Objective To investigate the association of asymmetry in leg extension power (LEP) with walking and standing balance.

Design Cross-sectional analysis.

Setting Research laboratory.

Participants Healthy female twins (N=419), ages 63 to 75 years.

Interventions Not applicable.

Main Outcome Measures The LEP difference between the stronger and the weaker leg, measured with the Nottingham power rig, was calculated. Ten-meter maximal walking velocity was assessed in a laboratory corridor on a wide (170cm) and narrow (35cm) track, and the ability to maintain tandem stance for 20 seconds was recorded.

Results The mean LEP difference ± standard deviation between the legs was 15%±9% (P<.001). Those with large LEP difference had lower walking velocity and poorer standing balance than those with small LEP difference, in particular when the LEP of the stronger leg was below the median.

Conclusions Even in healthy older women, substantial LEP asymmetry between the lower limbs was present, encumbering walking and standing balance. Lower-limb muscle power asymmetry warrants further study in order to develop well-targeted strategies for preventing mobility limitation in older people.