Irregular menstrual cycles are often dismissed as part of being active, but Irregular Menstrual Cycles Are a Warning Sign, Not a Normal Part of Training. For many women in sport, changes in cycle length or regularity are seen as inconvenient rather than concerning. But irregular menstrual cycles are one of the clearest indicators that your body is under stress. When your cycle changes, your body is signalling that something is not right.
A healthy menstrual cycle is a marker of wellbeing and performance. It reflects how well you are fuelling, recovering, adapting and managing the demands of life and training. Ignoring these early signs can lead to greater health and performance issues later.
What a Healthy Menstrual Cycle Should Look Like
A normal menstrual cycle typically ranges from 24 to 35 days¹. Some variability is normal, but large swings from month to month are not. A healthy cycle includes clear hormonal shifts, regular ovulation and predictable patterns.
Ovulation is a key marker of menstrual health. It reflects a functioning hypothalamic–pituitary–ovarian axis. Ovulation supports bone health, metabolism, mood and long term wellbeing².
Bleeding should be manageable. Pain should not interrupt daily life. Heavy or very painful periods may indicate other medical conditions, but cycle timing should remain predictable unless something is affecting hormonal regulation.
Understanding Menstrual Irregularities
Cycle disruptions can present in different ways. The pattern offers clues about underlying causes.
Oligomenorrhoea:
Cycles longer than 35 days.
Secondary amenorrhoea:
Lack of a period for three months or more after previously regular cycles.
Primary amenorrhoea:
No period by age 15 or 16.
Anovulatory cycles:
Bleeding occurs, but ovulation does not. This means hormonal balance is disrupted even if a bleed appears normal.
Short cycles:
Under 24 days.
Long cycles:
Over 35 days.
All of these can be symptoms of hormonal disruption. Irregular menstrual cycles should never be normalised.
Why Irregular Cycles Should Never Be Ignored
The menstrual cycle is a monthly health report. It reflects how the brain communicates with the ovaries. When the cycle becomes irregular, the hormonal system is not functioning optimally.
Disruptions can affect bone density, and increase the risk of stress fractures³. Over time, irregular cycles can also impact metabolic health, mood, immunity and performance. Athletes may notice fatigue, poor recovery and stagnation in training.
Ignoring irregularities delays treatment. Early intervention protects long term health and performance.
Common Causes of Irregular Menstrual Cycles
Irregular menstrual cycles can arise from multiple factors. Some relate to energy intake. Others relate to stress, training load or medical conditions.
Low Energy Availability (LEA)
LEA occurs when energy intake does not meet the energy needs of training and daily living. Chronic LEA suppresses reproductive hormones, and ovulation may stop⁴. This can lead to functional hypothalamic amenorrhoea.
RED-S
Relative Energy Deficiency in Sport is the wider syndrome linked to LEA. It can impact bone health, immunity, endocrine function, metabolism, digestion and mental health⁵. Cycle disruption is a recognised symptom.
High training loads
Heavy or frequent training without adequate fuelling or recovery increases physiological stress. In many cases this interacts with LEA. Training alone rarely causes cycle disruption without some form of energy mismatch⁵.
Psychological stress
Life stress can disrupt the hypothalamus. Moving house, exams, bereavement, or relationship strain may alter cycle regularity⁶.
Low carbohydrate availability
Even if total calorie intake seems adequate, low carbohydrate intake can alter leptin, insulin and thyroid hormones. This affects ovulation⁷.
Rapid weight loss
Significant or sudden body composition changes increase metabolic stress and can suppress reproductive hormones⁸.
Medical causes
Thyroid dysfunction, PCOS, illness, inflammation or perimenopause may also contribute. These require medical assessment⁹.
Low Energy Availability and RED-S: A Major Cause in Athletes
LEA is one of the most common causes of irregular menstrual cycles in active women. When fuel intake is too low, the body prioritises survival over reproduction.
The hypothalamus reduces the signals that trigger ovulation. Over time this leads to irregular cycles or amenorrhoea. Many women do not realise they are under fuelling. They may eat “healthy” foods but simply not enough to match their training load.
Common signs of LEA include fatigue, poor sleep, Irritable Bowel Syndrome (IBS), low mood, reduced performance, increased illness and frequent injuries⁴.
How Hormonal Contraception Can Mask Cycle Disruption
Hormonal contraception often changes bleeding patterns. This makes it harder to assess menstrual health.
