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 (P(1), P(2) and P(3)) were created for body weight and physical fitness data composite (PF(composite)). Differences were found between the slopes of P(1) and P(3) 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) (P(1), P(2) and P(3): 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.