Abstract In order to understand how the central nervous system controls the kinematics of rapid finger and hand movements, we studied the motions of subjects turning a knob to light-emitting diode targets, similar to tuning a radio dial. On many trials, subjects turned the knob with a single, smooth, and regular motion as revealed by the angular position and velocity trajectories, but on others, subjects produced irregularities in the kinematics. Like many past studies, we interpreted these irregularities as discrete corrective submovements. Unlike other studies, we used a direct, objective algorithm to identify overlap- ping submovements, detecting appreciable inflections in the acceleration traces by examining zero crossings in their derivatives, jerk and snap. The movements without overlapping submovements on average had a near sym- metric, bell-shaped velocity profile that was independent of speed, and which matched the theoretical minimum jerk velocity very closely. We proposed three plausible mechanisms for altering the shape of movement kine- matics, and implemented a mass-spring model with non- linear damping to explore the possibilities. Although there was relatively little variability in the shape and symmetry of movements across trials, there was a fair amount of variability in their amplitude. We show that subjects attempted to eliminate the need for corrective submovements by making more accurate primary move- ments with practice, but that the variability inherent in rapid movements dictated the need for corrective sub- movements. Subjects used corrective submovements to improve final endpoint accuracy while reducing endpoint variability, resulting in higher task success rates. Key words Hand movements · Kinematics · Symmetry · Submovements · Model Introduction Every day we use our hands and fingers to grasp and ma- nipulate objects in our environment with incredible coor- dination and skill. A disproportionate amount of the brain’s motor cortex is devoted to these complicated hand skills necessary for interacting with the world around us. To gain insight into how we use our hands to manipulate objects and how we achieve accuracy in rap- id hand movements, this study investigates the kinemat- ics of a coordinated multijoint hand manipulation task. Subjects were required to turn a knob rapidly to align a pointer with a target. The movement was complicated, with the possibility of eighteen degrees of freedom with all the finger joints. In studying the kinematic features of simpler move- ments, some investigators (Abend et al. 1982; Atkeson and Hollerbach 1985; Flash and Hogan 1985; Gordon et al. 1994; Morasso 1981; Uno et al. 1989) have ob- served smooth, nearly symmetric movement trajectories. Others (Berthier 1996; Crossman and Goodeve 1983; Flash and Henis 1990; Keele 1968; Krebs et al. 1998; Lee et al. 1997; Meyer et al. 1988; Milner 1992; Morasso and Mussa Ivaldi 1982; Pratt et al. 1994; Woodworth 1899) have described irregularities in move- ments produced as a series of discrete submovements, or substantial asymmetries in the trajectories (Moore and Marteniuk 1986; Nagasaki 1989; Wiegner and Wierzbicka 1992). Many movements contain irregulari- ties and multiple velocity peaks near the end of a move- ment when high spatial precision is required (Crossman and Goodeve 1983). The iterative-corrections model of Keele (1968) and Crossman and Goodeve (1983) proposed that a series of submovements of a constant movement time and succes- sively smaller amplitudes were generated one after the other until the target was reached. Meyer et al. (1988) recognized a shortcoming of this model in its inability to deal with movement variability, and proposed a “sto- chastic optimized-submovement model.” In this model one or more submovements may be made after the pri- K.E. Novak ( ✉ ) · L.E. Miller · J.C. Houk Department of Physiology, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3107, USA e-mail: k-novak@nwu.edu K.E. Novak · J.C. Houk Department of Biomedical Engineering, Northwestern University, 303 E. Chicago Avenue, Ward 5–150, Chicago, IL 60611, USA Exp Brain Res (2000) 132:419–433 Digital Object Identifier (DOI) 10.1007/s002210000366 RESEARCH ARTICLE K.E. Novak · L.E. Miller · J.C. Houk Kinematic properties of rapid hand movements in a knob turning task Received: 26 October 1999 / Accepted: 28 January 2000 / Published online: 25 March 2000 © Springer-Verlag 2000