Heart Rate Kinetics Response of Pre-Pubertal Children during the Yo-Yo Intermittent Endurance Test-Level 1

This study analyzed heart rate (HR) kinetics during the Yo-Yo Intermittent Endurance Test-level 1 (Yo-Yo IE1) in children. At the middle of the school year, 107 boys (7⁻10 years old) performed the Yo-Yo IE1. Individual HR curves during the Yo-Yo IE1 were analyzed to detect an inflection point between an initial phase of fast rise in HR, and a second phase in which the rise of HR is slower. The 7^th shuttle of the test was established as the inflection point. Engagement with extra-school sports practice was identified. Percentile groups (P₁, P₂ and P₃) were created for body weight and physical fitness data composite (PF_composite). Differences were found between the slopes of P₁ and P₃ on phase 1 for body weight (12.5 ± 2.7 vs. 13.7 ± 2.0 bpm/shuttle; p = 0.033; d = 0.50) and PF_composite (14.2 ± 2.5 vs. 12.5 ± 2.0 bpm/shuttle; p = 0.015; d = 0.75). Time spent >95% of peak HR was longer for the children engaged with extra-school sports practice (335 ± 158 vs. 234 ± 124 s; p < 0.001; d = 0.71); differences were also detected for PF_composite (P₁, P₂ and P₃: 172 ± 92, 270 ± 109, and 360 ± 157 s, respectively; p < 0.05; d = 0.66⁻1.46). This study indicates that physical fitness and body weight influence HR kinetics during the Yo-Yo IE1 in pre-pubertal boys.