Acute effects of footwear on running impact loading in the preschool years.

The aim of this study was to assess acute effects of footwear conditions (barefoot, minimalist and standard running shoes) on running impact loading in the preschool years. Fourty-eight habitually shod preschool children (26 males and 22 females) were divided into four age groups (3-, 4-, 5- and 6-year-old). Children performed a simple running game in three different conditions. Three-dimensional biomechanical analysis was carried out during overground running. Statistical parametric mapping was performed on the vertical ground reaction force profiles during the stance phase and one-way repeated measures ANOVA on the vertical instantaneous loading rate. Three-year-old children displayed significantly lower vertical ground reaction force values in the barefoot condition compared to minimalist (3-7% stance) and standard running shoes (7-11% stance). There were also differences in vertical instantaneous loading rate, where 3-year-olds had lower loading when barefoot than in minimalist (p = 0.010, d = 1.19) or running shoes (p = 0.045, d = 0.98), despite no differences in the footstrike pattern (mostly rearfoot-midfoot strike). No differences were found for the older children. Running in minimalist shoes did not imitate barefoot running in 3-year-old children. On the contrary, increased loading was observed in minimalist shoes in early running developmental stages.