Samenvatting

Introduction: It has been suggested that physical education (PE) can make a meaningful contribution to children's physical activity (PA) levels. The amount of moderate-to-vigorous physical activity (MVPA) in PE has been quantified in various manners, including heart rate monitoring and direct observation (Fairclough & Stratton, 2005). However, data on the contribution of PE to total PA is scarce, and PE's contribution to total physical activity energy expenditure (PAEE) has to our knowledge never been determined. This is probably explained by the methodological complexity of determining PAEE (Welk, 2002). However, the fairly recent emergence of combined sensing methodology allows for low-invasive measurement of PAEE in free-living conditions. In this paper, we present the first data of an ongoing study using combined heart rate monitoring and accelerometry, together with activity diaries. We assessed the contribution of PE and other school-related activity to PAEE and MVPA.
Methods: Nineteen secondary school students (16 ± 0,7 yrs, BMI 22 ± 4) were included after they and their parents had consented. All had 100 minutes of scheduled PE per week. Actiheart monitors (CamNtech, Cambridge, UK) were used to determine PAEE on four weekdays and two weekend days consecutively. Actiheart monitors combine a heart rate monitor and an uniaxial accelerometer in a single 10 gram unit, that is applied to the chest with electrodes. Using a step test, an individual heart rate-energy expenditure relationship was determinded in each subject. Through a validated branched equation model (Brage, S. et al., 2007), energy expenditure was calculated. In addition, subjects kept an activity diary for the same six-day period. They recorded predefined activities including PE and active transport. These activities were then retraced to the Actiheart data by visual inspection.
Results: Table 1 shows the (contribution of) PE, and school-related active transport to PAEE, while table 2 shows similar data for MVPA. Data are mean (± SD).

Table 1: PAEE for PE, and active transport (AT). Table 2: MVPA for PE and active transport (AT).
PAEE (KJ) % of total % of school
PE 805(474) 5(4) 16(7)
AT 1698(1033) 11(6) 31(11)
MVPA (min) % of total % of school
PE 36(19) 9(8) 22(11)
AT 90(56) 20(11) 48(14)

Over all six days, the physical activity level (PAL, which is total EE/Resting EE) was 1,54 ± 0,12; total MVPA was 472 min ± 179, and total PAEE 16262 KJ ± 5267. PAEE at school (4 days, including AT) was 5311 ± 3065 KJ, amounting to 34 % of total PAEE during the six measurement days. Students accumulated 179 ± 77 minutes of MVPA at school, which was 38% of total MVPA.
Discussion: To our knowledge, this is the first study to present data on PE's contribution to total physical activity energy expenditure. Over the six measurement days, PE contributed 5% to total PAEE, and 16% to school-related PAEE. This was substantially less than the amount of energy expended for active transport to and from school. However, it should be noted that in the Netherlands, the vast majority of secondary school students cycle to school. And while PE was scheduled on one day per week in all of the measured students, active transport takes place on all school days. The total amount of MVPA accumulated at school was 179 minutes. With adolescent physical activity guidelines generally recommending 60 min of MVPA per day, i.e. 420 minutes per week, this means that school-related PA covered ~43% of this. PE provided 36 minutes to this total, all on one day. It could be argued that daily PE could potentially provide a substantial amount of MVPA. But with current time allocated to PE in the curriculum, its contribution to physical activity guidelines and PAEE is quite modest. The preliminary data presented here reflect a small subsample of a larger study that is still in progress. Therefore, care should be taken not to interpret these outcomes as representative for the whole of the Netherlands. However, they do provide a first indication for the order of magnitude of the contribution of PE and school-related activity to total PAEE.
References:
Fairclough, S. J. & Stratton, G. (2005) Physical Activity Levels in Middle and High School Physical Education: A Review. Pediatric Exercise Science, 17, 217.
Welk, G. J. (2002) Physical activity assessments for health-related research, Champaign, Ill.; United States, Human Kinetics.
Brage, S., Ekelund, U., Brage, N. Hennings, M.A., Froberg, K., Franks, P.W., Wareham. N.J. (2007). Hierarchy of individual calibration levels for heart rate and accelerometry to measure physical activity. J Appl Physiol, 103, (682-692)