Hormones shift across your cycle, and for a lot of runners, so does how a given pace or effort actually feels. Here's the general pattern — and why we're careful not to overclaim it for any one person.
Cycle length varies a lot person to person, so treat these as general patterns rather than a fixed calendar.
Hormone levels are at their lowest. Some runners feel flat or low-energy here; others feel completely normal — this is one of the most individual parts of the whole cycle.
If a run feels harder than usual around this time, it's not in your head. Easing intensity slightly, without abandoning the plan, is a reasonable default.
Rising estrogen through this window is linked, in a lot of the research, to better recovery and a higher tolerance for harder efforts.
Many runners find this a good window for their toughest sessions — intervals, tempo work — if their schedule allows shifting things around.
A short hormonal peak. Some runners notice a genuine performance high here; others notice nothing different at all — again, highly individual.
Ligament laxity may increase slightly around this window for some people, which is worth being mindful of if you're doing anything with sharp changes of direction.
Progesterone rises, and for many runners this brings a small uptick in resting heart rate and body temperature — which can make an easy run feel like it's costing a bit more than usual, even at an unchanged pace.
This is a big part of why we look at heart rate relative to pace, not pace alone, when something feels harder than it should.
Cycle length varies enough between individuals that a generic 28-day calendar is wrong for most people. Rather than guess which phase you're likely in and risk being confidently wrong about something this personal, your recaps only ever report what's actually been logged — days since your last period, for example — not an estimated phase.
As more of your own cycle history builds up, phase estimates based on your actual patterns (not a population average) become more realistic — something we're looking at adding down the line.
This is general educational information about common patterns, not medical advice, and not a prediction about how any single day will feel for you. Individual variation is significant. If you have concerns about your cycle or how it's affecting your training, please talk to a doctor.