We’ve Been Told To Work With Our Cycles — But The Science Isn’t So Simple
Maybe your period-tracking app says it's time for strength training.
A few days later, it might suggest taking it easier. That's the basic idea behind cycle syncing: changing your workouts, food, and recovery based on where you are in your menstrual cycle.
It sounds personalized, especially when an app is already tracking your period. But there's a difference between noticing patterns in your body and knowing exactly what's happening inside it.
A recent BMJ analysis1 looked at what we actually know about cycle syncing and digital menstrual tracking.
About the review
The authors reviewed research on digital menstrual tracking and cycle syncing, including whether these practices improve health, well-being, or physical performance.
Many period-tracking apps now do more than predict your next period. They estimate which phase of your cycle you're in, then use that information to suggest changes to your workouts, nutrition, or other habits.
Most apps don't measure your hormones or confirm when you ovulate. Instead, they usually estimate your cycle phase by counting forward from the first day of your last period.
Even if your periods are regular, ovulation can happen at different times from one cycle to the next. That means the phase your app gives you may not match what's actually happening in your body.
So, does your cycle need to dictate your routine?
The analysis found no convincing evidence that your menstrual cycle consistently changes physical performance, injury risk, or health enough to support broad cycle-syncing rules.
For example, research in elite rugby players found little evidence that cycle phase affected performance across several physical tests. Research on whether certain cycle phases raise ACL injury risk has been mixed, while studies on changing nutrition based on cycle phase are still inconclusive.
That doesn't mean your cycle can't affect how you feel. You might notice changes in energy, appetite, mood, or cramps throughout the month, and those patterns can be useful.
The bigger leap is assuming everyone needs to follow the same rules at each stage of the cycle.
When tracking becomes a set of rules
Tracking your period and symptoms can help you spot changes worth discussing with a healthcare provider.
The issue is when an estimated cycle phase starts telling you what you should or shouldn't do.
Some cycle-syncing advice recommends sticking to lower-intensity activities such as walking or yoga during large parts of the cycle.
The analysis notes that this can go against general physical activity guidance when there's no clear reason to scale back.
Cycle tracking also can't tell you what's causing irregular periods, severe pain, or other major changes. Conditions such as relative energy deficiency in sport and endometriosis need proper medical evaluation.
How to use cycle tracking without overthinking it
You don't have to ditch your period-tracking app. Just use it as a tool for noticing patterns, not as a rulebook.
- Look for your patterns: Track changes in symptoms, energy, or your period over time instead of automatically changing your routine based on an app's predicted phase.
- Keep the basics consistent: Regular movement, adequate nutrition, and enough recovery matter throughout your cycle.
- Pay attention to changes: If your periods become irregular, unusually painful, or noticeably different, talk with a healthcare provider rather than relying on an app to explain what's going on.
The takeaway
Your period app can help you spot patterns, but it can't tell you everything happening inside your body. Use the data as a clue, not a command.
