečki neplavalci in deklice 
neplavalke. Opravljene so bile naslednje somatske 
meritve: telesna masa in višina ter obseg, širina in 
dolžina okončin ter prsnega koša. Nato smo skupine 
primerjali, da bi ugotovili vpliv napora med plavanjem 
na biološko rast otrok. Za ugotavljanje vpliva napora 
med plavanjem na biološko rast otrok smo uporabili 
ANOVO in post-hoc Tukeyeve teste. Avtorji domnevajo, 
da raziskovani dejavnik vpliva na nekatere somatske 
meritve. Ugotovljene razlike med skupinami plavalcev 
in neplavalcev so delno sovpadale z ugotovitvami drugih 
avtorjev, vendar pa se izsledki ne nanašajo na osnovne 
telesne meritve, kot sta višina in telesna masa.
Ključne besede: športno plavanje, somatski parametri, 
telesni napor, spolni dimorfizem
Corresponding author: 
Department of Human Kinetics
University School of Physical Education
al. Ignacego Jana Paderewskiego 35
51-612 Wroclaw, Poland
Tel.: +48713473365, Fax.: +48713473034
E-mail: yardo@awf.wroc.pl
 Kinesiologia Slovenica, 11, 1, 65–78 (2005)

66 Differentiation and sexual dimorphism due to practising swimming Kinesiologia Slovenica, 11, 1, 65–78 (2005) 
Introduction
Somatic and functional development of children and youth is influenced by different factors, 
forming a human ecological niche. Analyses of environmental determinants most frequently 
cover the effects of “natural” factors in relation to bio-geographical and socio-economic condi-
tions of living. Determined by genotype, development trends are under influence of the actions 
taken by humans. External modifiers may positively and negatively influence the formation 
of biological features/characteristics. Researchers are particularly interested in observing the 
phenomena that occur in organism during interaction with external factors. 
One of the factors is practising sport. The motion is a basic attribute of life. Therefore, motion 
activity accompanies man from conception. As we are so strongly bound to motion activity dur-
ing our life, we do not think about its essence. This cognition only appears in special situations, 
when a specific motion form becomes a desirable value e.g. during practising of sport (Szopa, 
Mleczko, & Žak, 1996). Monitoring how increased quantity of movement impacts on children’s 
organism in progressive development phase reveals that multidirectional changes occur in a 
young organism (Benefice, Mercier, Guerin, & Prefaut, 1990; Courteix, Obert, Lecoq, Guenon, & 
Koch, 19 97). Biolog ic a l a fter-effec t s of over-t r a i n i ng , such a s os si fic at ion of epiphysia l c a r t i la ge 
or hindering of body's growth, are widely known. On the other hand, some persons are more 
susceptible to the negative impacts of training. In the face of this fact, selection is very important 
(Leone, Lariviere, & Comtois, 2002). 
All actions connected with sport of children and youth should take into account the aspects of 
biological development. Prognoses of development functional abilities should be made based on 
development parameters, depending on training only to a small extent. Foresight of development 
abilities and selection should be based on some stable features that are only to a limited extent 
influenced by training (Duche, Falgairette, Bedu, Lac, Robert, & Coudert, 1993). These features 
a r e d e t e r m i n e d by he r e d it a r y f a c t or s a s we l l a s i n n at e a bi l it i e s . At t he b e g i n n i n g of t r a i n i n g h i g h 
levels of these factors predetermine mastery in the future. Among other things there are also 
height and maximal work capacity (MWC). 
Training is a very strong stimulus affecting the organism status. It must be remembered that 
during the development phase, an organism develops under the influence of physical exercises. 
By crossing the limits of functional adaptation, one may upset the biological equilibrium and 
cause developmental irregularities or disproportions. The child’s organism can develop in one 
direction e.g. excessive muscle mass at the expense of impairments such as low height or poor 
organism function. In extreme cases, excessive exploitation of biological force of children can 
bring about changes in their sexual maturation. 
In sport practice various forms of selection for practising sport occur, such as natural selection, 
intuitive selection and guided selection. In historical terms, the oldest but still essential form of 
selection is spontaneous desire of the child to practice a specific sport. This kind of decision is 
triggered by own inclination, some great successes of the national team and results of competitions 
with schoolmates (Czabanski & Filon, 1991; Dziedziczak & Witkowski, 1998). Coaches have selected 
young athletes on the basis of recently taken measures of various quantities. In their opinion, this 
method is more objective than natural selection. The above case involves a guided selection which 
is substantiated by research. This method makes possible the evaluation of essential parameters for 
youth and enables drawing of conclusions about youth’ s predisposition to specific sport (Damsgaard, 
Bencke, Matthiesen, Petersen, & Muller, 2000; Malina, Meleski, & Shoup, 1982).

