How Your Menstrual Cycle Impacts Biometrics (and Why It Matters for Your Training)

When it comes to optimizing your training and recovery, biometrics are one of the most powerful tools you can use. But if your body follows a monthly hormonal cycle, your biometrics—especially metrics like HRV (heart rate variability), resting heart rate, and recovery status—aren’t just about your workouts. They’re directly impacted by where you are in your menstrual cycle.

This isn’t a glitch in the system—it’s meaningful data. When you understand what your body is doing hormonally, those shifts in your biometric trends stop being confusing and start becoming a guide. At Alter, we help you interpret those changes and adjust your training accordingly, so you’re not working against your physiology—you’re working with it. And that leads to smarter recovery, more effective training, and sustainable progress.

Let’s break down how the menstrual cycle affects your biometrics, what to expect in each phase, and how understanding these patterns can dramatically reshape your fitness, recovery, and long-term results.

The Power of Biometrics: A Quick Refresher

Biometrics are measurable data points that give you insight into how your body is functioning day to day. With the Alter wearable, you’re tracking key signals like:

• Heart rate variability (HRV)

• Resting heart rate (RHR)

• Sleep quality

• Activity levels

• Recovery status

These are influenced by training intensity, stress, sleep, nutrition, and—importantly—your hormonal fluctuations throughout the menstrual cycle.

Understanding the Four Phases of the Menstrual Cycle

The menstrual cycle is a complex and dynamic process driven by hormonal fluctuations that influence nearly every system in the body. From strength and recovery to mood and energy levels, each phase presents different challenges and opportunities. While often simplified into two phases (follicular and luteal), the full cycle includes four distinct stages:

1. Menstrual Phase (Days 1–5)

Hormone levels (estrogen and progesterone) are at their lowest, and the uterine lining is shed. This often comes with reduced energy, cramps, and fatigue. HRV may dip slightly and resting heart rate may rise.

What to Do:

• Focus on light-to-moderate movement like walking, stretching, yoga, or low-load strength work.

• Avoid high-intensity sessions if cramping or fatigue is severe.

What to Eat:

• Prioritize iron-rich foods (e.g., spinach, red meat, lentils) to offset blood loss.

• Include anti-inflammatory options like turmeric, ginger, and omega-3s to ease discomfort.

2. Follicular Phase (Days 6–14)

Estrogen rises steadily, improving mood, motivation, energy, and physical capacity. Your HRV often increases and RHR lowers—this is your body’s go time.

What to Do:

• Lean into heavier lifts, endurance work, HIIT, or technical training.

• This is your prime window for strength and performance gains.

What to Eat:

• Prioritize protein-rich meals to support muscle building.

• Add complex carbohydrates to fuel high-intensity sessions and boost recovery.

3. Ovulation Phase (Around Day 14)

Estrogen peaks, LH surges, and testosterone sees a slight rise. Many feel their strongest here—power output, mood, and coordination are at their highest. However, joint laxity can increase, raising injury risk.

What to Do:

• Use this time to hit peak performance sessions, PR attempts, or technical lifts.

• Warm up thoroughly and focus on joint stability and good form.

What to Eat:

• Maintain balanced meals with protein, healthy fats, and carbohydrates.

• Hydrate well, especially if training intensity increases.

4. Luteal Phase (Days 15–28)

Progesterone dominates while estrogen tapers. PMS symptoms like bloating, irritability, and low energy may appear. HRV often drops and RHR increases, and recovery can take longer as your system begins working harder.

What to Do:

• Shift toward moderate cardio, mobility, or circuit-style strength with lighter loads.

• As PMS symptoms worsen, add in restorative practices like yoga or breathwork.

What to Eat:

• Add magnesium-rich foods (e.g., dark chocolate, pumpkin seeds) to ease bloating and mood swings.

• Emphasize complex carbs and electrolyte balance to support energy and hydration.

Why HRV Drops in the Second Half of Your Cycle

Many individuals notice a drop in HRV and an increase in resting heart rate during the luteal phase. This is expected. After ovulation, progesterone rises, increasing your core workload and slightly suppressing parasympathetic tone (rest and recovery). Since HRV reflects nervous system balance, this hormonal change shows up as reduced variability.

This doesn’t mean you’re doing something wrong—it means your body is asking for a different approach. When recovery slows and sleep quality dips, your training needs to adapt. That’s where the Alter wearable and our Readiness Score become game changers. Your sessions auto-adjust based on your data, nudging you toward a Work-in when your system needs recovery-focused movement instead of intensity.

Key Considerations for Training with a Menstrual Cycle

To get the most out of your training, understanding how your cycle affects your body is just the start. Here’s how to level up:

• Track Your Cycle: Leverage the Alter wearable to monitor patterns and anticipate energy shifts.

• Listen to Your Body: Adapt sessions based on real-time data like sleep, HRV, and mood.

• Support Recovery in the Luteal Phase: Metabolic demands are higher, so recovery may take longer. This is an ideal time to personalize training and recovery.

• Mind Your Mindset: PMS can affect motivation—hybrid sessions (e.g., 20 min strength + 10 min yoga) can support consistency without burnout.

Patterns, Not Problems

If you notice consistent changes in HRV, sleep, or energy throughout your cycle, that’s not a setback—it’s a pattern. Tracking these fluctuations alongside your cycle helps you anticipate your best training windows and dial back when your body needs support. That level of awareness builds consistency and confidence over time.

Progress Without Guesswork

The biggest myth in training? That you should feel the same every day. That’s just not realistic, especially for anyone with a menstrual cycle. Hormonal fluctuations impact recovery, cravings, focus, mood, and performance.

By syncing your training with your biometrics and cycle, you remove the guesswork. You stop forcing intensity and start building rhythm—one that’s aligned with your body’s needs and your long-term goals.

Built to Work With You

At Alter, we’ve built our entire system to support this approach. Your biometrics aren’t just numbers—they’re signals. Your session recommendations aren’t just workouts—they’re aligned with where your body is today. And your results aren’t just possible—they’re sustainable.

You don’t need to train through burnout or guess your way to progress. You need real data, flexible programming, and a system that evolves with you.

That’s not just personalization—it’s performance with purpose.