Predictors of change in children's physical activity: potential targets for intervention

Esther van Sluijs, Chris Craggs, Kirsten Corder, Alison McMinn, Andy Jones, Ulf Ekelund, Simon Griffin

• Physical activity (PA) is important for children’s current and future health*

• Many children do not meet current PA guidelines of 60 minutes moderate-to-vigorous PA each day**

• self-report – 60-70%• accelerometry – 0-99%

• PA declines in late childhood and adolescence***

Physical activity in children

*e.g. Jansen et al, IJBNPA 2010; Telema, Obes Facts 2009; Yang et al, IJO 2009**Ekelund et al, BJSM 2011***e.g. Nader et al, JAMA 2008; Jago et al, AJPM 2008; Corder al et, Ped 2010

• Effects of PA promotion interventions in children have been varied*

• Knowledge about factors associated with PA change will aid intervention development• current data mostly cross-sectional**

• Review of prospective studies*** • only identified 46 studies• few factors studied consistently • predominant use of self- or parent-reported PA

Promoting physical activity

*e.g. Kriemler et al, BJSM 2011; Van Sluijs et al, BJSM 2011**e.g. Sallis et al, MSSE 2000; Van der Horst et al, MSSE 2007**Craggs et al, AJPM 2011

• To study predictors of 1-year change in PA in 10-year old children, using:

• exposure variables at different levels of influence• objectively-measured PA• temporal and intensity-specific outcomes

Objective

• Sport, Physical activity and Eating behaviour, Environmental Determinants in Young people (SPEEDY)

• Population-based sample• N=92 schools across Norfolk• sampled for environmental heterogeneity• invited all Year 5 children (aged 9-10)

• Data collection at baseline (2007)• during 12-week Summer term• questionnaires and anthropometry at school measurement

session• home pack including accelerometer & parent questionnaire

Methods – 1

**

Van Sluijs et al., BMC Publ Health 2008

•Data collection at follow-up (2008)• during 12-week Summer term• accelerometer and questionnaire sent home

•Outcome variables• change in % wear time spent in moderate PA (MPA: 2000-

3999cpm) and vigorous PA (VPA: ≥4000cpm)• separate for weekdays and weekends

•Exposure variables (baseline)

Methods – 2

Methods – exposure variables

Demographic & Biological

5 variables

Psychological

5 variables

Environmental

8 variables

Socio-cultural

9 variables

Behavioural

1 variable

age sexparental education

active travel

self-efficacybarriersPA preference

home in cul-de-sacavailability of parksdistance to green space

family cohesivenessrules and restrictionselectronic equipment

Results – descriptive

0

10

20

30

40

50

60

MPA VPA MPA VPA

Weekday Weekend

Min

ute

s per

day

Baseline

Follow- up

P<0.001

P=0.012

ns

ns

Figure: Minutes spent in MPA and VPA at baseline and 1-year follow-up.

• Both MPA and VPA decreased significantly at weekend days only

•755 children provided valid data (≥3 days of 500 minutes)• 37% of SPEEDY-1 participants (N=2064)• fewer boys and those of lower SES

Results – final models

NOTES: *p<0.05; **p<0.01; ***p<0.001; BMI: body mass index; HHI: Herfindahl-Hirschmann Index

Exposure variables (N considered) Weekdays Weekends MPA VPA MPA VPA

Biological and socio-demographic (5 vars)

- BMI z-score - -0.16*** - -0.29**

- Age parent left full-time education (>16 yrs vs. 16 yrs)

-

-0.22*

-

-

Psychological (5 vars)

- PA preference (yes vs. no) - - 0.40* 0.41*

- Barrier, lack of PA equipment (yes vs. no)

- - -0.54* -

Socio-cultural (9 vars)

- Family logistical support - - 0.15** 0.18** *

- Peer support (high vs. low) - 0.23** - -

- Freedom to play

- - - -0.14*

Behavioural (1 var)

-

Environmental (8 var)

- HHI (land use mix) High 0.49** - 0.04 Med high 0.22 0.12 Low med 0.27 -0.57* Low REF REF

• Multilevel linear regression models

• Models adjusted for baseline PA, sex and school

• No differences by sex

•Predictors of change in PA are time- and intensity-specific• targets for interventions may vary

•Few factors associated with changes on weekday• influence of school-level factors?• less change in PA on weekdays

•Study has many strengths, but also some limitations:• did not assess potential complex associations• differential drop-out• multiple testing

Discussion

•Interventions to prevent declines in PA in primary school children may focus on:

• weekend activity• family logistical support • preventing further declines in those with higher BMI

Conclusion

ACKNOWLEDGEMENTS

Part of this work was undertaken by the Centre for Diet and Activity Research (CEDAR), a UKCRC Public Health Research Centre of Excellence.

The SPEEDY study was funded by the National Prevention Research Initiative and the Medical Research Council.