Effects of backpack-induced fatigue on gait ground reaction force characteristics in primary school children with flat-foot deformity

This study aimed to assess the effects of backpack carriage in different weights and muscle fatigue on the GRF components in primary school children with flat-foot deformity. The GRF components from 42 primary school children (21 with low arch, and 21 with normal) were collected before and after backpack-induced fatigue protocol during shod walking with backpacks in weight 7.5, 10, 12.5 and 15% of the child's bodyweight. The amplitudes of Fx2 of 10%BW and Fz3 of 7.5%BW in the flatfeet group were less than in the healthy group without fatigued condition. (P < 0.05). After fatiguing, the amplitudes of Fx2 of 7.5%BW, Fz3 of 12.5 and 15%BW were significantly decreased in the low arch group than those in the healthy subjects (P < 0.05). Within-group comparisons of measured Fx2 of 10%BW, Fy1 (7.5,10 and 15%BW), Fy2 of 7.5%BW, FZ1 (7.5,10 and 15%BW), FZ2 (7.5,10 and 15%BW), and TTP of TFz1 of 7.5%BW, TFz3 (7.5,10 and 12.5%BW), Loading rate (7.5,10 and 15%BW) were significantly different from pre- to post-fatigue in the flatfeet group(P < 0.05). Within-group comparisons of measured Fy1 of 10%BW, Fy2 (7.5% and 10%BW), FZ1 (7.5% and 10%BW), FZ2 (7.5% and 10%BW), and TTP of TFz3 of 7.5%BW, Loading rate (7.5% and 10%BW) were significantly different from pre- to post-fatigue in the healthy group (P < 0.05). It seems that TTP of GRF variables does have clinical importance for rehabilitation of flatfeet deformity. Carrying heavy backpacks and backpack-induced fatigue had different effects on GRF characteristics among children with low and normal foot arch.