2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
THE RELATIONSHIP BETWEEN PHYSICAL ACTIVITY AND THE
DEVELOPMENT OF BACK MUSCLES SYMMETRY IN CHILDREN
Joca Zurc
Institute for Kinesiology Research, Science and Research Centre of Koper, University of
Primorska, Koper, Slovenia
Contact person: joca.zurc@zrs-kp.si
INTRODUCTION
There are many reasons for the development of bad body posture in children. During the
growth period every functional disturbance, which is strong enough and lasts sufficiently long
may lead to structural changes in spine position. Bad posture does not involve injuries to the
bone or neuromuscular system, but has its origins in insufficient or inappropriate muscular
activity. The most critical period for bad body posture development is during late childhood
(Aaras et al., 1997; Straker et al., 2002. Concomitant with the start of schooling is an increase
in the time spent in a seated position, and a decrease in time spent physical ly active.
Decreased physical activity causes muscular fatigue during sitting, which can lead to bad
body postures, or even to structural deformations of the spine (Avikainen et al., 1999;
Nissinen et al., 1993; Vink et al., 1992; Norris, 2000). With increasing years of schooling, bad
body postures and deformations of the spine also increase.
For elementary school children, the time spent doing homework and in school, is apparently
two or more hours longer than that suggested to be suitable for their stage of development
(Brettschneider, 2000; Laakso et al., 2000). Analysis of postures of 12 year old students
during lessons, conducted with the OWAS (Ovaco working postures analyzing system)
method showed that certain patterns of inadequate posture appear more frequently during the
fourth period compared with the first (Vodnjov, 1990). They are noticeable even earlier, if the
child sits for a long time at an anatomically inappropriate desk and chair. In such cases there
may exist an unbalanced burden between the dominant and non-dominant muscles erector
spinae (m. erector spinae), which causes the curvature of the spine (Aaras et al., 1997;
Straker, Briggs & Greig, 2002).
The present study analysed the relationship between physical activity and symmetry of m.
erector spinae in ten-year-old children. We were also interested in the contribution of
physical activity to the symmetry between dominant and non-dominant m. erector spinae.
METHODS
A total of 222 children (47.7 % girls, 52.3 % boys) participated in the study. There average
(SD) age was 10.5 (6) months. The characteristics of their physical activity (frequency, type
and content) were obtained through two questionnaires, one completed by the children, and
the other by their parents. Characteristics of both m. erector spinae (dominant and nondominant
as regards the hand) were measured with tensiomiography (TMG), an innovative,
non-invasive measuring method (Dahmane et al., 2001; Pišot et al., 2006). Characteristics of
m. erector spinae were studied with five measured tensiomiographic parameters: delay time
(Td), contraction time (Tc), maximum muscle belly displacement (Dm), sustain time (Ts), and
relaxation time (Tr). Due to the large variability and uneven distribution of data, Ts and Tr
were excluded from further analyses. We calculated the index of the direction of asymmetry
(value of dominant m. erector spinae divided by value of non-dominant m. erector spinae)
and an index of the level of asymmetry. The data obtained was then analysed with chosen
univariate and multivariate statistical methods.
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