Nastaran Ghotbi - Department of Physical Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.
Mohsen Bayat - Department of Physical Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.
Kazem Malmir - Department of Physical Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.
Shohreh Jalaei - Department of Physical Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.

Objectives: Lower extremity muscles are critical for maintaining dynamic balance and athletic performance. Fatigue of these muscles may affect dynamic balance. It is unclear whether fatigue in a particular muscle group can affect dynamic balance more than that in other groups. This study was conducted to evaluate and compare the effects of fatigue in ۵ muscle groups on dynamic balance in volleyball players. Methods: Fifteen healthy male volleyball players separately performed the Star Excursion Balance Test before and immediately after the occurrence of fatigue of ankle Plantar Flexor (PF), knee extensor, knee flexor, hip abductor, and hip adductor muscles. Composite reach distance and distance in anterior, posteromedial, and posterolateral directions were recorded, accordingly. Results: Repeated-measures Analysis of Variance (ANOVA) data indicated that fatigue of all muscle groups significantly decreased the mean score of composite (P<۰.۰۰۱). Anterior, posteromedial, and posterolateral distance scores decreased following muscle fatigue of knee extensors and ankle PFs (P<۰.۰۵). Discussion: This study suggested that regarding composite reach score, fatigue of ankle, knee, and hip muscles similarly decreased dynamic balance. However, evaluating three main directions revealed that knee extensors and ankle PFs muscles fatigue presented more prominent effects on the explored volleyball players’ balance, compared to the other muscles.

Muscular fatigue, Dynamic balance, Star Excursion Balance Test (SEBT), Volleyball, Lower extremity