Multilevel modelling of somatotype components: the Portuguese sibling study on growth, fitness, lifestyle and health.
BACKGROUND
Somatotype is a complex trait influenced by different genetic and environmental factors as well as by other covariates whose effects are still unclear.


OBJECTIVE
To (1) estimate siblings' resemblance in their general somatotype; (2) identify sib-pair (brother-brother (BB), sister-sister (SS), brother-sister (BS)) similarities in individual somatotype components; (3) examine the degree to which between and within variances differ among sib-ships; and (4) investigate the effects of physical activity (PA) and family socioeconomic status (SES) on these relationships.


METHODS
The sample comprises 1058 Portuguese siblings (538 females) aged 9-20 years. Somatotype was calculated using the Health-Carter method, while PA and SES information was obtained by questionnaire. Multi-level modelling was done in SuperMix software.


RESULTS
Older subjects showed the lowest values for endomorphy and mesomorphy, but the highest values for ectomorphy; and more physically active subjects showed the highest values for mesomorphy. In general, the familiality of somatotype was moderate (ρ = 0.35). Same-sex siblings had the strongest resemblance (endomorphy: ρSS> ρBB> ρBS; mesomorphy: ρBB= ρSS> ρBS; ectomorphy: ρBB> ρSS> ρBS). For the ectomorphy and mesomorphy components, BS pairs showed the highest between sib-ship variance, but the lowest within sib-ship variance; while for endomorphy BS showed the lowest between and within sib-ship variances.


CONCLUSIONS
These results highlight the significant familial effects on somatotype and the complexity of the role of familial resemblance in explaining variance in somatotypes.
a CIFI2D, Faculty of Sport, University of Porto , Porto , Portugal.
Sara
S
Pereira
b Pennington Biomedical Research Center, Louisiana State University , Baton Rouge , LA , USA.
Peter T
PT
Katzmarzyk
a CIFI2D, Faculty of Sport, University of Porto , Porto , Portugal.
Thayse Natacha
TN
Gomes
c Federal University of Santa Catarina , Florianópolis , Santa Catarina , Brazil.
Michele
M
Souza
d Federal University of Technology-Paraná (UTFPR) , Campus Curitiba , Curitiba , Brazil.
Raquel N
RN
Chaves
e Department of Physical Education , Federal University of Viçosa , Viçosa , Minas Gerais , Brazil.
Fernanda K Dos
FKD
Santos
a CIFI2D, Faculty of Sport, University of Porto , Porto , Portugal.
Daniel
D
Santos
f Department of Public Health Sciences , University of Chicago , Chicago , IL , USA.
Donald
D
Hedeker
a CIFI2D, Faculty of Sport, University of Porto , Porto , Portugal.
José A R
JAR
Maia
D000293:Adolescent; D002648:Child; D015444:Exercise; D005190:Family; D005260:Female; D006128:Growth; D006262:Health; D006801:Humans; D008019:Life Style; D008297:Male; D008962:Models, Theoretical; D010809:Physical Fitness; D011174:Portugal; D035781:Siblings; D012923:Social Class; D013008:Somatotypes / Q000502:physiology*; D055815:Young Adult
Similarity; children; physical activity; physique; youth