Denervation and remodeling of motor units (MU) of skeletal muscle is known to occur with ageing and has been demonstrated with EMG measurements of small peripheral muscles in humans (McNeil et al., 2005). However, there is less information about this process in large locomotor muscles that are important for mobility. In the present study, intramuscular EMG (iEMG) was used to examine motor unit potential (MUP) size and duration, in the vastus lateralis muscle. Thirteen active, healthy young men (mean age 26±5y) and 18 active, healthy older men (mean age 73±6y) gave signed, informed consent prior to participation in the study which had been approved by the local ethical committee. Proximal and distal motor points of the vastus lateralis were identified by percutaneous electrical stimulation and iEMG recorded around the motor point with a concentric needle electrode from 3 depths within the muscle and turning the needle through 90° between contractions so that 12 separate recordings were made. Offline analysis was performed on all detected MUPs using Decomposition-Enhanced EMG software (Parsaei et al., 2012). The mean number of MUPs identified and analysed in the young was 32(±9) and in the older subjects 29(±7). The mean area of the MUP was 1165±337 uV.ms for the young and significantly larger at 1690±614 uV.ms for the older subjects (p=0.006). MUP duration was 2.37±0.26 ms for the young and 3.19 ± 0.65 ms for the older subjects, the difference being significant (p=0.002).These results are consistent with substantial motor unit loss (Ireland et al, 2015) and remodeling in the vastus lateralis during healthy ageing as a result of denervation and reinervation and slower propagation of action potentials, possibly associated with an increase in slow units. These changes in motor units may have consequences for motor unit recruitment and control of movements in old age.