Differentiation and sexual dimorphism due to practising swimming 67 Kinesiologia Slovenica, 11, 1, 65–78 (2005)
Th e l o n g e r t h e p e r i o d o f m e a s u r e m e n t s a n d o b s e r v a t i o n s o f i n d i v i d u a l t r a i n i n g s t a g e s , t h e h i g h e r 
the effectiveness of selection (Baxter-Jones, Helms, Maffulli, & Baines-Preece, 1995; Chomiak, 
1994; Saczuk, Poplawska, & Wilczewski, 1998). Having in mind that increased doses of training 
impact on children’s morphological development, the aim of the research was to assess physical 
development of swimming children. We also wanted to establish whether an increase in the 
number of swimming hours affects the development of somatic and morphological body traits. 
The second problem is to determine a sexual dimorphism and its participation in shaping of 
inter-group differences. In an indirect way , we want to establish, if swimming training can reduce 
differences between genders.
METHOD
Participants
The research into some of the morphological traits of school children was carried out on a sample 
of 160 pupils from selected primary schools in Wroclaw, Poland. The children participating 
in the study were divided in the following two groups (80 pupils each): swimming children 
(experimental group) and non-swimming children (control group). Each group was further 
divided by age and gender.
The experimental group consisted of 11- and 12-year old pupils attending the 5
th
 and 6
th
 grades 
of t he Pr i ma r y S chool No. 72 i n Wroclaw. The g roup of boys a ged 11 consisted of ch i ld ren f rom 
10.51 to 11.50 years old (M = 11.04 yrs, SD = 0.29 yrs) and the group of boys aged 12 consisted 
of children from 11.51 to 12.50 years old (M = 12.06 yrs, SD = 0.27 yrs). The same methodology 
applied to the groups of girls (11 years old: M = 11.11 yrs, SD = 0.22 yrs; 12 years old: M = 12.09 
yrs, SD = 0.27yrs). All of the studied pupils had been members of the swimming clubs Šlask and 
Juwenia in Wroclaw for 2-3 years. The children spent, on average, from 12 to 18 hours a week in 
the swimming pool.
The control group consisted of 80 pupils. The same as in the experimental group, the control 
group consisted of 11- and 12-year old pupils attending 5
th
 and 6
th
 grades, except that their 
school was not a sports school. The group of boys aged 11 consisted of children from 10.51 to 
11.50 years (M = 11.09 yrs, SD = 0.27 yrs). The group of boys aged 12 consisted of children from 
11.51 to 12.50 years (M = 12.11 yrs, SD = 0.31yrs). The same methodology applied to the groups 
of girls (11 years old: M = 11.13 yrs, SD = 0.24 yrs; 12 years old: M = 12.05 yrs, SD = 0.22 yrs). 
The children in the control group had never practised sport professionally. The group consisted 
of pupils from the Primary School No. 113 in Wroclaw. 
Instrument
The following 18 basic measurements were applied in the research, plus height and weight. In 
addition to skeletal and girth measurements (recorded in centimetres - cm) each subject had 
his/her age (years), weight (kg), height (cm) and gender recorded. Thus, 20 body dimensions 
were measured, namely:
–  body height 
– body mass
– upper extremity length (a-da
III
) – average of right and left lengths)
– lower extremity length (B-sy) – from pubic symphysis to base 

