Lift speed moderates the effects of muscle activity on perceived heaviness

Research has shown that perceived heaviness is a function of the ratio of muscle activity (measured by electromyogram [EMG]) to the resulting acceleration of the object. However, objects will commonly be lifted at different speeds, implying variation in both EMG and acceleration. This study examined the effects of lifting speed by having participants report perceived heaviness for objects lifted by elbow flexion at three different speeds: slow, preferred, and fast. EMG and angular acceleration were recorded during these lifts. Both EMG and angular acceleration changed across lift speed. Nevertheless, despite these variations, perceived heaviness consistently scaled to the ratio of EMG to angular acceleration. The exponents on these parameters suggested that the saliency of muscle activity and movement changed across the three lift speeds.