Dell'Oro, Lisa Ann (2008) The contribution of divided attention to tripping while walking. PhD thesis, Victoria University.

Abstract

Falls in older adults has long been recognised as a significant public health problem requiring urgent intervention. Tripping while walking is one of the most commonly cited reasons for falls, however, little research has focused so far on foot motion characteristics and their contribution to the likelihood of tripping while walking. Even fewer studies have examined tripping on unseen obstacles while obstacle negotiation (i.e. tripping on seen obstacles) has received more attention. The primary aim of this research was to examine foot motion during long-term (e.g., 30 minutes) continuous treadmill walking by measuring minimum toe clearance (MTC), the very small distance the foot clears the ground during swing phase of gait. Examining MTC of each stride allowed an estimation of the likelihood of an individual tripping on unseen obstacles while walking. Since cognitive decline and reduced ability to multitask (reduced divided attention capacity) has been observed in older adults and has been linked to falls risk, this research also examines foot kinematics during distracted walking conditions. Foot motion was analysed during undistracted and distracted walking using various short (turning the head to identify objects to the left and then the right; reacting to a visual stimulus by pressing a hand-held button; reaching into a waist pouch to retrieve a handkerchief; and a cough) and prolonged distractions (counting backwards by threes; and watching a video) that could be encountered in normal everyday life. This enabled an evaluation of the types of distractions and situations that might increase the risk of tripping in healthy elderly females. This research, therefore: (1) focused on healthy elderly females (n = 18, mean age 71.3 years, SD = 3.6 years) and healthy young females (n = 18, mean age 21.8 years, SD = 3.6 years); (2) utilised a 2D model of the foot to using shoe dimension to calculate MTC at midswing; (3) calculated probability of tripping for each subject based on individual MTC distributions; and (4) examined MTC descriptive statistics during undistracted walking at a self-selected comfortable walking speed on the treadmill for ~20 minutes and during various everyday distractions (short and prolonged) for 10 minutes. Descriptive statistics of individual MTC distributions, which included between 906 to 1253 strides per subject, were examined. For undistracted walking, the elderly adults had lower measures of all variables in the lower end of the MTC distribution, namely minimum (minMTC) (1.08cm vs. 1.42cm, p<.05), first percentile (PC1MTC) (1.35cm vs. 1.68cm, p<.05), fifth percentile (PC5MTC) (1.50cm vs. 1.81cm, p<.05), and first quartile (Q1MTC) (1.80cm vs. 2.00cm, p<.05). The higher skewness of MTC distributions (0.60 vs. 0.33, p<.05) in the elderly, however, suggests some attempt was made to reduce the frequency of MTC in the lower portion of the distribution. It was discovered that an individual’s calculated frequency of tripping was approximately once every second stride when MTC was approximately equal to the individual’s MTC distribution central tendency (median). Elderly subjects had greater calculated probability of tripping (PT) between MTC(y) = 0.9cm – 2.0cm (p<.05). The elderly also had higher intra-individual variability in MTC as measured by interquartile range (IQRMTC) (0.44cm vs. 0.28cm, p<.01). For normal undistracted walking, the elderly are at an increased risk of tripping on unseen obstacles given the smaller MTC and greater variability in MTC. For the distracted walking conditions, the elderly had significantly lower medianMTC compared with the young for most distraction tasks (p<.05). The elderly also typically had lower minMTC and higher IQRMTC compared with the young. The lower MTC and higher intra-individual variability due to distractions places the elderly at an increased risk of tripping on small unseen obstacles compared with the young. The distraction eliciting the smallest MTC was a prolonged task (60 seconds) and involved structural interference where vision was focused on the task as well as maintaining posture and balance (video task). Distractions such as observing the scenery while walking therefore could increase the likelihood of tripping. The largest MTC was during the head turn task, where subjects turned the head to identify objects to the left and right. This large MTC could have been an attempt to reduce the likelihood of tripping.

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