The purpose of this study was to quantify the association between low-frequency fatigue (LFF) and the increase in EMG and force fluctuations after eccentric exercise of elbow flexor muscles. Ten subjects performed two tasks involving voluntary isometric contractions of elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at 5 submaximal target forces (5, 10, 20, 40, 60% MVC) while electromyography (EMG) was recorded from biceps and triceps brachii. A third task involved electrical stimulation of biceps brachii at twelve frequencies (1-100 Hz). These tasks were performed before, after, 2-hrs and 24-hrs after concentric or eccentric exercise. MVC force declined after eccentric exercise (34% decline) and remained depressed 24-hrs later (22% decline), whereas the reduced force following concentric exercise (32%) was recovered 2-hrs later. Biceps brachii EMG and force fluctuations during the submaximal voluntary contractions increased after eccentric exercise (both ~2x greater) with the greatest effect at low forces. LFF was equivalent immediately after both types of exercise (50-60% reduction in 20:100 Hz force) with a slower recovery following eccentric exercise. A significant association was found between the change in LFF and EMG (r² values up to 0.52), with the strongest correlations observed at low forces (20% MVC) and at 2-hours after exercise. In contrast, there were no significant associations between LFF and force fluctuations during voluntary or electrically-evoked contractions, suggesting that other physiological factors located within the muscle are likely to be playing a major role in the impaired motor performance after eccentric exercise.