How to work out when you're tired before your period

Lack of energy before your period is common: in a survey of 6,812 women who exercise, 86.2% listed tiredness as a cycle symptom. Keep lifting, but lighten those sessions: one fewer set per exercise at your usual weight, aiming one point lower on the 1-to-10 effort scale (RPE 7 instead of 8). If your energy drops a lot, do about half your sets at roughly 90% of your usual weight.

By the STRONG team · Updated October 2026

How common is fatigue before your period?

The survey was published in the British Journal of Sports Medicine in 2021 (several of the authors work for a company that makes a cycle-tracking app). It recruited exercising women through Strava, and none of them were on combined hormonal contraception. Tiredness came second on the list of symptoms. Only mood changes or anxiety were more common, at 90.6%, and stomach cramps (84.2%) and breast pain or tenderness (83.1%) were close behind.

Symptoms also got in the way of training: the heavier a woman's symptoms were, the higher her odds of missing or changing a session.

What the research says about cycle phase and strength

We plan around symptoms, not cycle phases, because on average the phase makes at most a trivial difference to how you perform on a given day. The largest meta-analysis on the question (78 studies, 1,193 women) found that performance "might be trivially reduced" during menstruation, rated the evidence low quality, and concluded that general guidelines across the cycle can't be formed. A 2023 umbrella review, a review of the existing reviews, pointed out that a plan built on a textbook 28-day cycle amounts to switching your training every two weeks, and it judged the two training studies behind phase-based lifting methodologically flawed. Our guide to cycle syncing and strength training goes through the studies on both sides.

Should you work out with PMS?

Say it's three days before your period, you didn't sleep well, and your first warm-up set of squats feels the way your last working set usually does. Train anyway, but make it a lighter day: do one fewer set of squats at your usual weight and keep the rest of the workout as planned. If your legs feel worst, you can turn the day into an upper-body session or take it off.

The studies on exercise and PMS lean positive, but they're weak. A 2020 meta-analysis in BJGP Open covered 15 randomized trials with 717 women. Its main analysis pooled 7 of those trials (265 women) and found lower overall PMS symptom scores in the women who exercised. The authors still wrote that "some uncertainty remains," because 87% of the trials were at high risk of bias and the results varied widely from study to study. The UK's National Health Service (NHS) lists regular exercise among the things to try for PMS.

How much lighter should a PMS workout be?

RPE (rate of perceived exertion) is a 1-to-10 effort scale, where 10 means you couldn't have done another rep. STRONG uses two levels, the lighter day and the very light day. In the table below, a normal session is 4 sets of 8 to 10 squats at 40 kg (about 88 lb).

Because a lighter day keeps the weight on the bar, you keep practicing with the load you've built up through progressive overload, and the missing set is what makes the session easier. A very light day cuts sets and weight together, so it works like a one-day version of a deload week.

You don't need an app for any of this. If you train from a notebook, pick the column that matches your energy and do every exercise you planned with that column's sets and weight. When your warm-up sets feel heavier than they did last week, switch to a lighter day right there in the gym. Write down which column you used each day, and after two or three cycles you'll know which days to plan around. For the bleeding days themselves, see working out on your period.

This is how STRONG plans it

The cycle feature stays off until you turn it on.

Once it's on, you answer three questions:

1. How much does your energy drop? You pick "Hardly," "Noticeably" or "A lot." "Noticeably" gives you 2 lighter days, and "A lot" gives you 3 very light days.
2. When does it drop? The choices are "The days before it starts," "The first days of bleeding" or "Both." With "Both," you get that many days before your period and again in its first days, up to 10 in a row.
3. Does it last longer than a week? If you say yes, the count goes up to 5 lighter days or 7 very light days.

Periods drift a day or two, so the planner also turns the day on either side of that stretch into a lighter day. When your hardest days first come up, the app asks how to plan them: "Lighter sessions," "Upper body only" (lower-body sessions move to other days) or "Rest" (the week is planned around them).

Say you answer "Noticeably," "The days before it starts" and no, and your next period is due on a Friday. Wednesday and Thursday become your 2 lighter days, and Tuesday and Friday are the buffer. Any session from Tuesday to Friday comes up as a lighter day, so your Romanian deadlifts stay at the same weight with one fewer set, even if the reps feel easy.

If you answered "Noticeably" or "A lot," the planner also places your deload week (the app calls it your easy week) around every predicted period: "The week before my period," "The week my period starts" or "Half and half." With fewer than 2 regular weeks since your last break, that week is a lighter week instead (one set fewer, same weights). You never get two easy weeks in a row, and if your cycles are very long, a deload comes automatically after 5 regular weeks. With "Hardly," you get no lighter days, but a deload that's due moves onto your period week.

Predictions need some history. STRONG doesn't predict anything until you've logged at least 2 cycles that differ by 10 days or less. From then on it uses the median of your last three cycle lengths (or of the ones you've logged so far), and the buffer widens to as much as 3 days if your cycle varies. Your cycle data (last period start, cycle length and energy answers) stays on your phone and is never uploaded. Until a prediction is possible, tap "My period started today" when it does, and the next days are planned lighter.

On any day, "Low energy today? Make it lighter" turns that session into a lighter one, and on a planned light day, "Feeling good? Train normally" gives you the full session back. You can change every answer in Settings, and your plan and reminders update at once. You can also delete your cycle data there; your training history stays.

When to see a doctor

We can help with the training side. If the tiredness worries you, ask a doctor about it. See one as well if your periods get more painful, heavier or irregular, if cramps keep you from your usual daily activities, or if you bleed between periods or after sex. Signs of heavy periods include needing to change a pad or tampon every 1 to 2 hours, periods that last more than 7 days, and avoiding activities like exercise because of your period. Get medical care right away if the pain is severe or worse than usual and pain relievers haven't helped.

The NHS lists doing too much exercise and sudden weight loss among the causes of missed periods. If your period stops or becomes irregular while you're training hard or eating less, see a doctor. The NHS says to see a doctor if you've missed 3 periods in a row, and the IOC links low energy availability (eating too little for your training load) to a syndrome of health problems called REDs, short for Relative Energy Deficiency in Sport.