Table 1 Modelling of reduction in BMI for a single 'average' individual new to active transport (Effects are averaged over one calendar year)
From: Cost-effectiveness of active transport for primary school children - Walking School Bus program
| Â | Prep to Grade 2 | Comments | |
|---|---|---|---|
| Â | Boys | Girls | Â |
Height (m) | 1.20 | 1.19 | Mean height for 5-7 year age group [19] |
Weight (kg) | 23.50 | 23.48 | Mean weight for 5-7 year age group [19] |
Body mass index BMI (kg/m2) | 16.24 | 16.47 | Mean BMI for 5-7 year age group [19] |
Estimated total energy expenditure (MJ/day) | 6.43 | 6.64 | Total energy expenditure (MJ/day) = [.107 × weight (kg)] + [2.91 × height (metres)] + .417 [20] |
Estimated total energy expenditure (kJ/day) | 6433 | 6404 | Conversion to kilojoules - multiply by 1000 |
Increased METS -- walking versus sitting | 2.5 | 2.5 | Metabolic equivalents for sitting = 1.0, walking 3.5. Therefore, additional energy expenditure of active transport to school = 2.5 METS [13] |
Extra time spent on walking to and from school (min) | 28.30 | 28.30 | Mean travel time for Victorian children participating both in morning and afternoon WSB [15] |
Energy expenditure increase from WSB participation(kJ per day) | 116 | 116 | Increase in individual energy expenditure from walking (kJ/school day) = weight (kg) × increased METs × time (hrs) × factor to convert kcal to kJ (4.2) |
Average number of days of WSB participation to and from school per week | 1 | 1 | Based on Victorian WSB experience 2004 [15], where 1,675 enrolled children engaged in 3,049 sessions of active transport per week. This translates to 1.82 sessions per week/child, or about equivalent of walking to and from school one day per week. |
Number of potential weeks of WSB participation per year | 40 | 40 | Number of weeks in the school year. |
Total number of days of WSB participation per year | 40 | 40 | Number of WSB days per week × number of school weeks |
Energy expenditure increase from WSB participation (kJ) | 13 | 13 | Total increase in individual energy expenditure × number of WSB days per year divided by 365 |
Relative increase in energy expenditure with WSB participation (%) | 0.20 | 0.20 | Average individual energy expenditure from WSB as % of estimated total energy expenditure per day: (13/6433) × 100 and (13/6404) ×100 for boys and girls respectively |
Conversion factor | 0.45 | 0.45 | Factor for conversion of relative change in energy balance to relative change in weight [14, 21] |
Relative lower weight with WSB participation (%) | 0.09 | 0.09 | [1-(energy expenditure1/energy expenditure2)0.45]*100 |
Absolute lower weight with WSB participation (kg) | 0.02 | 0.02 | 0.09% of original weight |
New weight (kg) | 23.48 | 23.46 | Original mean weight minus decrease in weight as a result of WSB participation |
New BMI (kg/m2) | 16.23 | 16.45 | New weight divided by square of height |
Reduction in BMI (kg/m2)a | 0.014 | 0.015 | Original BMI minus new BMI for new participants |