# Morphological Influences and Energetic Walking Flexibility in Determining Preferred vs. Optimal Speeds: An Evolutionary Human Ecology Perspective on Children and Adolescents

## TL;DR

This study finds that preferred and optimal walking speeds differ in children and adolescents, with body shape and flexibility playing key roles.

## Contribution

The study reveals that optimal and preferred walking speeds are not the same in children and adolescents, unlike in adults.

## Key findings

- Preferred and optimal walking speeds differ significantly in children and adolescents.
- Femur length and hip width influence optimal and preferred walking speeds.
- Lower energy expenditure variability allows for more flexible walking speeds in children.

## Abstract

Locomotion is fundamental to the survival of our species. The most comfortable walking speed may be the most efficient for allocating conserved energy for other functions. However, whether preferred (PLS) and optimal (OLS) speeds align in children and adolescents remains unclear. This study aimed to determine whether OLS and PLS are similar in children and adolescents and how anthropometry influences both speeds and their differences.

Eleven females and 17 males (8–17 years of age) were anthropometrically characterized. Five treadmill walking pace tests were used to identify the OLS and U‐shaped relationship between energy expenditure and speed (χ
2 CoT), indicating walking flexibility. Additionally, PLS was self‐selected using the same protocol. Differences between OLS and PLS were calculated (mean difference [MD]).

No significant sex differences in anthropometry and speed‐related variables were found. OLS, PLS, and their MD in the pooled sample were 3.05 ± 0.13, 2.46 ± 0.51, and 0.60 ± 0.46, respectively, with significant differences between OLS and PLS (p < 0.0001). Femur length (FL), Bi‐iliac breadth (BIL), and χ
2 CoT explained variance in OLS, PLS, and MD, respectively, in the forward stepwise regression models.

Unlike adults, OLS and PLS are not interchangeable in children and adolescents. Participants with lower χ
2 CoT (greater flexibility) can select comfortable speeds farther from OLS without energetic penalty. Taller individuals with longer femurs and wider hips might have biomechanical advantages in reaching higher OLS and PLS, but this reduces flexibility. These traits, along with the growth and development pattern of
Homo sapiens
, may reflect evolutionary advantages relevant to interspecies competition.