This study aimed to analyse the types of relationship between internal and external intensities in fourth grade students (age: 9.4 ± 0.19; height: 1.37 ± 0.187; body mass 41.56 ± 7.95). Fifty-five students in two groups participated in fourteen sessions monitored with wGT3X accelerometers and Polar Team Pro® heart rate monitors. It showed a positive relationship for all variables, with average heart rate significantly related to total distance (r=0.441, p<0.001) and average speed (r=0.346, p<0.001). Maximum heart rate also showed a significant relationship with both total distance and average speed respectively (r=0.329; p<0.001; r=0.183; p<0.001). The use of alternative approaches with small-sided games and the use of playful force such as educational CrossFit exercises may positively promote a related improvement in exercise intensity already at a young age.