A new Swedish study has shed some light on when is best to work out during the menstrual cycle, suggesting that training during the first two weeks could be most beneficial for muscles.
How the menstrual cycle affects sports training is largely unexplored, but came under the spotlight recently when during the Rio 2016 Olympics, Chinese swimmer Fu Yuanhui admitted feeling tired during her performance due to starting her period the day previously.
With most sports research looking at men, despite the increasing number of women taking part in sports, Lisbeth Wikström-Frisén, a doctoral student at the Department of Community Medicine and Rehabilitation at the university and author of the dissertation, wanted to look at how women can optimize their training based upon the hormone cycle.
The small-scale study recruited 59 women, who participated in a four-month leg resistance training program.
One group underwent high frequency leg resistance training (five times per week) for the first two weeks of each cycle, while another group underwent the same training program but in the last two weeks of the cycle.
Wikström-Frisén also carried out a comparison between the women taking birth control pills and those not taking birth control.
The results showed that training in the first two weeks had a larger effect on muscular strength, power and muscle mass than training in the latter two weeks, suggesting that women could achieve better results from their workout without necessarily increasing the number of gym sessions, with Wikström-Frisén commenting that, "Since menstruation is a central part in everyday life for women and their training, we need to become better at taking this into account when optimiziing training."
Although the study showed no noticeable difference in those taking hormone-based birth control pills and those not on the pill, Wikström-Frisén also looked at the cortisol levels of a further 33 female participants for nine months, finding that although the results did depend on the season, women who took birth control pills generally had higher levels of the stress hormone.
"The varying levels of cortisol are of importance when optimizing training for women," commented Wikström-Frisén. "If we measure cortisol levels of women who are on the pill and find increased values, it could easily be interpreted as if they are overtrained, but that's not necessarily the case according to our research results."