Age-associated decline in muscle mass and strength impairs functional mobility in older adults. We examined the effects of an eccentric endurance exercise programme (downhill treadmill walking, DTW) at a self-selected walking speed (SSWS) on functional mobility and eccentric and concentric strength of m. quadriceps femoris of older adults. Twenty-four older adults (67 ± 4 years) were randomly assigned to complete 3 × 30 min treadmill walks per week for 12 weeks on a level (n = 11, LTW 0%) or downhill (n = 13, DTW -10%) treadmill gradient at SSWS. SSWS was re-adjusted every 4 weeks. Participants were assessed for five repetition sit-to-stand (5-RSTS), maximal walking speed (MWS), timed up-and-go (TUG) and dynamic strength. SSWS was similar for both groups with increases from 1.18 ± 0.11 to 1.53 ± 0.09 m s(-1) (LTW) and 1.26 ± 0.16 to 1.61 ± 0.12 m s(-1) (DTW) (time, P < 0.01). Improvements in 5-RSTS, MWS and TUG were substantial and similar for both groups (time, P < 0.01). 5-RSTS (baseline LTW: 8.50 ± 1.19 s, DTW: 8.54 ± 1.52 s) improved by 32 and 34%. MWS (baseline LTW: 2.39 ± 0.38 m s(-1), DTW: 2.40 ± 0.33 m s(-1)) improved by 22 and 23%. TUG (baseline LTW: 5.58 ± 0.51 s, DTW: 5.46 ± 0.89 s) improved by 22% for both groups. Peak eccentric and concentric torque did not change. Knee angle of concentric peak torque (180° s(-1)) was decreased after 12 weeks in both groups (LTW: 37° ± 16° to 26° ± 14°, DTW: 42° ± 18° to 37° ± 16°, P < 0.05). Regular level and downhill treadmill walking by older adults, at a SSWS, results in substantial improvements in functional mobility. Changes in functional mobility were not explained by changes in dynamic strength of the m. quadriceps femoris.