Physical fitness spurts in pre-adolescent boys and girls: Timing, intensity and sequencing.

We aim to (1) estimate age of attainment of the peak mid-growth spurt in stature (age-at-peak MGS) in pre-adolescent boys and girls; (2) identify the timing, intensity, and sequences of physical fitness (PF) spurts aligned by the age-at-peak MGS; and (3) identify any sex differences in PF spurts aligned by age-at-peak MGS. The sample included 180 Portuguese children (90 girls) aged 6 to 10 years at study entry who were followed annually for 4 years. Height, health-, and performance-related PF were assessed. Age-at-peak MGS and PF spurts were estimated using a non-smooth mathematical procedure. Boys' and girls' age-at-peak MGS occurred at 7.8 ± 0.47 years and 8.0 ± 0.72 years, respectively. PF spurts' timing aligned by age-at-peak MGS were as follows: (1) before age-at-peak MGS: