Table 1.

Secondary tasks prescribed during perturbation-based training

Type of ongoing task†	Description
Repetitive movement of upper body	Reaching out in front (alternating hands) Reaching up (alternating hands) Reaching down (alternating hands) Alternately reaching up, out and down Reaching out to the side Trunk twists (side to side, keep head looking forward) Swinging arms (alternating), as if 'brisk walking'
Repetitive movement of lower body	Walking in place Shallow knee bends
Cognitive tasks	Words beginning with a letter (e.g. 'A': "apple, arrive") Words belonging to a category (e.g. 'girls names': "Mary, Anne") Counting backwards by 3's Backwards alphabet ("z y x w v u t......") Words that rhyme with a specified word (e.g. 'chair': "air, hair, fair") Multi-syllable word spelling (e.g. 'Mississauga') Subtracting 13, 17 or 19 from a number Talk about a topic (e.g. "tell me about the last book you read")
Held object‡	Plastic shopping bag Umbrella Book Handbag (women only)

^†Type of task varies every eight perturbation trials.

^‡For grasping training, subjects are asked to hold one of these items in their right hand and drop it in order to effectively grab the rail following the perturbation. These objects are also held for some sets during stepping training, but subjects are instructed to continue holding the object as there is no handrail nearby for them to grasp.