Abstract
Normal aging results in alterations in the visual, vestibular and somtaosensory systems, which in turn modify the control of balance. Muscle fatigue may exacerbate these age-related changes in sensory and motor functions, and also increase the attentional demands associated with dynamic postural control. The purpose of this study was to investigate the effect of aging on dynamic postural control and posture-related attentional demands before and after a plantar flexor fatigue protocol. Participants (young adults: n = 15; healthy seniors: n = 13) performed a dynamic postural task along the antero-posterior (AP) and the medio-lateral (ML) axes, with and without the addition of a simple reaction time (RT) task. The dynamic postural task consisted in following a moving circle on a computer screen with the representation of the center of pressure (COP). This protocol was repeated before and after a fatigue task where ankle plantar flexor muscles were targeted. The mean COP-target distance and the mean COP velocity were calculated for each trial. Cross-correlation analyses between the COP and target displacements were also performed. RTs were recorded during dual-task trials. Results showed that while young adults adopted an anticipatory control mode to move their COP as close as possible to the target center, seniors adopted a reactive control mode, lagging behind the target center. This resulted in longer COP-target distance and higher COP velocity in the latter group. Concurrently, RT increased more in seniors when switching from static stance to dynamic postural conditions, suggesting potential alterations in the central nervous system (CNS) functions. Finally, plantar flexor muscle fatigue and dual-tasking had only minor effects on dynamic postural control of both young adults and seniors. Future studies should investigate why the fatigue-induced changes in quiet standing postural control do not seem to transfer to dynamic balance tasks.
Highlights
The accomplishment of daily living activities, such as leaning over to grab an object, requires adequate postural control to maintain the center of gravity within the base of support (BOS)
We aimed to compare the effects of a plantar flexor fatigue protocol on dynamic postural control and posturerelated attentional demands between young adults and seniors
In half of the trials, a secondary auditory-verbal reaction time (RT) task was added to probe the attentional demands associated with dynamic postural control
Summary
The accomplishment of daily living activities, such as leaning over to grab an object, requires adequate postural control to maintain the center of gravity within the base of support (BOS). For this purpose, the central nervous system (CNS) must continuously integrate different sources of sensory information (mainly from the visual, vestibular and somatosensory systems), while generating appropriate motor commands to perform balance corrections (Diener and Dichgans, 1988). Postural balance is threatened by internal and/or external perturbations. In parallel, aging is accompanied by multiple changes in neuromuscular structures and function, a loss of spinal motoneurons and a reduction in muscle fiber number and size, which impair motor performance (Aagaard et al, 2010) and decrease the ability of seniors to adapt to postural perturbations and recover from a loss of balance (Bugnariu and Sveistrup, 2006)
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