We investigated the relationship between macro-EMG and muscle Uber conduction velocity in the right biceps brachii in 5 normal subjects using a single-Uber macroelectrode and surface array electrodes. The macro-EMG signal and the surface electrode signals were triggered and averaged by the single-Uber action potential. The amplitude and area of the macro-EMG was correlated with the muscle Uber conduction velocity, suggesting that the macro-EMG can serve as a parameter of the size principle in both the clinical and research settings.