Interest in cycle-based workouts has increased significantly, largely due to the growth of femtech and social media. The concept suggests that the four phases of the menstrual cycle affect energy, strength, and recovery due to hormonal changes. However, the scientific backing is mixed. A December 2025 review confirmed estrogen's influence on metabolism and exercise performance, while a 2022 study showed that resistance training during the follicular phase led to greater strength gains. Conversely, a 2023 review indicated that the evidence for hormonal fluctuations affecting strength performance is still inconclusive, largely due to historical exclusion of women in exercise science research. Women are advised to track their cycles to identify personal patterns in energy and strength, with the first half of the cycle being optimal for intense workouts. The femtech market, including cycle-syncing apps, is rapidly expanding, indicating a growing interest in women's health and fitness. Upcoming research, such as the Karolinska IMPACT Trial, aims to further explore the efficacy of cycle-based training.