The purpose of this study was to determine the effect of eccentric exercise on correlated motor unit discharge (motor unit synchronization and coherence) during low-force contractions of the human biceps brachii muscle. Eight subjects (age 25 ± 7 years) performed three tasks involving isometric contraction of elbow flexors while electromyographic (EMG, surface and intramuscular) records were obtained from biceps brachii. Tasks were: 1) maximum voluntary contraction (MVC); 2) constant-force contraction at various sub-maximal targets; and 3) sustained discharge of pairs of concurrently active motor units for 2-5 minutes. These tasks were performed before, immediately after, and 24-hrs after fatiguing eccentric exercise. MVC force declined 46% immediately after eccentric exercise and remained depressed (31%) 24-hrs later, which is indicative of muscle damage. For the constant-force task, biceps brachii EMG (~100% greater) and force fluctuations (~75% greater) increased immediately after exercise, and both recovered by ~50% 24-hrs later. Motor unit synchronization, quantified by cross-correlation of motor unit pairs during low-force (1-26% MVC) contractions, was 30% greater immediately after (n=105 pairs) and 24-hrs after exercise (n=92 pairs) compared with before exercise (n=99 pairs). Similarly, motor unit coherence at low (0-10 Hz) frequencies was 20% greater immediately after exercise and 34% greater 24-hrs later. These results indicate that the series of events leading to muscle damage from eccentric exercise alters the correlated behavior of human motor units in biceps brachii muscle for at least 24 hours after the exercise.