Context: Athletes are often examined for return to sports using a functional-testing algorithm. No research has determined whether a closed kinetic chain (CKC) isokinetic testing bout influences the reliability of functional tests. Objective: To determine whether a concentric CKC isokinetic test bout alters test–retest reliability of lower extremity functional testing. Design: Subjects participated in velocity-spectrum CKC isokinetic bouts on 2 days 1 week apart. Setting: Hospital-based clinic. Participants: 28 normal subjects (mean age 26.7 years, height 27.2 cm, weight 75.8 kg). Analysis and Results: Means and SDs were determined. Intraclass correlation coefficients were used to calculate test–retest reliability and between days 1 and 2 ranged from .91 to .98. Conclusions: Even after a CKC isokinetic test bout, test–retest reliability of functional tests is very high. Future research should determine test–retest reliability of functional tests for patients with lower extremity pathology.