The Multiple Tasks Test: development and normal strategies.
Simultaneous challenge of posture and cognition ("dual tasks") may predict falls better than tests of isolated components of postural control. We describe a new balance test (the Multiple Tasks Test, MTT) which (1) is based upon simultaneous assessment of multiple (>2) postural components; (2) represents everyday situations; and (3) can be applied by clinicians. Relevant risk factors for falls and actual fall circumstances (identified from a prospective survey in Parkinson's disease) were used to design functional tests (or postural "components") that resembled everyday situations. We distinguished a "cognitive" component (answering serial questions) from largely "motor" components (standing up, sitting down, turning around, walking, avoiding obstacles, and touching the floor). Four additional components included carrying an empty or loaded tray, wearing shoes with slippery soles and reduced illumination. These components were combined to yield eight separate tasks of increasing complexity that were executed sequentially. The first and simplest task consisted of standing up, undisturbed walking, turning around and sitting down. For each of the next tasks, a new component was added to the earlier and otherwise identical task. All components within each task had to be performed simultaneously. Errors were defined as Hesitations (slowed performance) or Blocks (complete cessation), which were scored separately for execution of motor and cognitive components. Speed of performance was not stressed, but was measured for all tasks. The MTT was administered to 50 young healthy subjects (mean age 27.6 years) and 13 elderly subjects (mean age 62.0 years). To study learning effects, 20 different young subjects (mean age 21.0 years) received the MTT in order of gradually decreasing complexity. For subjects who received the MTT in order of increasing difficulty, 62% in both age groups performed all eight tasks without any Errors in the motor components. Among those making Errors, the proportion of subjects that made motor Errors increased significantly as the tasks became more complex (F(1,7)=2.66, P<0.05). This increase differed across the two groups (significant interaction of Group by Task; F(1,7)=3.07, P=0.01) because more elderly subjects produced motor Errors during the most complex tasks. Cognitive Errors increased even more than motor Errors with task complexity, and this increase was most pronounced in young subjects (significant interaction of Group by Error Type by Task; F(1,1,7)=3.85, P=0.001). Only eight young (16%) and four elderly subjects (30.8%) performed the MTT without any motor or cognitive Errors, again suggesting that more young subjects made cognitive Errors. Among subjects who received the MTT in reverse order, motor errors were more common than among subjects who received the MTT in order of increasing complexity (F(1,7)=5.90, P<0.05), particularly during the two most difficult tasks. The elderly performed all tasks slower than the young subjects. We conclude that the MTT is a new balance test based upon a multiple task design that resembles everyday situations. Performance by healthy subjects revealed interesting insights into normal postural strategies. For complex postural tasks, healthy subjects favour execution of motor components over execution of a cognitive component ("posture first" strategy). Young subjects were more inclined than elderly subjects to use this strategy. Motor learning influenced performance among subjects who received the MTT in order of increasing difficulty. Further studies must determine whether the MTT can be used to evaluate balance disorders.