Words Matter with Age: Instructions Dictate Self-Selected Walking Speed in Young and Older Adults

Background Our previous work demonstrated that in young adults, 61% of gait speed variance was attributable to instruction type. However, no study has investigated whether verbal instructions differentially influence older adults.

This study investigated how walking prompts contribute to gait speed variability across age groups.

Thirty-four young adults (21±2 years) and twenty-eight older adults (70±5 years) performed walking trials responding to 24 different instructions.

Average walking speed was 1.23±0.30 m/s. Between-subject variance accounted for 25.3% of the total variance, while between subject and instruction variance components accounted for 76.1% of the total variance. When analyzed separately, variance due to instructions accounted for similar amounts of total variance within older adults (56.9%) and young adults (55.7%), a statistically non-significant difference (p = 0.85). A significant age-instruction interaction (χ ² =76.84, df = 23. p<0.001) revealed that the age differences between average gait speed depended on which instruction was given. Complex instructions elicited the largest between group differences (β:-0.24 to -0.32 m/s), while simple tasks showed minimal differences (β:-0.03 to -0.06 m/s).

Instructions explain similar variance within each age group (~56%), but the model treating instructions as fixed effects captures how different age groups respond to the same instructions. These findings highlight the critical importance of instruction standardization in gait assessment protocols, as systematic age-related differences in instruction interpretation can significantly impact measured outcomes. Instructions that produce minimal between-group differences may be most appropriate for standardized clinical assessments, while those showing larger age effects may be valuable for detecting age-related changes in gait control.