Objectively measured physical activity and longitudinal changes in adolescent body fatness: an observational cohort study.
BACKGROUND
The data regarding prospective associations between physical activity (PA) and adiposity in youth are inconsistent.


OBJECTIVE
The objective of this study was to investigate associations between baseline levels of objectively measured PA and changes in adiposity over 2.5 years from mid-to-late adolescence.


METHODS
This was an observational cohort study in 728 school students (43% boys) from Cambridgeshire, United Kingdom. Fat mass index (FMI, kg m(-2) ) was estimated at baseline (mean ± standard deviation age: 15 ± 0.3 years) and follow-up (17.5 ± 0.3 years) by anthropometry and bioelectrical impedance. Habitual PA was assessed at baseline by ≥3 d combined heart rate and movement sensing. Average daily PA energy expenditure (PAEE) and the time (min d(-1) ) spent in light, moderate and vigorous intensity PA (LPA, MPA and VPA, respectively) was estimated. Multilevel models were used to investigate associations between baseline PA and change in FMI (ΔFMI). Adjustment for baseline age, sex, follow-up duration, area-level socioeconomic status, season of PA assessment, sedentary time, energy intake and sleep duration was made; baseline FMI was also added in a second model.


RESULTS
FMI increased significantly over follow-up (0.6 ± 1.2 kg m(-2) , P < 0.001). Baseline PAEE and LPA positively predicted ΔFMI in overfat participants (P ≤ 0.030), as did VPA in initially normal fat participants (P ≤ 0.044). There were further positive associations between PAEE and ΔFMI in normal fat participants, and between MPA and ΔFMI in both fat groups, when adjusted for baseline FMI (P ≤ 0.024).


CONCLUSIONS
Baseline PAEE and its subcomponents were positively associated with small and unlikely clinically relevant increases in ΔFMI. These counter-intuitive findings may be explained by behavioural changes during the course of study follow-up.
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
P J
PJ
Collings
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
K
K
Wijndaele
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
K
K
Corder
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
K
K
Westgate
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
C L
CL
Ridgway
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
S J
SJ
Sharp
UKCRC Centre for Diet and Activity Research (CEDAR), MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
A J
AJ
Atkin
MRC Human Nutrition Research, University of Cambridge, Cambridge, UK.
A M
AM
Stephen
Developmental Lifecourse Research Group, Department of Psychiatry, University of Cambridge, Cambridge, UK.
D
D
Bamber
Developmental Lifecourse Research Group, Department of Psychiatry, University of Cambridge, Cambridge, UK.
I
I
Goodyer
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
S
S
Brage
MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.|Department of Sport Medicine, Norwegian School of Sports Science, Oslo, Norway.
U
U
Ekelund
D000273:Adipose Tissue; D050154:Adiposity / Q000502:physiology; D000293:Adolescent; D000294:Adolescent Behavior; D015992:Body Mass Index; D002648:Child; D002652:Child Behavior; D002675:Child, Preschool; D002149:Energy Intake; D005260:Female; D006801:Humans; D007899:Leisure Activities; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D011446:Prospective Studies; D057185:Sedentary Behavior; D006113:United Kingdom / Q000453:epidemiology; D015430:Weight Gain / Q000502:physiology
Adiposity; motor activity; prospective study; youth