Muscle fatigue is characterised by a reduction in force output. Increases in force production are partly mediated by adjustments in motor unit (MU) firing properties however, conflicting research has found MU firing rate to both increase and decrease following fatiguing exercise. This disparity may be influenced by contraction type, as concentric (CON) and eccentric (ECC) contractions are known to require different levels of neural input and result in different responses to fatigue. As a result, other MU properties may also be differentially affected by fatigue depending on contraction type. Acute muscle damage is often more severe following ECC when compared CON contractions, resulting in localised structural, metabolic and functional changes of the muscle. MU firing rate has been demonstrated to increase after damage resulting from ECC exercise, yet the effects of ECC exercise on peripheral MU properties as a result of damage remains unknown. A better understanding of the contraction specific MU responses is important when considering training protocols and injury risk, particularly in populations with musculoskeletal impairments. This talk will address the effects of CON and ECC muscle fatigue and acute muscle damage on MU function using a combination of intramuscular and high-density surface electromyography methods.