Table 2.

Mean, standard deviation and p-value of backpack and total load by school-grade in absolute values and after normalizing for body weight

	Backpack		Total load
	load (kg)	load·BW−1	load (kg)	load·BW−1
Load (mean)
5th year	4.99 (1.42)	0.130 (0.044)	5.40 (1.54)	0.140 (0.048)
9th year	4.06 (1.21)	0.078 (0.027)	4.41 (1.44)	0.085 (0.032)
p	< 0.001	< 0.001	< 0.001	< 0.001
Max subject’s load (mean)
5th year	6.25 (1.30)	0.160 (0.047)	6.83 (1.30)	0.177 (0.052)
9th year	5.13 (1.13)	0.098 (0.029)	5.69 (1.36)	0.111 (0.034)
p	< 0.001	< 0.001	< 0.001	< 0.001