Muscular co-activation is defined as opposing muscle activity (e.g. hamstring) when the main contracting muscle is active (e.g. quadriceps). This mechanism has been shown to stabilize joints and improve accuracy during voluntary movements. However, literary evidence suggests that muscular co-activation can speed up muscular fatigue and may be detrimental in people with joint-related injury or disease. In addition, some research has demonstrated that muscular co-activation increases during a fatiguing task. Previous studies show that strength training protocols can help reduce co-activation levels significantly. They also seem to suggest that reduction in opposing muscle activity occurs as a primary form of neuromuscular adaptation; this adaptation has been found to take place in the early stages of strength training as EMG (surface electromyography) and MVIC (maximal voluntary isometric contractions) increments aren’t directly proportional. However, very little is known about the effects that short-term training would have on co-activation patterns during fatigue tasks. The purpose of this study was to test if short-term training would produce a significant decrease in co-activation patterns during a fatigue task. 23 subjects (9 men, 14 women) were between the ages of 18 and were chosen based on selective criteria. The study comprised of 6 visits: one pre-test, followed by four training sessions and then a post-test. Subjects were randomized into one of three groups: strength training, endurance training, and control. For each testing session, subject’s EMG, MVIC and failure time at 50% effort were measured. Co-activation was measured over time during the fatigue task and compared at pre and post-test intervals. Subjects’ knee extensors and flexors were the target muscles of training and testing for this study. Data analysis was made via two-tailed paired T-tests and Matlab. The short-term training protocols used in this study did not produce significant change in isometric strength, endurance time, or muscle co-activation during an isometric fatigue task. Future areas of interest would include modification of training protocol intensity or duration."