Differences in counter-movement jump between boys with and without intellectual disability

The purpose of this study was to describe the performance and biomechanical parameters of the counter-movement jump for young people with ID, in comparison with age matched individuals without ID. Volunteers with ID (n = 13; age = 15.3 ± 1.6 years; Wisk III intelligence quotient 55.6 ± 11.2) and without ID (n = 13; age = 15.4 ± 1.2 years) performed maximal counter-movement jumps, while knee kinematics, vertical ground reaction forces and electromyographic activity of the vastus lateralis and biceps femoris were captured. Individuals without ID jumped higher than their counterparts with ID and had lower take-off velocity, lower knee joint power and stiffness, lower knee joint extension angle and angular velocity, longer braking and propulsion phase, lower agonist and higher antagonist EMG activity. These results give an insight on possible causes for the performance deficit in CMJ in persons with ID and give the potential for such individuals to improve their ability to jump higher and more efficiently.