Cycling counts as an active physical activity of an anaerobic nature - especially if you’re going pretty fast.

The most effective time to hit intense workouts of an anaerobic nature is during the follicular phase, which typically lasts approximately 14 days, starting from the 1st day of the menstruation cycle. So, you can go cycling at any time anywhere.

During your period, you should be careful with regard to cramping and the hygiene products you’re using. It may feel a little uncomfortable to use pads when you cycle, so try tampons or menstrual cups instead.

During menstruation, estrogen starts to gradually increase by the middle of your cycle, and body temperature stays at the same level.

Of course, it may feel uncomfortable to cycle during the heavy flow stage and if you have cramps. If this is the case, take a break and do yoga instead. However, it’s time to hit the bike right after your period. Your body enters a state of renewal this time and gets ready for possible conception. Metabolism is accelerated, insulin sensitivity is increased and susceptibility to pain is decreased. You feel elevated and full of energy, and are able to endure more.

Don’t forget to eat healthier carbs at this time of your cycle to maintain the activity - nutrition balance.

Sources:

Cycling time trial performance during different phases of the menstrual cycle, ncbi.nlm.nih.gov

Bicycling and women's sexual health, womenshealth.northwestern.edu