68 Differentiation and sexual dimorphism due to practising swimming Kinesiologia Slovenica, 11, 1, 65–78 (2005) 
– thigh (maximum) circumference
– calf (maximum) circumference
– arm (maximum) circumference (biceps circumference, flexed)
– forearm (maximum) circumference (extended, palm up)
– chest circumference at rest – nipple line in males and just above breast tissue in females
–  chest circumference after inspiration –  nipple line in males and just above breast tissue in 
females
–  chest circumference after expiration – nipple line in males and just above breast tissue in 
females
– waist circumference 
– hip circumference 
– shoulder width – diameter (a-a)
– hip width – biiliocristal diameter (ic-ic)
– chest width (thl-thl)
– chest depth – antero-posterior chest (xi-xi)
The obtained values were used to calculate anthropometric index, namely: 
Rohrer index = 
 
body mass (g)   
× 100
  
(body height)
3
 (cm)
 
BMI index = 
 
body mass (kg)   
× 100
  
(body height)
2
 (m) 
Marty index = 
 
chest girth (cm)   
× 100
  
(body height) (m) 
Procedure
The body parameters were measured by the method of Martin and Saller. A statistical analysis 
of the collected data was carried out. The age groups of children were merged so as to increase 
the number of observations, which enabled the use of proper statistical methods. According 
to the principles, data were normalised with respect to mean and standard deviation for the 
appropriate age group.
In this way, the influence of age on different body builds was ruled out and thus the older and 
the younger groups of children were merged. 
The following formula was used (Stanisz, 1998): 
Z = 
X
i 
-
 
     
SD
Z – normalised value; 
X
i
 – value of measured parameter (for the child);
– mean value of parameter in the age group of child;
SD – standard deviation of parameter in the age group of child. 

Differentiation and sexual dimorphism due to practising swimming 69 Kinesiologia Slovenica, 11, 1, 65–78 (2005)
The basic statistical parameters such as arithmetic mean, standard deviation, minimal and maxi-
mal values of body dimensions were calculated. T o assess statistical significance of the differences 
between the swimming and non-swimming pupils and to evaluate sexual dimorphism, ANOV A 
(one-way) was applied. The result of ANOV A was a significant value, therefore, F-test was used 
to estimate the differences compared to other values resulting from the tests used in post-hoc 
test groups. Of course, one could carry out a series of tests to compare all possible pairs of mean 
values, but such a procedure would be loaded with incidental effects (randomness). In most 
cases the number of significant differences would be overestimated. The t-test for independent 
samples is used to establish significance of the differences between two samples, while post-hoc 
comparisons include more than 2 samples. 
RESULTS 
Height and body mass are the basic and most representative somatic measures for assessing 
m o r p h o l o g i c a l d e v e l o p m e n t . A l t h o u g h t h e a b o v e p a r a m e t e r s d e s c r i b e w e l l b o d y b u i l d , t h e y d o n o t 
give full information on somatic development. Hence, to complete the basic body dimensions of 
the population under research, other parameters connected with body build as width, height and 
girth were discussed. T o determine the build proportions on the basis of height and body mass the 
Rohrer index was calculated, and on the basis of chest girth the Marty index was calculated. 
Statistical characteristics of normalised measured parameters are shown in Table 1 and 2. 
Table 1: Normalised values of somatic parameters of swimming boys (A) and non-swimming 
boys (B)
AB
MS DM i nM a xMS DM i nM a x
body height 0.04 0.93 -1.68 2.30 -0.11 1.12 -2.04 1.94
body mass -0.12 0.86 -1.57 1.94 0.41 1.28 -1.57 3.88
Rohrer index -0.23 0.77 -2.03 1.27 0.74 1.16 -1.26 3.50
BMI index -0.20 0.79 -1.64 1.24 0.65 1.22 -1.20 3.46
upper limb (arm) length 0.31 1.19 -1.59 4.05 -0.15 1.02 -2.04 2.02
lower limb (leg) length -0.02 1.01 -1.98 2.69 -0.05 1.12 -2.17 2.99
thigh girth 0.01 0.85 -1.36 2.04 -0.05 1.19 -2.08 4.01
calf girth -0.28 0.81 -3.10 1.22 0.58 1.29 -1.48 3.65
arm girth 0.21 0.98 -2.46 2.23 0.22 1.20 -2.12 3.10
forearm girth 0.22 1.03 -1.92 2.35 0.26 1.14 -1.92 2.59
chest girth at rest 0.04 0.82 -1.46 1.96 0.15 1.39 -1.85 2.88
chest girth after inspiration 0.03 0.81 -1.14 2.32 0.29 1.38 -1.81 2.71
chest girth after expiration 0.05 0.86 -1.63 2.10 0.14 1.35 -1.89 3.03
waist girth 0.04 0.70 -1.28 1.37 0.55 1.39 -1.16 3.65
hip girth -0.21 0.71 -1.35 1.06 0.23 1.30 -1.66 3.66
shoulder width 0.18 1.14 -1.77 3.31 -0.10 0.98 -2.49 1.50
hip width 0.20 0.81 -1.24 2.20 -0.07 1.00 -1.67 3.06
chest width 0.08 1.20 -1.78 4.09 0.17 1.14 -1.33 2.96
chest depth -0.38 1.13 -2.09 2.21 0.52 0.80 -0.44 2.04
Marty index 0.02 0.86 -1.63 1.64 0.23 1.29 -1.65 3.81

