Strength, power, and coactivation in children with developmental coordination disorder

Strength, power, and coactivation levels were measured during knee extension and flexion tasks in 20 children (13 males, 7 females) with developmental coordination disorder (DCD) and 20 age-matched control children (12 males, 8 females). Participants were classified according to results obtained on the McCarron Assessment of Neuromuscular Development, with each group including two age levels: 6 to 7 and 9 to 10 years. Tasks were performed on a Biodex dynamometer under isometric and isokinetic conditions with surface EMG recorded from the vastus lateralis and biceps femoris muscles. Significant effects of group and age were observed for the measures of peak torque (isometric and isokinetic) and power, with the decreased power in the group with DCD being more apparent at higher velocities. A lower flexor-extensor percentage was recorded for the group with DCD but only under isokinetic conditions. From a neuromuscular perspective, the group with DCD had increased levels of coactivation (RMS agonist:RMS antagonist) during the isometric flexion and isokinetic extension actions. Possible causes of the strength and power deficits observed in children with DCD are discussed.