Compared to high-dose epidurals where mobility is impossible, mobile epidurals have been shown to reduce instrumental vaginal delivery rates. The mechanism for this benefit may depend on women walking or adopting upright postures during labour. We investigated maternal motor power and ambulation of 1052 primparous women randomised to high-dose epidural (Control), Combined Spinal Epidural (CSE) or Low-Dose Infusion (LDI) as a pre-specified, secondary outcome of the Comparative Obstetric Mobile Epidural Trial. Modified Bromage power scores and the level of mobility a woman actually achieved were recorded each hour after epidural placement during first and second stage, until delivery. Relative to control, significantly more women maintained normal leg power throughout labour in both mobile groups and significantly more women with CSE maintained superior leg power for longer than with LDI. Observational analysis did not demonstrate an association between the level of ambulation a woman actually achieved after epidural placement and delivery mode.