70 Differentiation and sexual dimorphism due to practising swimming Kinesiologia Slovenica, 11, 1, 65–78 (2005) 
Table 2: Normalised values of the somatic parameters of swimming girls (A) and non-swimming 
girls (B)
AB
MS DM i nM a xMS DM i nM a x
body height 0.07 0.97 -1.44 2.91 0.00 1.00 -2.04 2.42
body mass -0.12 0.87 -1.62 1.84 -0.17 0.85 -1.57 2.10
Rohrer index -0.25 0.84 -1.69 1.98 -0.26 0.84 -1.58 2.35
BMI index -0.21 0.85 -1.54 2.13 -0.24 0.82 -1.47 2.49
upper extremity length 0.05 0.91 -1.59 2.02 -0.21 0.79 -2.04 1.79
lower extremity length l 0.01 1.01 -3.17 2.39 0.06 0.89 -1.98 2.19
thigh girth 0.34 0.92 -1.09 2.22 -0.31 0.94 -2.44 1.86
calf girth -0.23 0.74 -1.61 1.49 -0.06 0.86 -1.48 1.49
arm girth -0.13 0.89 -1.77 1.71 -0.30 0.83 -2.12 1.71
forearm girth -0.12 0.89 -1.68 1.64 -0.36 0.81 -1.68 1.16
chest girth at rest -0.14 0.75 -1.85 1.30 -0.05 0.93 -1.72 2.61
chest girth after inspiration -0.21 0.71 -1.54 1.25 -0.11 0.94 -1.54 2.45
chest girth after expiration -0.14 0.77 -1.76 1.56 -0.06 0.94 -1.63 2.76
waist girth -0.19 0.61 -1.40 1.31 -0.40 0.87 -1.52 2.45
hip girth 0.00 0.90 -1.54 2.17 -0.02 0.98 -1.41 2.42
shoulder width 0.11 0.92 -1.40 2.22 -0.18 0.94 -1.77 2.22
hip width 0.17 1.11 -1.67 2.63 -0.30 1.00 -2.10 2.20
chest width -0.12 0.76 -1.78 1.38 -0.14 0.83 -1.78 2.29
chest depth -0.44 1.04 -1.76 1.22 0.30 0.61 -1.10 1.88
Marty index -0.19 0.88 -2.32 2.14 -0.06 0.89 -1.48 2.69
Body mass, Rohrer index, extremities girths, waist girth and chest depth belong to the most 
diagnostic measures which differentiate between the test groups. This was confirmed by the 
results of the variance analysis, as shown in Table 3. However, in individual parameters, direc-
tions of the influence of swimming training differ by age. 
Differences between the groups of children in terms of body mass and Rohrer index are similar 
in character. Non-swimming boys have the highest level of body mass development. They are 
the heaviest group in terms of Rohrer index, too (Figure 1). They differ statistically significantly 
from their swimming peers and both groups of girls (swimming and non-swimming) (NIR test; 
see Table 4). At the same time, normalised values of both parameters are above the mean value 
for age groups. Non-swimming girls have the lowest body mass and are also the slenderest. It 
is ev ident t hat g i rls w it hout i ncrea sed dose of movement shou ld be heav ier. We considered t he 
fac t t hat body ma ss is cha rac ter ised by su scept ibi l it y to la rger relat ive fluc t uat ions i n st a nd a rd 
l i m it s (B ogd a now icz , 1962). B ody ma s s a lso tend s to decrea se or i ncrea se t he development rate 
in individual phases of ontogenesis. Bochenska (1958) has observed the above phenomenon 

