Short term overload of the eccentric phase of a contraction leads to superior strength gains than conventional contractions despite a matched workload (3). Adaptations from these interventions have been shown to come from increases in IIX fibre cross sectional area (2). Initially, however it is likely that these strength adaptations will occur from increases in neural drive (4). Therefore, it is possible that there is an acute neural response from the larger motor units to eccentric overload that contributes to this stimulus. Accordingly, it was the purpose of this study to investigate motor unit firing rates following an acute accentuated eccentric load (AEL) protocol in comparison to constant load (CL) protocols. Additionally, these interventions were performed at 2 different eccentric velocities (full knee extension to flexion: 4 or 2 seconds). Healthy, resistance trained males (n=10) attended the laboratory on 4 separate occasions: they completed 3 concentric repetition maximum contractions (3RM) following a warm up. They then performed a maximal isometric voluntary contraction (MVC) followed by a submaximal 10 second contraction (70% of MVC) during which high density surface electromyography (1) recorded firing rate of all motor units from the vastus lateralis. Then, they either did CL (2s), AEL (2s), CL (4s) or AEL (4s) in random order. AEL and CL consisted of eccentric load at 120% and 85% of 3RM respectively and both with a concentric load of 85% of 3RM where they were encouraged to contract maximally. The contractions consisted of 3 sets (3 minute recovery) of 3 repetitions. Then the participants repeated the MVC and submaximal 10 second contraction. Values are mean + SD and compared by ANOVA. For all 4 interventions no alterations where shown in MVC following the exercise, neither was there any differences in concentric velocity during the contractions. The only changes observed were following the fast (2s) interventions during the submaximal isometric contractions where the larger motor units recruited (represented by the final third in order of recruitment), significantly (p<0.05) declined following AEL (2s) in comparison to CL (2s) (AEL: pre:10.8 + 2.9 post 8.8 + 1.7 pps vs CL: pre 10.3 + 2.9 post 11.2 + 2.2 pps), whereas no changes were observed in the smaller motor units. In addition, no alterations were shown for the number of motor units recruited for any of the interventions. In conclusion, it is likely that the larger motor units fatigued following the faster acute eccentric overload intervention without any maximal force capacity decrements. It may be this initial stimulus that contributes to the superior adaptation of eccentric overload previously reported.