Affiliations: Department of Physical Therapy, Faculty of Allied Health Sciences, Kuwait University, Jabriyah, Kuwait | Department of Physical Therapy, School of Health and Rehabilitation Sciences, University of Pittsburgh, Pittsburgh, PA, USA | Department of Orthopaedic Surgery, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
Note:  Corresponding author: Fawzi F. Bouzubar, Department of Physical Therapy, Faculty of Allied Health Sciences, Kuwait University, P.O. Box 31470, Sulaibikhat 90805, Kuwait. Tel.: +965 2463 4865; Fax: +965 2463 3841; E-mail: Bouzubarf@hsc.edu.kw
Abstract: BACKGROUND: The quadriceps fatigue test is used to measure the progressive, exercise-induced, decline in the quadriceps maximal torque generating capacity over the course of time as an indicator of quadriceps fatigue. Reliability of this test has not been reported. PURPOSES: To determine: (1) test-retest reliability of the quadriceps fatigue test and (2) the relationship between quadriceps activation failure (QAF) and the quadriceps fatigue. METHODS: Nineteen volunteers with no history of knee impairments participated in two testing sessions. The quadriceps fatigue test was performed using repeated isometric quadriceps contractions at 50% of maximum voluntary isometric contraction (MVIC) torque. MAIN RESULTS: The quadriceps fatigue test demonstrated good test-retest reliability (ICC's of 0.92 (95% CI = 0.81 to 0.96) for the MVIC rate of decline at 5 minutes and 0.89 (95% CI = 0.75 to 0.95) for the MVIC rate of decline at total time. The results indicate that the quadriceps fatigue was due to “central fatigue”. Increased rate of decline of MVIC torque (i.e., more fatigue) was associated with higher magnitude of QAF (r = 0.52). CONCLUSION: In healthy individuals, the quadriceps fatigue test demonstrated good test-retest reliability. Quadriceps activation failure may play an important role on quadriceps fatigue mechanisms.