Differentiation and sexual dimorphism due to practising swimming 71 Kinesiologia Slovenica, 11, 1, 65–78 (2005)
and named it “swinging” stage (body height increment) and “fulling” stage (compensate body 
ma ss i ncrement). It is cha rac ter ised by pha sic cha nges i n body ma ss a nd heig ht i ncrement rate 
(deceleration of mass body development accompany acceleration of value jump period and 
vice versa) in the puberty. Perhaps this can explain the observed facts. A lack of statistically 
significant differences between groups in terms of body height indicates that the girls enter the 
phase of puberty and become higher than 11-12 year old boys – their peers. This is confirmed 
by slightly higher values of normalised body height in both groups of girls compared to those 
of boys. At that period development of girls’ body mass decelerates while that of boys’ body 
mass still accelerates. It appears that greater doses of movement (i.e. in the form of systematic 
training) can make great differences in the basic somatic parameters and especially body mass. 
The peculiarity of the swimming training lies in the fact that aerobic metabolism is a source of 
energy for effort. Substratum is a fatty tissue that burns during longer efforts. One might say 
that training reduces boys’ fatty tissue and closes-up training groups to both girl groups. Height 
and body mass proportions are reflected in Rohrer index. 
 Figure 1. The mean values of normalised body mass and Rohrer index.


72 Differentiation and sexual dimorphism due to practising swimming Kinesiologia Slovenica, 11, 1, 65–78 (2005) 
Table 3: ANOVA results (between all groups)
Fp
body height 0.25 0.86
body mass 3.18 0.03
Rohrer index 11.69 0.00
BMI index 8.69 0.00
upper extremity length 2.21 0.09
lower extremity length 0.09 0.96
thigh girth 2.97 0.03
calf girth 7.06 0.00
arm girth 2.77 0.04
forearm girth 3.67 0.01
chest girth at rest 0.60 0.62
chest girth after inspiration 1.89 0.13
chest girth after expiration 0.60 0.61
waist girth 7.56 0.00
hip girth 1.30 0.28
shoulder width 1.18 0.32
hip width 2.21 0.09
chest width 0.91 0.44
chest depth 11.06 0.00
Marty index 1.28 0.28
Table 4: Post-hoc Tukey tests for body mass and Rohrer index
group swimming boys non-swimming boys swimming girls
body mass
non-swimming boys 0.02
swimming girls 0.98 0.02
non-swimming girls 0.81 0.01 0.79
Rohrer index
non-swimming boys 0.00
swimming girls 0.93 0.00
non-swimming girls 0.89 0.00 0.96
BMI index
non-swimming boys 0.00
swimming girls 0.97 0.00
non-swimming girls 0.83 0.00 0.87

Differentiation and sexual dimorphism due to practising swimming 73 Kinesiologia Slovenica, 11, 1, 65–78 (2005)
Th e t r e n d s o f d i ff e r e n c e s b e t we e n t h e g r ou p s i n t e r m s o f e x t r e m i t i e s ’ g i r t h s a r e s e e n i n s h ou l d e r s 
and in legs (see Figure 2). Shoulders differ the same as in the case of arm and forearm girths. 
The group which significantly statistically differed from others was the group of non-swimming 
girls (see Table 5). They had smallest girths and their normalised values were below their age 
group’s mean. Similarly, normalised values of the arm and forearm girths of the swimming 
girls were below the mean value of the groups of non-swimming and swimming boys. However, 
these differences had no statistical significance. In boys from both groups significant differ-
ences were found in shoulder girths. All of the above facts indicate sexual dimorphism of the 
above parameters which are higher in boys. A lack of significant diversity in the swimming 
girls indicates that swimming training stimulates a development of upper-extremity muscles, 
resulting in weakness of dimorphism, when the girl takes up increased motion activity. A lack 
of significant diversity among the boys indicates that the natural developmental processes of the 
boys at this age are so strong that an increase in the dose of movement does not cause an increase 
in muscle mass. Furthermore, it cannot preclude the unaided training of boys from the control 
group in disorganized way, which would annihilate the influence of swim trainings on a natural 
penchant for spontaneous motion activity. 
 Figure 2. The mean values of normalised extremities’ girths


