The bilateral limb deficit (BLD) phenomenon is the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. A deficit occurs when the summed unilateral force is greater than the bilateral force. The BLD has been observed by a number of researchers in both upper and lower limbs, in isometric and in dynamic contractions. The underlying cause of the deficit remains unknown. One possible explanation is that the deficit occurs due to differences in antagonist muscle coactivation between unilateral and bilateral contractions. In order to examine this potential cause, this research examined torque and electromyography (EMG) during isometric bilateral and unilateral knee extension under three different joint angles (0°, 45°, and 90°) in a group of young, athletic males (n = 10, mean age of 24.5 ± 2.7 years, height = 180 ± 4.71 cm, and weight = 82.5 ± 17.8 kg). Torque and EMG data were collected from three superficial muscles of the quadriceps (vastus lateralis, vastus medialis, and rectus femoris) as well as two muscles of the antagonist hamstrings (biceps femoris and semitendinosus) during maximal isometric knee extensions. The BLD was only observed during the 45° contractions. Further examination of the data found that the antagonist muscle activity was similar during both bilateral and unilateral contractions suggesting that the deficit is not due to alterations in antagonist muscle patterns between unilateral and bilateral contractions.