
Fatigue is one factor that affects lower limb dynamic joint stability during athletic tasks. Research has reported greater lower-extremity injuries because playing time and fatigue are increased in sports such as rugby, soccer, and field hockey. This can affect athletic performance. It has been thought that reduced muscle force, less coordination, delayed neuromuscular activation, increased knee shear forces and moments, and impaired joint stability are key factors that are responsible for lower-extremity injury rates during fatigued conditions. The specific fatigue-induced mechanisms thought to be responsible for increased knee injury, especially anterior cruciate ligament (ACL) tears, remain unknown for both sexes. Fatigue involves both peripheral and central nervous system factors, which are difficult to recreate in a laboratory (Ortiz 2012). Several studies have looked at the effects of fatigue with varied fatigue protocols. Less knee flexion , decreased vertical jump height, increased electromyographic (EMG) activity of quadriceps and hamstrings, and impaired balance have been found by some investigators after the onset of fatigue (Ortiz 2012). Other studies have reported no differences in biomechanical and performance measures between non fatigued and fatigued conditions. The effects of fatigue not only could increase the risk for injury but also might impair jumping performance and athletic execution by decreasing knee power, jump height, and muscle work.