The purpose of the present study was to examine the effect of chronological age and gender on speed development during different sprinting phases in children and adolescents of both genders. The sample consisted of 360 sedentary pupils aged between 7 and 18 years, with 15 pupils representing each subgroup. The 30-m sprint speed was measured with photocells every 10 m. According to the results, boys and girls showed a gradual improvement in running speed during each sprint phase. The 18-year-old boys had significantly higher sprint speed in all measured distances compared to the 15-year-old or younger boys (p < 0.05), whereas the 18-year-old girls had significantly higher speed at the distances of 0 to 10, 10 to 20, 20 to 30, and 0 to 30 m compared to the 13- and 12-year-old or younger girls (p < 0.05). Significant differences between genders in the 15-years-old or older participants were observed. It is concluded that, from 7 to 18 years of age, gender and chronological age are factors that affect running speed during the 30-m sprint. Furthermore, the performance on each sprint phase is uniformly affected by the chronological age. Boys run faster than girls in all running phases, and the span between genders increases after the age of 15 years. It is useful that coaches take these findings into consideration when evaluating children in sprint performance.

The aim of this study was to examine the fatigue and recovery in boys and men during a maximal intermittent isometric fatigue test of the knee extensor muscles, by evaluating the electromyogram of vastus lateralis, vastus medialis and biceps femoris. Thirteen boys (10.0 ± 0.8yrs) and 13 men (26.1 ± 4.2yrs) were fatigued until torque reached 50% of its initial value. Three and 6 min after, a maximal isometric knee extension test was assessed. Men had faster torque decline during fatigue and slower torque recovery compared with boys. Agonist activity declined in both groups during fatigue but men had greater extent of reduction. After 6 min boys recovered fully in respect to agonist EMG, whereas this was not the case for the men. The lower level of fatigue and faster recovery in boys could be attributed to the limited inhibition that was observed in the boys’ agonist muscles, whereas the antagonist activity does not seem to play a role in the fatigue or recovery differences between the groups.

This study examines the biomechanical differences during different vertical jump tasks in 12 prepubescent and 12 adult males. The sagittal knee kinematics, vertical ground reaction force (vGRF) and electromyographic (EMG) activity of 5 lower extremity muscles were recorded. Compared with boys, men presented higher peak vGRF during the propulsive phase in all examined jumps, but lower values during the braking phase, even when related to body mass. Normalized EMG agonist activity in all phases was higher in men (p < .05), while antagonist coactivation was enhanced in boys (p < .05). The knee joint was on average 9 degrees more flexed at touchdown in men during drop jump tasks, but boys exhibited 12 degrees and 17 degrees higher knee flexion at the deepest point when performing drop jump from 20 and 40 cm, respectively. In conclusion, the performance deficit observed in boys in all jump types is a reflection of their immature technique, which could be partly attributed to the less efficient stiffness regulation and activation of their neuromuscular system.

The purpose of this study was to examine central and peripheral factors of fatigability that could explain the differences in fatigability between adults and prepubertal boys after maximal sustained isometric contraction. A total of 11 untrained adult men and 10 prepubescent boys volunteered to participate in this study. The level of voluntary activation was assessed before and after fatigue by means of the twitch interpolation technique as well as peak twitch torque, maximum rate of torque development and maximum M-wave (Mmax) area of the soleus and medial gastrocnemius. The fatigue-inducing protocol consisted of a sustained maximal voluntary contraction (MVC) of the ankle's plantar flexor at 100% of MVC until the task could no longer be sustained at 50% of MVC. During the fatigue-inducing protocol, boys were fatigued less, showing longer endurance limit and delayed torque and agonist EMG decrease. After fatigue, the level of activation decreased to a similar extent in both groups, and boys were less affected regarding their peak twitch torque and rate of torque development, whereas no differentiation between the groups was observed regarding the decrease in Mmax area of the examined muscles. The results obtained provide evidence that the greater fatigability resistance in prepubertal children during sustained maximal contractions is mainly explained by peripheral rather than central factors.