This study examined quadriceps fernoris (QF) muscle strength, the level of QF muscle inhibition (MI) and the kinetics of cycling in 11 subjects post-anterior cruciate Ligament (ACL) reconstruction and 7 controls. Isokinetic knee extension (90% and 240°/s), isometric knee extension, MI (twitch interpolation) and anterior knee joint laxity (KT 2000) were measured. For the cychg test, pedal forces were measured in the sagittai plane, and 3-dimensional leg kinematics were filmed while the subjects pedaled at 60 RPM against a load of 150 W. Compared to the controls. the ACL subjects had significant operated-thigh QF muscle weakness, less MI of the QF muscle, and the peak pedal z force occurred significantly later in the pedal revolution. Although operated-thigh QF muscle weakness was present, there was evidence that the muscle was not inhibited. Weakness of the QF muscle post-ACL reconstruction is likely multi-factorial, and thus presents a complicated rehabilitation problem.