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Salman Nazary-Moghadam, Mahyar Salavati, Ali Esteki, Behnam Akhbari, Sohrab Keyhani and Afsaneh Zeinalzadeh

Objectives: The current study assessed the intrasession and intersession reliability of the knee flexion–extension Lyapunov exponent in patients with anterior cruciate ligament deficiency and healthy individuals. Study Design: University research laboratory. Methods: Kinematic data were collected in 14 patients with anterior cruciate ligament deficiency and 14 healthy individuals walked on a treadmill at a self-selected, low, and high speed, with and without cognitive load. The intraclass correlation coefficient, standard error of measurement, minimal metrically detectable change, and percentage of coefficient of variation were calculated to assess the reliability. Results: The knee flexion–extension Lyapunov exponent had high intrasession reliability, with intraclass correlation coefficients ranging from .83 to .98. In addition, the intersession intraclass correlation coefficient values of these measurements ranged from .35 to .85 regardless of group, gait speed, and dual tasking. In general, relative and absolute reliability were higher in the patients with anterior cruciate ligament deficiency than in the healthy individuals. Conclusions: Although knee flexion–extension Lyapunov exponent demonstrates good intrasession reliability, its low intersession reliability indicates that changes of these measurements between different days should be interpreted with caution.

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Shahrzad Mohammadi-Rad, Mahyar Salavati, Ismail Ebrahimi-Takamjani, Behnam Akhbari, Shiva Sherafat, Hossein Negahban, Pezhman Lali and Masood Mazaheri

Purpose:

To compare the effect of dual tasking on postural stability between patients with anterior cruciate ligament reconstruction (ACL-R) and healthy controls.

Methods:

Single-limb postural stability was assessed in 17 athletes with ACL-R and 17 healthy matched athletes while standing on a Biodex Balance System platform in 4 conditions: stability level of 8 (ie, more-stable support surface) with eyes open, stability level of 8 with eyes closed, stability level of 6 (ie, less-stable support surface) with eyes open, and stability level of 6 with eyes closed. Postural-stability tasks were performed with and without auditory Stroop task. The anteroposterior stability index (APSI), mediolateral stability index (MLSI), and overall stability index (OSI) as measures of postural performance, as well as reaction time and error ratio as measures of cognitive performance, were recorded.

Results:

Dual-tasking effect on postural stability was not significantly different between the groups in 3 postural conditions. Only in level 6 with eyes open, for APSI and OSI, patients with ACL-R showed lower postural stability under the dual-task condition. However, patients showed poorer performance on both reaction time and error ratio in all postural conditions.

Conclusions:

The patients with ACL-R appeared to sacrifice their cognitive performance to optimize their performance on postural stability. This posture-first strategy was reflected by a more pronounced effect of dual tasking on the auditory Stroop task than the postural-stability task. In situations where maintenance of posture is challenging, giving priority to the postural task at the expense of cognitive performance can ensure safety from balance loss.