Ballistic movement can be defined as muscle contractions that exhibit maximum velocities and accelerations over a very short period of time. They exhibit high firing rates, high force production, and very brief contraction times. Physiology Muscle contraction The muscle contraction of a ballistic muscle movement can exhibit a muscle coactivation of concurrent agonist and antagonist muscles or the characteristic triphasic agonist/antagonist/agonist muscle activation. Electromyography (EMG) recordings of demonstrate the triphasic muscle activation begins with a brief agonist motor unit activation signal with firing rates of 60 to 120 Hz that may last for 100ms and occurs 50 to 100ms before movement begins. The firing rates of ballistic movements are much higher than that of slow ramp movements (5–15 Hz). The brief agonist muscle contraction is thus followed by antagonist muscle unit activation. The degree of antagonist muscle unit activation is dependent on the task at hand unlike the first agonist muscle activation which is independent to environmental stimuli. The function of the antagonist muscle contraction is believed to control the amplitude and timing of ballistic movements. Antagonist muscle contraction may serve to prevent injury to joints by preventing the limb from overextending itself and also function to control the distance and time the limb is being moved. Experiments involving ballistic movement of small amplitudes show a marked increase in antagonist muscle activation and experiments where distance moved is not controlled antagonist muscle activation was decreased or absent. The second agonist muscle activation is suggested to terminate the negative acceleration of the antagonist muscle contraction and thus the ballistic movement. Power and energetics Elastic storage of energy Ballistic movements are often powered through elastic energy storage and subsequent recovery mechanisms. The power required to produce the extremely rapid velocities of ballistic movements is made possible through muscle work being stored in elastic elements (such as tendons, aponeuroses, or even muscle). Muscle work is applied to these elastic elements over a relatively slow period of time, and is released very rapidly. Higher power output is produced because the energy is released in a much shorter amount of time than it is stored. In this sense the power of the muscles is actually amplified. When energy is produced by muscle contraction, stored in a tendon, then released to increase mechanical energy of the body (or body segment), muscle power is amplified. It is important to note, however, that the term power ‘amplification’ may