As a competitive freediver and instructor, I’ve spent many hours training myself and coaching others. One thing that frustrated me early on in my training was inconsistency. Some days felt effortless and rewarding, while other days i felt unable to achieve even my usual baseline. Does that sound familiar?

This variability can be due to factors like stress, fatigue, the time of day, or countless other things. As freedivers, it’s easy to fixate on chasing the “perfect” dive day. But what if we instead focused on understanding and embracing the natural rhythms of our bodies and minds.

One of the most insightful areas I’ve explored in my own training has been understanding the relationship between freediving and the menstrual cycle, in particular my CO2 tolerance. By learning to align my training with these changes, I’ve found more effective training strategies and greater self acceptance of the natural ups and downs of training.

A Quick Refresher on Your Menstrual Cycle

The menstrual cycle has four main phases, each marked by different hormonal changes that can influence both physical and mental states. Of course, everyone is different and you may experience these phases differently. But here are some common trends.

• Menstrual Phase (Period): This is the start of the cycle when the uterine lining is shed. Hormones like estrogen and progesterone are at their lowest. Energy and focus may begin to pick up in the later part of this phase.
• Follicular Phase: As the body prepares for ovulation, estrogen levels rise. Many people feel energised, clear headed, and strong during this phase.
• Ovulation Phase: Around the midpoint of the cycle, ovulation occurs. Estrogen peaks, and some people may notice changes in mood, energy, and even physical sensations.
• Luteal Phase: After ovulation, progesterone rises, which can lead to fatigue and mood instability.

Why Track Your CO2 Tolerance and Plan Training Around Your Cycle?

CO2 tolerance is your ability to handle rising levels of carbon dioxide during a breath hold. This ability can fluctuate throughout your cycle. Observing and planning your training with these different times can:

• Help you plan ahead: Anticipate times when your CO2 tolerance may be higher or lower and tailor your training accordingly.
• Maximize performance: Take advantage of high tolerance days for longer distances or PB attempts.
• Cultivate self kindness: Be patient and understanding with yourself on days when CO2 tolerance feels lower.
• Avoid negative mental associations: Prevent frustration or burnout by modifying training on challenging days, keeping your relationship with freediving positive.

While competitive freediving demands the adaptability to perform on any given day, leveraging the natural rhythms of your cycle can help avoid overtraining and reinforce a positive mindset.

My Personal Observations

In my own experience, CO2 tolerance shifts noticeably throughout my cycle. For example:

• During and shortly after my period, my CO2 tolerance tends to be at its best, breath holds feel easier and i feel more energetic. Around ovulation, I experience a significant dip in my CO2 tolerance, lasting a few days before gradually improving again.
• Other freedivers i have trained with notice their lowest CO2 tolerance in the days leading up to and during their period.

Remember we are all different, and finding out your own natural pattern is important. For me, knowing this pattern allows me to plan ahead. On lower tolerance days, I often focus on technique refinement, dive shorter/shallower distances with longer recoveries. Alternatively i might also use these sessions to practice mental relaxation techniques, embracing the challenge of managing stronger CO2 sensations and improve my mental game.

How to Track Your CO2 Tolerance

One of the most effective ways I’ve found to monitor CO2 tolerance is through a consistent pranayama box breathing practice.

Here’s how to get started:

• Set aside 10 minutes each morning: Do this as soon as you wake up, before eating or drinking anything.
• Choose a manageable breathing cycle: Start with a pranayama box breathing pattern that feels achievable to continue for 10 minutes. It should allow you to feel some CO2 build up but not to the point where you need to end the holds early. For example:
• If you’re just starting out try: Inhale for 5 seconds, hold for 10 seconds, exhale for 10 seconds, hold for 5 seconds
• If you have some more experience try: Inhale for 10 seconds, hold for 20 seconds, exhale for 20 seconds, hold for 10 seconds.
• Track your tolerance: Record how the practice feels each day. Is it easy, challenging, or somewhere in between?

After 1-3 months of consistent tracking, patterns will emerge. For me, this practice revealed some clear shifts in CO2 tolerance tied to my menstrual cycle, which became invaluable in planning my training.

A great app for pranayama breathing is the STAmina App

Practical Takeaways for Freedive Training

Once you’ve identified your CO2 tolerance patterns, you can:

• Maximise high tolerance days: Schedule longer breath-holds, more difficult CO2 tables, or PB attempts on days when you are more likely to have your best CO2 tolerance.
• Adapt on low tolerance days: Focus on technique, shallower/shorter distances, or surface swimming. Or use this time to strengthen your mental toolkit by practicing relaxation and mindset techniques through stronger CO2 feelings.
• Avoid overtraining: By choosing to rest or modify your approach when needed, you can help to avoiding frustration, nervous system burnout and negative associations with training.
• Prepare strategically for competition: It’s true that in competition, you must be ready to perform on any day, regardless of where you are in your cycle. However, knowing your typical patterns can help mentally prepare you for how the dive will feel on the day and simulate those more challenging conditions during training.

Final Thoughts

Understanding and embracing the connection between your menstrual cycle and CO2 tolerance isn’t about creating the perfect day for a dive. It’s about respecting the natural cycles of your body and using that knowledge to enhance your training. By doing so, you’ll not only improve your performance but also cultivate greater self compassion and resilience in the water.

Remember, freediving is as much about listening to your body and mind as it is about physical skill.

If you have any questions about freediving and the menstrual cycle or about freedive training in general, send me a message. Happy diving!