Compositional Isotemporal Substitution Analysis of 24-h Movement Behaviours and Speed Capability in Preschoolers

Speed capability is critical for early childhood development, but troubling patterns are emerging in the motor fitness of Chinese preschoolers (3-6 years). This study investigated how compositional 24-h movement behaviours (sleep, sedentary behaviour [SB], light physical activity [LPA] and moderate-to-vigorous physical activity [MVPA]) relate to speed capability.

Via compositional data analysis and isotemporal substitution modelling, we assessed relationships between 24-h movement behaviours (sleep, SB, LPA and MVPA) and speed capability in 275 preschoolers (mean age 4.98 ± 0.76 years). Participants completed 20-m sprint tests and 7-day accelerometry. Time-reallocation effects were quantified through pairwise behavioural substitutions (5- to 30-min durations), with all models adjusted for age, sex and BMI z scores (z-BMI).

Higher relative MVPA time significantly predicted faster sprint times (β = -1.302, p < 0.001), while higher LPA predicted slower times (β = 1.570, p = 0.003). Reallocating 15 min from sleep, SB or LPA to MVPA reduced sprint times by 0.176, 0.201 and 0.385 s, respectively (all p < 0.05). Conversely, reallocating MVPA to other behaviours worsened performance. The effects exhibited asymmetry: displacing time away from MVPA impaired speed capability to a greater extent than equivalent gains in MVPA time improved it.

MVPA is the strongest positive predictor of speed capability in preschoolers. Optimizing 24-h movement patterns by reallocating time from LPA or SB to MVPA is associated with enhanced speed performance, supporting targeted interventions for early childhood development.