Sex differences have been a topic of interest in exercise physiology as of late, especially the possibility of a sex-dependent fatigue mechanism. Signal complexity has the potential to provide a better picture of fatigue by examining the behavior of a signal produced throughout a fatiguing task. Complexity measures the self-similarity and regularity of a signal and is associated with a system’s ability to respond to a change in condition. PURPOSE: To determine if there are sex differences in variability and complexity of a force signal before and/or after maximal and or/submaximal exercise. METHODS: 16 healthy untrained individuals (9 females, 7 males) completed a maximal and submaximal isometric resistance exercise test using a handmade dynamometer. The maximal exercise test consisted of a 5-minute all-out test with 30 maximal effort isometric knee extensions at a 60% duty cycle (6s contraction, 4s rest). The submaximal exercise consisted of a submaximal test performed at 50% of their maximal voluntary contraction until task failure at a 60% duty cycle. Complexity and variability measures were calculated from the first and last three contractions. Performance measures included pre and post MVC, blood lactate, rating of perceived exertion (RPE), Time-to-Exhaustion (TTE), and force decrement. RESULTS: There were significant sex differences found in complexity and performance measures. Males experienced greater fatigue and levels of complexity after maximal and submaximal exercise. CONCLUSION: Further research is needed to determine the significance and applicability of complexity measures in exercise physiology. However, it appears low complexity in females is associated with increased fatigue resistance in a healthy untrained population after maximal and submaximal isometric resistant exercise.