Background: Oral contraceptives are common among female athletes. Still, its effects on athletic performance are poorly investigated. Research in the area has increased in recent years. However, the study qualities and designs are often insufficient and with small sample sizes. Women are currently underrepresented in sport research, and to recruit more women in future studies and to facilitate female athletes’ choices about contraceptives, the impact of oral contraceptives on performance must be better understood. Aim: The aim was to investigate whether monophasic, combined oral contraceptive phases affected maximal muscle strength, anaerobic performance and the corresponding blood lactate response, or perceived mental and physical energy level among young women. Method: The study used a cross-over design where six participants were tested on two occasions. The participants were healthy women between 18 and 29 years old who had beenusing monophasic combined oral contraceptives for at least three months prior to the study. No criteria for training level was set. The Isometric mid-thigh pull (N) was used as an indicator ofmaximal muscle strength; and the Wingate anaerobic test (W) measured anaerobic performance and power with corresponding blood lactate levels (mmol/L) measured at 0, 3 and 5 minutes after termination of the test. The participants rated their current physical and mental energy level on both test occasions using a visual analog scale (0-10). Statistical analyses were madeusing Wilcoxon signed-ranked test. Results: Nine participants were recruited, of which six performed tests on both occasions. The participants had a mean (SD) age of 22.3 (1.8) years, a BMI of 23.3 (2.6) and all reached WHO’sphysical activity recommendations. No statistically significant differences in muscle strengthor anaerobic performance were found regarding peak force (p=0.60), peak power (p=0.35) oraverage power (p=0.60) between oral contraceptive phases. Neither were there any differencesin the blood lactate response to the Wingate test directly after (p=0.92), 3 minutes after (p=0.17) or 5 minutes after (p=0.60) the test. No differences in perceived mental energy level (p=0.35)or perceived physical energy level (p=0.17) between oral contraceptive phases were evident. Conclusion: Oral contraceptive phases did not affect maximal muscle strength, anaerobicperformance, blood lactate response or perceived mental or physical energy levels. Accordingly, there is no need to adapt training to oral contraceptive phases and women can berecruited in future research without consideration of oral contraceptive phases.