The bleed experienced on the combined pill is a withdrawal bleed. It does not confirm ovulation or natural hormonal rhythms¹⁰. Long acting methods such as the implant or injection may stop bleeding entirely. This makes it difficult to detect cycle disruption.
This means you can have irregular menstrual cycles underneath, but the contraceptive pattern masks them.
What to Look For If You Use Hormonal Contraception
If you use hormonal contraception, you need to monitor other markers of health. Even without a natural cycle, the body gives early signs of stress.
Look for changes in:
Energy
Mood
Libido
Sleep
IBS
Recovery
Appetite
Performance
Injury frequency
Urinary Incontinence
These can indicate hormonal disruption even when menstrual bleeding is not present or predictable¹⁰.
Identifying Irregular Cycles if You Are Not on Contraception
If you are not using hormonal contraception, cycle tracking offers valuable insight. Track the length of each cycle, symptoms and ovulation signs.
Look for consistent patterns. A cycle that is very short, very long or unpredictable requires attention. A missed period for three months should be investigated².
Tracking helps you identify changes early and supports discussions with healthcare professionals.
When to Seek Support and Which Tests May Help
Seek support if you experience:
Irregular menstrual cycles
Periods longer than 35 days
Cycles shorter than 24 days
No period for three months
Symptoms of LEA or RED-S
Frequent injuries or reduced performance
Useful tests include:
Hormone panels
Thyroid function
Cholesterol
Vitamin D
Iron status
Bone health assessments
A GP, Sports Physician, endocrinologist or registered performance nutritionist can support you.
Nutrition and Lifestyle Actions to Restore Cycle Regularity
Restoring regular cycles often requires increasing energy availability. Eat more across the day. Support long sessions with carbohydrates. Include snacks between meals.
Increase carbohydrate intake around training. Many women under eat carbohydrates due to outdated messages about weight or “clean eating”. But low carbohydrate availability disrupts hormonal function⁷.
Improve sleep, manage stress and allow recovery days. Support micronutrient status with key nutrients like iron, calcium, vitamin D and omega 3 fats.
Cycle restoration takes time. But with consistent changes, most women regain regularity and feel stronger, healthier and more energised.
What to Expect During Recovery
What to Expect During Recovery
Cycle recovery may take weeks or months. Ovulation often returns before bleeding. You may notice temporary shifts in mood or appetite as hormones settle.
A single bleed does not confirm recovery. You need several ovulatory cycles for the reproductive system to stabilise. Research shows that three consecutive ovulatory cycles indicate that hormonal balance has returned¹².
Training intensity may need to adjust short term. Most women see better recovery, more energy and improved performance once cycles normalise⁵.
Final Thoughts
Irregular menstrual cycles are a sign that your body is struggling. They are not a normal part of training. Paying attention to your cycle protects your health, performance and long term wellbeing.
If you are experiencing irregular menstrual cycles or want personalised support, I can help. Book a free 15 Minute Discovery Call and we can discuss the correct plan for you.
References:
- ACOG Committee Opinion. Menstruation in Girls and Adolescents. Obstet Gynecol. 2015.
- Gordon CM et al. Functional Hypothalamic Amenorrhoea. Endocr Rev. 2017.
- Barrack MT et al. Bone health and menstrual status in athletes. Med Sci Sports Exerc. 2010.
- Loucks AB. Low Energy Availability and the Hypothalamic–Pituitary–Ovarian Axis. J Clin Endocrinol Metab. 2003.
- Mountjoy M et al. IOC Consensus Statement on RED-S. Br J Sports Med. 2018.
- Berga SL et al. Stress and HPA axis suppression of reproductive hormones. J Clin Endocrinol Metab. 2003.
- Williams NI et al. Macronutrient intake, leptin and reproductive function. Hum Reprod. 2015.
- Misra M et al. Weight loss and reproductive axis function. J Clin Endocrinol Metab. 2004.
- Teede H et al. Diagnosis and management of PCOS. Lancet. 2019.
- Reed BG, Carr BR. The normal menstrual cycle and the control of ovulation. Endocrinol Metab Clin. 2018.
- Gordon CM et al. Functional Hypothalamic Amenorrhoea. Endocr Rev. 2017.
- De Souza MJ et al. The 2014 Female Athlete Triad Coalition Consensus Statement. Br J Sports Med. 2014.
