The effect of family and friend support on physical activity through adolescence: a longitudinal study.
BACKGROUND
This study examined if family and friend support predicted adolescent physical activity (PA) across a five-year time span.


METHODS
The Iowa Bone Development Study collected objective measures of physical activity and self-report of physical activity psychosocial factors at ages 13 (n = 306), 15 (n = 356), and 17 yr (n = 317). Total moderate and vigorous-intensity PA (MVPA) and MVPA after 3 pm on weekdays (MVPA-PM Weekday) were measured using ActiGraph accelerometers. Family Support for PA and Friend Support for PA scales were measured using the Choices questionnaire. Models were adjusted for SES (mother's education) and somatic maturity (Mirwald predictive equations for maturity offset). Spearman correlation coefficients examined tracking of scales at ages 13, 15 and 17. Logistic regression estimated the odds ratio for being in the lowest tertile of each scale at age 17 if in the lowest tertile at age 13. Linear mixed regression models investigated associations between these scales and MVPA outcomes over time.


RESULTS
Two- and five-year intra-variable tracking associations for Family Support and Friend Support scales were moderate (r = 0.32-0.58), except for the comparison between age 13 and age 17 Friend Support for girls, which resulted in a low association (r = 0.26). Boys and girls in the lowest tertile for support at age 13 were more likely to remain in the lowest tertile at age 17 compared to those in the middle and upper tertiles. The regression models indicated that when all other factors were held constant, an increase in family and/or friend support resulted in an increase in both MVPA outcomes


CONCLUSIONS
From early to late adolescence, support for PA from the family and/or support from friends results in higher levels of total and discretionary MVPA. However, the importance of support in predicting MVPA decreased with age.
Kinesiology Department at California State, University-Monterey Bay, University Corp. 117C Seaside, Monterey, 93955, CA, USA. jmorrissey@csumb.edu.
Joanna L
JL
Morrissey
Department of Health and Human Physiology and the Department of Epidemiology at the University of Iowa, 130 Field House, Iowa City, IA 52242, USA. kathleen-janz@uiowa.edu.
Kathleen F
KF
Janz
Department of Epidemiology at the University of Iowa, 5205 Westlawn Building, Iowa City, IA 52242, USA. elena-letuchy@uiowa.edu.
Elena M
EM
Letuchy
Department of Health and Human Physiology at the University of Iowa, E102 Field House, Iowa City, IA 52242, USA. shelby-francis@uiowa.edu.
Shelby L
SL
Francis
Department of Preventive and Community Dentistry and Department of Epidemiology at the University of Iowa, N-328 Dental Science, Iowa City, IA 52242, USA. steven-levy@uiowa.edu.
Steven M
SM
Levy
D000293:Adolescent; D000294:Adolescent Behavior; D000367:Age Factors; D015444:Exercise; D005190:Family; D005260:Female; D033062:Friends; D015438:Health Behavior; D006801:Humans; D007484:Iowa; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D016017:Odds Ratio; D057566:Self Report; D012944:Social Support; D011795:Surveys and Questionnaires