74 Differentiation and sexual dimorphism due to practising swimming Kinesiologia Slovenica, 11, 1, 65–78 (2005) 
The diversity of thigh and calf circumferences proceeds quite differently. Maybe these body 
measures react differently during training. The swimming girls had the highest normalised mean 
value of thigh circumference, although the differences are not statistically significant compared 
to both groups of boys (see Table 5). This mean value is the lowest in the non-swimming girls. 
They differ statistically significantly only compared to swimming girls. 
Table 5: Post-hoc Tukey tests for extremities girths
group swimming boys non-swimming boys swimming girls
thigh girth
non-swimming boys 0.81
swimming girls 0.13 0.08
non-swimming girls 0.15 0.24 0.00
calf girth
non-swimming boys 0.00
swimming girls 0.81 0.00
non-swimming girls 0.29 0.00 0.42
arm girth
non-swimming boys 0.94
swimming girls 0.13 0.11
non-swimming girls 0.02 0.02 0.44
forearm girth 
non-swimming boys 0.87
swimming girls 0.12 0.09
non-swimming girls 0.01 0.00 0.26
A s re ga rd s c a l f g i r t h , t he g roup of non- s w i m m i ng b oy s w a s t he on ly g roup d i ffer i ng s t at i s t ic a l ly 
significantly from others. Their calf circumference was higher. The above observations are quite 
interesting, although it is difficult to unambiguously explain the differences in both girths of 
lower legs. 
Practising of swimming flattens sexual dimorphism of children’s waist girth, but does not dif-
ferentiate between the groups of girls. There are no statistically significant differences in terms 
of development level between the groups of swimming men and swimming women and neither 
between both groups of women (see Table 6). As regards age groups, the normalised parameters 
of both groups of boys lie above the mean value, while those of both groups of girls lie below the 
mean value (see Figure 3). Perhaps, age-dependent are decreasing of girls’ waist girths (associated 
with body mass) and increasing of boys’ waist girths unless they practice swimming, which 
makes them look slimmer and brings the swimming boys closer to girls. 
Training of swimming has the most unidirectional influence on chest depth. This parameter is 
subject to training to a greater extent than others and shows low dimorphism, which was proven 
by the trends in inter-group differences (see Figure 3). 

Differentiation and sexual dimorphism due to practising swimming 75 Kinesiologia Slovenica, 11, 1, 65–78 (2005)
 Figure 3. The mean values of normalised waist circumferences and chest depth
 Bot h sw i m m i ng g roups a re ma rked by h ig her va lues of chest dept h wh i le bot h non-sw i m m i ng 
groups have had lower values in this parameter. Moreover, differences between the swimming 
and the non-swimming groups were statistically significant. Differences between boys and girls 
within both groups were not noticed until the subjects took a swim (see Table 6). We may assume 
that chest depth is more environmentally (susceptible to training) than genotypically (lack of 
gender differences) conditioned. 
Table 6: Post-hoc Tukey tests for waist girth and chest depth.
group swimming boys non-swimming boys swimming girls
waist girth
non-swimming boys 0.02
swimming girls 0.29 0.00
non-swimming girls 0.04 0.00 0.31
chest depth
non-swimming boys 0.00
swimming girls 0.76 0.00
non-swimming girls 0.00 0.27 0.00

