Abstract: BACKGROUND: With advancing age older adults often experience a decline in gait termination ability. This may lead to reduced postural and balance control under dual-task conditions, further increasing the risk of falls.
OBJECTIVE: To explore the control strategies during gait termination in older adults under cognitive-motor dural-task conditions.
METHODS: A total of 10 older adults were enrolled in this study, comprising 5 males and 5 females, with a mean age of (60.70±0.64) years. A dual-task paradigm integrating a cognitive task with a gait termination task during walking was adopted. The n-back classic paradigm was used to implement cognitive interventions during gait termination. The lower extremity kinematics and electromyography indicators of 10 subjects were collected using the Vicon infrared motion capture system and Noraxon surface electromyography. Differences in kinematic and electromyography indicators during gait termination (including planned and sudden stopping) under different cognitive loads (0 cognitive load, 1 cognitive load and 2 cognitive load) were compared.
RESULTS AND CONCLUSION: (1) A two-way repeated measures analysis of variance revealed that cognitive load had a significant main effect on ankle angle (P < 0.05), while the two-way interaction was not significant. Stop condition showed a significant main effect on knee angle (P < 0.001), with no significant two-way interaction. For hip angle, both stop condition (P < 0.05) and cognitive load (P < 0.001) exhibited significant main effects, and their two-way interaction was also significant (P < 0.05). During both planned and sudden stops, the ankle plantar flexion angle increased significantly under 2 cognitive load compared with 0 cognitive load (P < 0.05). while, the knee flexion angles showed no significant differences under different cognitive loads (P > 0.05). Compared with 0 cognitive load, the hip flexion angles under 1 and 2 cognitive loads during sudden stop were significantly increased (P < 0.05). (2) A two-way repeated measures analysis of variance revealed that the stopping condition had a significant main effect on the integrated electromyography of  the gastrocnemius, biceps femoris, gluteus maximus, rectus femoris and tibialis anterior (P < 0.05). Cognitive load exhibited a significant main effect on the integrated electromyography of the vastus lateralis and tibialis anterior (P < 0.05). A significant interaction effect was observed between cognitive load and stopping condition for the integrated electromyography of the tibialis anterior (P < 0.001). During sudden stop, the integrated electromyography value of the lateral femoris muscle under 2 cognitive load was significantly increased compared with 0 cognitive load (P < 0.05), and the integrated electromyography value of the anterior tibial muscle was significantly decreased compared with 0 cognitive load (P < 0.05). These results indicate that under dual-task condition, the strategy for gait termination exhibited by older adults in sudden stops is similar to that in planned stops: with cognitive load increasing, gait termination is achieved by greater ankle plantar flexion, knee flexion, and hip flexion angles to absorb impact forces. Moreover, during sudden stop, the angles of ankle plantar flexion, knee flexion, and hip flexion are all larger than those during planned stop.

Key words: older adults, dual tasks, gait termination, biomechanics, cognitive load, electromyography, joint angle, lower limb joint