• Primary outcomes

Gait speed was recommended by the US FDA as one of the two functional tests to be used as outcomes in pharmacological trials because of its good validity, reliability, sensitivity to change and predictive validity for multiple adverse outcomes [33]. Research assistants conduct gait evaluations using a computerized mat (180 × 35.5 × 0.25 inches) with embedded pressure sensors (GAITRite; CIR Systems, PA, USA). Participants are asked to walk on the mat at their ‘normal walking speed’ in a quiet and well-lit room. Our primary outcome is gait speed (cm/s). However, multiple gait parameters are obtained and available for analyses [34]. We have reported excellent test–retest reliability of gait speed on GAITRite (κ >0.9) [35].

The WWT paradigm has been widely studied as a real world test of divided attention to examine cognitive-motor interactions. The WWT test is a novel, reliable and ecologically valid mobility measure developed by our group [36–38]. Our studies have established the incremental validity of WWT over NPW speed for predicting adverse outcomes such as falls, frailty and disability [36,37]. Participants are instructed to walk on the mat, as described above, while performing a cognitive interference task, which is reciting alternate letters of the alphabet starting with the letter ‘A’. They are instructed to pay equal attention to walking and talking to minimize task prioritization effects [36,38]. The number of errors and correctly recited alternate letters are recorded. There was good inter-rater reliability in our previous studies (r = 0.602) [36].