Training with your cycle: how to use your running diagnostic

Why your cycle belongs in the plan

On average your cycle changes your performance only a little, but how you feel often a lot. That's why we don't steer training by a rigid calendar, but by phase and feel: hard sessions where you feel strong, more recovery where your body needs it. Blackroll calls this “training with your body, not against it”.

Research supports exactly this approach. A large review of 78 studies finds only a small drop in performance during the period and therefore recommends steering training individually, by your own response¹. At the same time, symptoms are common: of 6812 female athletes surveyed through the Strava app, 86 % knew fatigue and 84 % abdominal cramps during their cycle; the more symptoms, the more often they changed their training².

For your diagnostic with Adactiv Diagnostics this means: your Critical Speed and your zones hold for the whole cycle. What you adapt by phase is the day for hard sessions, the volume of single days and recovery. The next sections show how.

The phases at a glance

A cycle usually lasts 21 to 35 days and starts on the first day of your period. The days below apply to a 28-day cycle; with a longer or shorter cycle it is mainly the follicular phase that shifts.

The split follows the guideline by Swiss Olympic and the Swiss Football Association³ and the Blackroll article on cycle-based training⁴. How strongly you feel each phase is very individual. That's why it pays to note your period, energy and how training feels for two to three cycles.

Test and retest: when to test?

Test on a good day and, if you can, do the retest in the same cycle phase as the first test. Your Critical Speed depends on threshold and VO2max, and on average both stay the same across the cycle⁵. So you don't need to recalculate your zones for each phase; a maximal test, however, reacts to how you feel on the day and to symptoms.

• Don't test on days with strong symptoms, for example on the first or second day of your period. That is where performance is most likely to be slightly lower on average¹.
• Retest in the same phase. Your report shows a real change in CS from about 2 % (likely) or 4 % (clear). The same conditions, in your cycle too, keep the comparison clean.
• Move the test week if needed. If the test week at the end of your block falls on your period, run the two tests a few days later. There are 2 to 3 days between the two runs anyway.
• Test cool in the luteal phase. In the second half of your cycle your body temperature is higher, and in heat your endurance drops a little. Test in the morning or in cool weather.
• Note your cycle day. Write down the cycle day for every test. Over time you'll see whether a difference is linked to the phase.

How to adapt your plan

Your weekly volume stays the same; what you move are the hard sessions and the recovery within the week. Put the hard sessions in the first half of your cycle where you can, and more recovery in the days before and during your period if you need it. Blackroll recommends the same⁴.

Three rules make this easy in everyday life:

• Swap, don't skip. Swap a hard session with an easy day of the same week. Keep at least 48 hours between two hard sessions, as in the plan.
• Put the recovery week on your cycle. The plan in your report has a recovery week every 4th week (every 3rd if you go cautiously) with about a quarter less volume. If your cycle is regular, put that week on the days before and at the start of your period.
• Feel before calendar. If you feel strong during your period, train as planned. Top performances are possible in every phase.

On strength: in one study, 20 women trained one leg mainly in the follicular phase and the other mainly in the luteal phase for three cycles. The leg trained in the follicular phase got stronger and its muscle thicker⁶. A review comes to the same conclusion but calls the evidence preliminary⁷.

Heart rate, heat and nutrition

In the second half of your cycle you run with a higher body temperature: it is already higher before training and stays higher afterwards⁸. Heart rate and sweat rate during training hardly change on average. In heat, however, endurance drops measurably in the mid-luteal phase⁵.

• Heart rate zones stay valid. They come from your HRmax, and your heart rate in training hardly changes across the cycle on average. If your heart rate is higher than usual at the same pace, run slower: on easy runs heart rate then takes priority, as the report says for heat and hills.
• Prepare for heat. Run early in the day, drink more and start long runs more calmly. Swiss Olympic recommends extra salt in the luteal phase from 28 °C³.
• A little more energy before your period. Blackroll puts the extra energy need in the late luteal phase at 5 to 10 %, about 100 to 200 kcal a day⁴. Eat enough carbohydrate before long runs and hard sessions.
• Keep an eye on iron. Heavy periods are common among female runners: 36 % of 1073 runners surveyed at the London Marathon reported them, and they were linked to anaemia. Only 22 % had sought medical advice for it⁹. If you bleed heavily or are often tired, have a doctor check your iron levels.

On the bike

The same applies to female cyclists, just with watts instead of pace. In the Adactiv Diagnostics cycling report, Critical Power and power zones stay valid across the cycle, because VO2max and threshold are stable.

• Test and retest as for running: on a good day, the retest in the same phase and with the same prior load.
• Keep cool on the trainer. Indoors it gets too warm faster in the luteal phase. A fan, a cool room and enough to drink keep the watts stable.
• Watts stay the target. If your heart rate rises at the same power, that is normal in heat. Ride long rides in the heat a little lower in the zone.
• The bike as an alternative. Blackroll names easy cycling as a gentle option during your period⁴. For runners, an easy ride on those days can replace an easy run.

The pill, an irregular cycle and warning signs

Without a natural cycle you steer your training by symptoms instead of phases. If your period stops, that is a reason to see a doctor, not a sign of good training.

• On the pill your hormones are more even. Performance is the same across the pill cycle, including the pill break, and at most marginally lower than in women not on the pill¹⁰. If you notice symptoms during the break, the same rules apply as for your period.
• Irregular cycle: Note your period, energy and how training feels anyway. After a few months you'll see whether a pattern emerges.
• Period stops: If it stays away for three months or longer, have it checked by a gynaecologist. In female athletes a common cause is taking in too little energy for their training¹¹.
• Severe pain or very heavy bleeding that regularly keeps you from training should also be seen by a doctor.

In short

• For two to three cycles, note your period, energy and how training feels.
• Put the hardest sessions in the first half of your cycle when the week allows.
• With symptoms, swap hard and easy days within the same week; the weekly volume stays.
• Put your plan's recovery week on the days before and at the start of your period.
• Test on a good day and do the retest in the same phase.
• In heat in the second half of your cycle: run slower, drink more, heart rate before pace.
• If your period stops or you bleed heavily: see a doctor.

References

1. McNulty et al.: The effects of menstrual cycle phase on exercise performance in eumenorrheic women. Sports Medicine 50, 2020.
2. Bruinvels et al.: Prevalence and frequency of menstrual cycle symptoms are associated with availability to train and compete. British Journal of Sports Medicine 55, 2021.
3. Mél Pauli and Medical Staff SFV: Zyklusorientiertes Training: Good Practice SFV-ASF. Swiss Olympic, 2023.
4. Victorine Kulier: Cycle-Based Training: How to Optimize Your Performance. Blackroll, 2024 (updated 2026).
5. Janse de Jonge: Effects of the menstrual cycle on exercise performance. Sports Medicine 33, 2003.
6. Sung et al.: Effects of follicular versus luteal phase-based strength training in young women. SpringerPlus 3, 2014.
7. Kissow et al.: Effects of follicular and luteal phase-based menstrual cycle resistance training on muscle strength and mass. Sports Medicine 52, 2022.
8. Giersch et al.: Menstrual cycle and thermoregulation during exercise in the heat. Journal of Science and Medicine in Sport 23, 2020.
9. Bruinvels et al.: The prevalence and impact of heavy menstrual bleeding in elite and non-elite athletes. PLoS ONE 11, 2016.
10. Elliott-Sale et al.: The effects of oral contraceptives on exercise performance in women. Sports Medicine 50, 2020.
11. Mountjoy et al.: 2023 IOC consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine 57, 2023.