Neuromuscular, kinetic and kinematic differences in drop jumping between male adolescents with and without intellectual disability.

BACKGROUND: Individuals with intellectual disability (ID) have lower performance in vertical jumps compared to individuals without ID. Training programmes including drop jump (DJ) exercises to gap this deficit are required. However, there is a lack of knowledge on biomechanical variables may influence DJ performance in young people with ID. RESEARCH QUESTION: Are there differences in the neuromuscular, kinetic and kinematic parameters in DJ between male adolescents with and without ID (WID and NID, respectively). METHODS: Thirteen male adolescents WID (Wisk III intelligence quotient: 55.6 ± 11.2) and thirteen age-matched boys NID executed DJ from 30 cm on a force-plate. The vastus lateralis (VL) and biceps femoris (BF) electromyogram (EMG) as well as the knee kinematics and kinetics were obtained. RESULTS: WID had significantly (p < .05) lower DJ height, knee power, peak angular velocity and stiffness compared to NID. VL activity was higher and BF/VL co-activation was lower in WID than NID. SIGNIFICANCE: The deficit in DJ performance shown in WID was accompanied with lower power and stiffness, as well as lack of coordination in the lower limb muscles. Improving these variables, with specific and targeted training interventions, may diminish the performance gap with their age-matched counterparts.

Biomechanical comparison in different jumping tasks between untrained boys and men.

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.