Why the Menstrual Cycle Matters
Why the Menstrual Cycle Matters for Female Athletes. And What Happens When It Disappears...
by Meg Smith, PhD Researcher at Loughborough University and Female Athlete Health Consultant for AG-Insurance Soudal Women’s World Tour Cycling Team
For far too long there has been a narrative within sporting contexts that women are just ‘small men’ with their biology being considered a distraction rather than a performance factor. But a growing body of research and real‑world coaching and athlete experiences show that the menstrual cycle is not a barrier to performance, it’s a powerful source of insight into an athlete’s health, readiness, and resilience.
In female athletes, the menstrual cycle is a vital sign, just like heart rate or sleep quality. It reflects the complex interplay between hormonal health, energy availability, and physical stress. Understanding it and its unique patterns doesn’t just help athletes avoid health issues, it fundamentally improves performance.
Why the Menstrual Cycle Is Important for Female Athletes
The menstrual cycle is regulated by several female sex hormones, most importantly oestrogen and progesterone, which influence a wide range of physiological systems, including:
Energy metabolism: Hormones affect carbohydrate storage, fat metabolism, and insulin sensitivity.
Muscle function and recovery: They influence muscle strength, tendon stiffness, and muscle repair processes.
Bone health: Oestrogen plays a key role in maintaining bone density.
Thermoregulation and fluid balance: Hormonal shifts alter how the body handles heat and hydration.
Mood and cognition: Hormones impact motivation, fatigue perception, and sleep quality.
Critically, the cycle is not static. Hormonal concentrations fluctuate throughout the phases of the menstrual cycle, meaning that an athlete’s physiology changes from week to week. When we understand these shifts and patterns, training and recovery can be optimised around them, not in spite of them.
For example, some athletes may naturally handle higher intensity training better in certain phases, while others might need more recovery or nutritional support in others. Tracking these patterns empowers athletes and coaches to personalise training, which is a key advantage in professional sport where we are constantly on the hunt for marginal gains.
Why Some Female Athletes Don’t Get a Period
One of the most common questions I’m asked as a coach, practitioner and researcher is: “Why have I stopped getting my period?” For athletes, the answer often lies in a condition known as Functional Hypothalamic Amenorrhoea, a downregulation of the female reproductive system driven by prolonged energy deficit and physiological stress.
When energy intake doesn’t match energy expenditure (often due to high training loads, insufficient calories, stress, or inadequate recovery), the body prioritises survival over reproduction. The brain’s hypothalamus reduces its signals to the reproductive system, leading to missed periods or complete amenorrhoea (no periods).
This isn’t just inconvenient, it’s a red flag. Absent periods are often one of the earliest clinical signs of Relative Energy Deficiency in Sport (REDs), a syndrome recognised by the IOC that describes impaired physiological function caused by energy deficiency. REDs affects not only menstrual function but also:
Bone health (increased fracture risk)
Immunity (higher illness rates)
Metabolism and thyroid function
Cardiovascular health
Psychological wellbeing
The absence of a period should never be considered “normal” or just an athletic side‑effect. It’s the body’s way of saying: There’s not enough energy to fuel both performance and fundamental biological processes.
How Understanding Your Cycle Helps You Perform Better
Tracking the menstrual cycle gives athletes (and coaches) valuable context for understanding training responses, recovery, and overall wellbeing.
Rather than prescribing training purely based on menstrual cycle phase, monitoring the cycle alongside training data (such HRV, RHR, perceived exertion, sleep and recovery) allows athletes to identify their own individual patterns. Hormonal fluctuations can influence fatigue, thermoregulation, recovery and perceived effort, but responses vary widely between individuals. This means a one-size-fits-all approach to cycle-based training is unlikely to be effective. Instead, consistent tracking helps athletes and coaches interpret fluctuations in performance more accurately and make informed adjustments when needed.
Cycle awareness is also important from a health perspective. Changes in menstrual patterns, including changes to cycle length, bleed pattern, missed or irregular periods, can be an early sign that energy intake is not matching the demands of training. Recognising these signals early allows athletes and practitioners to address issues such as low energy availability before they develop into more serious consequences associated with REDs.
Just as importantly, understanding the menstrual cycle gives athletes greater awareness and ownership of their bodies. Rather than viewing symptoms like fatigue or mood changes as random, they can be understood in context and managed more proactively.
The menstrual cycle is not a weakness, it’s a crucial indicator of athlete health and readiness. Ignoring it is no longer acceptable in modern sport science and coaching. Organisations like Project REDs are helping drive a shift toward recognising energy availability, menstrual function, and hormonal health as central components of athlete wellbeing and performance.
For female athletes, the message is simple: your menstrual cycle matters, and protecting the energy that supports it is essential for both health and performance."