76 Differentiation and sexual dimorphism due to practising swimming Kinesiologia Slovenica, 11, 1, 65–78 (2005) 
DISSCUSSION
The beneficial effect of increased dose of movement on physical development of children has 
already been discussed many times, especially highlighting swimming as an activity which is 
particularly stimulating (Dziedziczak & Witkowski, 1998; Leone, Lariviere, & Comtois, 2002). 
Nevertheless, if the movement dose is not suitable for a given level of development as well as 
somatic and motor abilities of the child, unfavourable reactions occur. At the same time the issue 
of how to correctly select children and youth for professional athletics is still dealt with by many 
researches (Bartkowiak, 1997; Laska-Mierzejewska, Piechaczek, & Skibinska, 1985; Piechaczek, 
Lewandowska, & Orlicz, 1995). 
Body build features are important factors determining sport success and one of the elements to 
be taken into account in selection. Many authors point to generally higher values of height and 
body mass in swimming children compared to their non-swimming peers (Bartkowiak, 1978; 
Benefice, Mercier, Guerin, & Prefaut, 1990; Dziedziczak & Witkowski, 1998; Malina, Meleski, & 
Shoup, 1982; Piechaczek, Lewandowska, & Chorzweski, 2000; Skibinska, Laska-Mierzejewska, 
& Piechaczek, 1988; Thorland, Johnson, Housh, & Refsell, 1983). Our research results differ only 
slightly from the results of the cited authors. Although the mean values of the swimming children 
in terms of normalised body height (both girls and boys) are higher than those of the control 
group, the differences are not statistically significant. Hence, in our analysis we have omitted this 
parameter, concentrating only on those traits that have unambiguously differentiated between all 
of the researched groups. In the opinion of many authors, body height is a trait which is not useful 
for selection in the sport of swimming (Skibinska et al., 1988; Wieczorek & Witkowski, 1992). 
In view of the mark direction and the research results found in the literature, it may be assumed 
that a larger sample could deepen the observed phenomenon. A different observation from those 
of other authors is that, in terms of body mass trends, non-swimming boys have advantage 
over swimming-boys. They were statistically significantly heavier than all other groups. In the 
studies of other authors the contrary trend was observed, although Dziedziaczak and Witkowski 
(1998), in addition to age also point to equalising of body mass between boys doing sport and 
those not doing sport. This phenomenon has been explained by an increase in the training load 
and thereby higher movement activity of swimmers. Perhaps this fact has influenced proper 
study results. Rohrer index behaviour is similar to height and body mass. Although it was not 
possible to estimate differences in skin fold tissue between groups of children because no data 
are available, it is most probable that children practising swimming had less fatty tissue than 
non-swimming children. Reduction of fatty tissue during sport training is described in many 
articles (Lowensteyn, Signorile, & Giltz, 1994; Trappe & Pearson, 1994). We could only compare 
BMI. The differences between groups were similar to Rohrer index.
The trends in body girths – especially of the upper extremities – concurred with those observed 
by other authors. In own studies no statistically significant differences among the groups were 
observed, with the exception of swimming girls. It may be assumed that swimming can stimulate 
development of extremities’ muscles in women, but it is not the prevailing development factor 
in boys. Hence, there is lack of significant differences between the swimming girls and both 
groups of boys. 
According to the expectations and in the light of the study results of other authors, differences 
were seen in waist girth and chest depth (Benefice et al., 1990). In swimming children lower 
values of waist circumferences were observed, compared to their non-swimming peers. Their 

Differentiation and sexual dimorphism due to practising swimming 77 Kinesiologia Slovenica, 11, 1, 65–78 (2005)
body shapes in a typical silhouette of a swimmer, which should be marked by streamline shapes. 
Baxter-Jones and colleagues (1995) observed development of the chest and muscles girths during 
swimming training. 
There are several conclusions that can be drawn from the results: 
1.  The methodological approach to the subject of the study enables division of parameters which 
are affected by swimming training and depend on gender. Body mass, limb and waist girths 
and chest depth belong to the most diagnostic features. 
2.  The magnitude of the upper limb circumferences seems to be associated mainly with gender 
which is indicated by lack of significant differences between training and non-training groups 
but significant differences between boys and girls. 
3.  In contrast to the above, it seems that chest size more strongly depends on swimming practis-
ing. 
4.  The established differences between the groups of swimming and non-swimming children 
partially overlap with other authors’ observations. However, this observation does not concern 
the basic somatic traits such as height and body mass. 
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