Age-related decline of gait control under a dual-task condition.

Abstract

To the Editor: Age-related changes in spatial and temporal gait parameters have been associated with an adaptation to a safer gait and an increased risk of falling.1 In particular, high stride-to-stride variability was found to be a dependable and potent predictor of falls in community-dwelling older adults. In fact, a small increase in stride-to-stride deviation for stride length of 0.017 m doubled the likelihood of future falling.2 Inability to walk and talk at the same time (“stops walking while talking”) is also associated with an increased risk of falling.3 Little information is available about the effect of an attention-splitting task on the gait variability of older adults.4 The aim of this study was to compare stride-to-stride variation in stride length and velocity of community-dwelling older and young adults who were asked to walk while counting backward. Twelve older adults (11 women and 1 man, mean age ± standard deviation (SD) = 83.4 ± 7.7) and 12 young control subjects (11 women and 1 man, mean age ± SD = 22.5 ± 2.4) volunteered to participate. All older adults met the following inclusion criteria: aged 70 and older, no fall history, Mini-Mental State Examination (MMSE) score of 20 or greater, able to walk without a walking aid, and no major neurological or orthopedic problems. The participants were asked to perform two different tasks: walking as a single task and walking while counting backward out loud from 50. Subjects completed one trial for each of the walking conditions on a 15-meter walkway in a well-lit environment, at their own speed, and wearing their own footwear. The human investigation committee approved the project, and written informed consent was obtained before testing. Stride length (m) and stride velocity (m/s) were determined during steady-state walking using an ambulatory device (Physilog, BioAGM, Lausanne, Switzerland) and sensors attached on both lower extremities.5 Stride-to-stride variability was determined by calculating the coefficient of variation (CV = (SD/mean) × 100) for stride length and stride velocity. The Wilcoxon rank-sum test was used to compare coefficients of variation between the two walking conditions. P-values less than .05 were considered statistically significant. Stride-to-stride variability of stride length and stride velocity increased significantly in older subjects with the interfering task of counting. No significant change in gait variability was found in young subjects (Table 1). These results represent, to the best of our knowledge, the first report demonstrating that a dual task increases stride-to-stride variability in older subjects. Walking is a highly automated, rhythmic motor behavior that is mostly controlled by subcortical locomotor brain regions.6 The added task of counting backward interfered with gait regularity in older adults only. This strongly suggests the involvement of higher cortical regions for the motor control of gait in this population. This is consistent with other evidence that walking requires a higher level of attention and thus more cortical involvement with increasing age.7 The inability to allocate attention properly between walking and counting backward could explain the high stride-to-stride variability in these older sample. A dual-task-dependent increase in stride-to-stride variability appears to be a marker for age-related decline in gait control in older adults and might prove to be a particularly sensitive method for the identification of older subjects prone to falling. Further research is needed to define the potential association between falls and increased gait variability under dual-task conditions and to explore interventions that could favorably affect stride-to-stride variability of older adults.