In vastus lateralis (VL), around ~40% of motor units (MUs) are lost by age 70 even in active older men, whilst remaining MUs are around 25% larger due to collateral reinnervation of orphaned fibres (Piasecki et al. 2015). This remodelling is accompanied by reduced stability (indicated by increased MU potential (MUP) variability, or ‘jiggle’) and firing rate in remaining units. There is some evidence that exercise is effective in attenuating MU loss (Power et al., 2010), although it is unknown whether remodelling is affected. Therefore, intramuscular electromyographic signals were recorded at proximal and distal motor points of (VL) in 26 young males (age 25±5y), 22 old males (71±5y) and 15 Master athletes (MA, 70±6 yrs) during contractions at 25% of knee extension maximum voluntary contraction (MVC). Data were analysed using decomposition-based quantitative electromyography (DQEMG) to identify characteristics of individual MUPs, resulting in 698, 627 and 414 detected MUPs in young, old and MA respectively. Jiggle was assessed following application of a ‘near fibre’ method to examine only contributions from fibres located very close to the electrode, thereby reducing artefact or attenuation. Group effects were assessed using one-way ANOVA, with Bonferroni-corrected posthoc tests used to locate group differences. Firing rates were normally distributed and are reported as mean(SD). MUP size and jiggle were not normally distributed; they were log transformed prior to analysis and are presented as median(IQR). Median MUP size was 62% and 18% larger in MA than young and old respectively, whilst old median MUP size was 37% larger than young (Table 1, all P<0.001). Jiggle and firing rate did not differ between old and MA (both P>0.5), but values in both groups were higher and lower respectively than in young (all P<0.05). Regular exercise does not prevent age-associated MU remodelling. Conversely, remodelling is more pronounced in highly active older males but this is not accompanied by greater slowing of MUs or MU instability above that observed in healthy ageing. Exercise participation may improve effectiveness of reinnervation following MU loss, contributing to preservation of muscle size and strength in older age.