Determination of the optimal braking force (Fopt in the Wingate Anaerobic Test (WAnT) among healthy people has been determined based on total body mass. The abnormal muscle mass to total body mass ratio in individuals with neuromuscular disabilities invalidates this approach. This study was intended to validate the optimal force obtained from the Force Velocity Test(FVT) and from an estimate of lean arm volume as two alternative predictors for the Fopt. Twenty-eight 6- to 16-yr-old girls and boys with neuromuscular diseases performed the arm WAnT six times (three trials in each of two visits) against various braking forces to directly determine Fopt. They also performed the arm Force Velocity Test to assess optimal force (FoptFVT). Lean arm volume was determined by anthropometry (ALV) and water displacement (WLV). Correlations between Fopt on the one hand, and FoptFVT, WLV, and ALV on the other, were: R2 = 0.91, 0.81, and 0.82, respectively. Total body mass was the worst predictor (R2 = 0.65). Thus, Fopt obtained from either FVT or lean arm volume estimate is a useful predictor of the Fopt for mean power of the WAnT in children and adolescents with a neuromuscular disability.