Dose-Response and Phase-Specific Effects of Graded Cognitive Load on Functional Mobility in Older Adults: A Kinematic Analysis

Aging is associated with progressive changes in both the central nervous system and the musculoskeletal system, leading to declines in motor performance, balance, and functional mobility. These changes include reduced cortical processing efficiency, slower information processing speed, and alterations in sensorimotor integration, all of which contribute to decreased movement efficiency in older adults. Functional mobility, particularly walking and transitional movements, is no longer considered a purely automatic motor task, but rather a cognitively mediated activity that requires continuous interaction between attentional resources and motor control systems. Clinically, previous studies have demonstrated that dual-task performance is strongly associated with fall risk and mobility impairment in older adults, suggesting 6 its importance in functional assessment and rehabilitation planning.Despite these advances, most of the existing research has primarily focused on binary dual-task paradigms, comparing single-task versus dual-task conditions without considering different levels of cognitive demand. This approach limits the ability to understand whether cognitive-motor interference follows a dose-response relationship, where progressively increasing cognitive load produces graded deterioration in motor performance. Furthermore, while overall gait and mobility outcomes have been widely investigated, there is a lack of detailed evidence regarding how cognitive load influences specific phases of functional mobility tasks, such as sit-to-stand, gait, turning, and stand-to-sit transitions. Previous studies suggest that different movement phases may vary in their sensitivity to cognitive interference due to differences in biomechanical and postural control demands. However, this phasespecific behavior remains underexplored, particularly in the context of graded cognitive loading.

Therefore, there is a clear gap in the literature regarding the combined effect of graded cognitive load and phase-specific motor behavior during functional mobility tasks.

Inclusion criteria

• Age ≥ 60 years
• Ability to ambulate independently without assistive devices
• Ability to follow verbal instructions and perform dual-task activities
• Medically stable and capable of participating in functional mobility assessment Cognitive function within normal range, defined as Mini-Mental State Examination (MMSE) score ≥ 24 out of 30, indicating absence of significant cognitive impairment .
• Functionqal independence in basic activities of daily living, defined as Barthel Index score ≥ 90 out of 100
• Body Mass Index (BMI) between 18.5 and 29.9 kg/m², as values ≥ 30 kg/m² (obesity) may adversely affect gait and balance performance.

Exclusion criteria

• Any neurological disease that affects walking or balance, such as stroke or Parkinson's disease
• Any musculoskeletal condition that limits lower-limb movement or affects normal walking patterns
• Severe cognitive impairment defined as Mini-Mental State Examination (MMSE) score < 24
• Visual, vestibular, or hearing problems that affect safe walking or balance control
• History of lower-limb injury or surgery within the last 6 months
• Serious medical conditions that make participation unsafe, such as unstable cardiac or respiratory disease