Abstract
Motor abundance allows individuals to perform any task reliably while being variable in movement's particulars. The study investigated age-related differences in this feature when young adults (YA) and older adults (OA) performed challenging tasks, namely treadmill walking alone and while performing a cognitive task. A goal function for treadmill walking was first defined, i.e., maintain constant speed at each step, which led to a goal equivalent manifold (GEM) containing all combinations of step time and step length that equally satisfied the function. Given the GEM, amounts of goal-equivalent and non-goal-equivalent variability were afterwards determined and used to define an index providing information about the set of effective motor solutions relative to the GEM. The set was limited in OA compared to YA in treadmill walking alone, indicating that OA made less flexible use of motor abundance than YA. However, this differentiation between YA and OA disappeared when concurrently performing the cognitive task. It is proposed that OA might have benefited from cognitive compensation.
Highlights
Walking is a complex task whose performance relies on the sensorimotor system and critically depends on cognitive resources, executive function that orchestrates goaldirected activities [1,2]
Age-related differences in single-task treadmill walking During single-task treadmill walking, older adults (OA) exhibited a lower relative proportion of variability along the goal equivalent manifold (GEM) than young adults (YA), due to lower sðdT Þ and larger sðdPÞ
This result confirmed our hypothesis: the body-level degrees of freedom were more constrained in OA than in YA, giving rise to a more limited set of effective motor solutions relative to the GEM for successful treadmill walking
Summary
Walking is a complex task whose performance relies on the sensorimotor system and critically depends on cognitive resources, executive function that orchestrates goaldirected activities [1,2]. Studies reported an agerelated dual-task deficit while walking overground, which includes larger decreased speed and increased stride-to-stride variability in older adults (OA) than in young adults (YA) [5,6,7,8]. This deterioration of the dual-task ability with normal aging was observed in treadmill walking, with larger changes in the variability of the gait patterns when increasing cognitive task difficulty in OA as compared to YA [9,10]. A likely explanation for these results is that gait control increasingly relies on cognitive processes with aging and agerelated neurodegenerative diseases while at the same time attentional capacity and other relevant cognitive resources (‘‘cognitive supply’’) are reduced [14]
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