How triathletes can harness their hormones for optimal performance

Hormones are vital to a triathlete's health and performance, at all ages. But how can we optimise them to ensure we reach our athletic potential? Dr Nicky Keay explains…

Lars Lomholt of Denmark reacts after winning Ironman Portugal Cascais on October 15, 2022

Hippocrates, often described as the father of medicine, would have made a very good triathlon coach. He advocated that the “surest way to health” was by giving each individual just the right amount of nutrition and exercise; “not too little and not too much”.


Optimal health is a prerequisite to athletic performance. In other words, personalised training load, fuelling and recovery will mean triathletes can strive to be citius, altius, fortius (faster, higher, stronger)!

The foundation for athletic performance

Although Hippocrates recognised the practical strategies to attain optimal health and therefore performance, he did not know why. We now understand that hormones are the missing link.

Hormones are chemical messengers transmitted in the blood stream. Just one hormone found in both men and women, such as oestradiol (most potent form of oestrogen) or testosterone, has access to all the cells in the body.

On arriving at a cell, the hormone homes in on the DNA in the nucleus to direct gene expression and the production of proteins: the right ones, at the right time and in the right amount for optimal health.

In other words, hormones bring our DNA to life. Hormones work in collaborative teams to support physical and mental health[1].

How athlete behaviours harness hormone action

Hormone action is influenced by our behaviours of exercise, nutrition and sleep. Furthermore, hormones drive the positive adaptations to exercise training.

In order to harness our hormones to gain maximum benefit from triathlon training, it’s important to aim for the optimal balance of training load, nutrition and recovery. Not too little and not too much. Timing is also crucial.

Hormone release runs on internal biological clocks. These hormone clocks can have short daily time scales like cortisol; monthly timing like the hormones of the menstrual cycle; and the longest timescale of all – the lifespan.

The challenge is to synchronise the timing of external athlete behaviours with internal hormone clocks. The optimal combination and timing of these athlete behaviours will depend on the individual characteristics of the athlete, including their starting fitness level, biological sex and age[2].

The hormone ages of a triathlete

The child triathlete

The endocrine system (all the hormone secreting glands and the hormone orchestra) have not fully developed in a child. This is one of the reasons why a child should not be encouraged to train like an adult as the hormone networks can’t deal with high-intensity training.

Not only will this type of training not bring positive adaptations, but also risks early physical and mental burnout. Rather, focusing on enjoyment and technical skills will support nurturing the aspiring young triathlete.

The teenage triathlete

The teenage years see an explosion in hormones! In particular, the sex steroid hormone axes come to life. For young women this means the start of menstrual cycles with oestradiol and progesterone as the protagonist sex steroids.

In young men, puberty sees the increase in testosterone towards adult levels. As hormone networks mature at different times and rates, training load with appropriate nutrition and recovery will need to be personalised according to the stage of hormone ‘maturity’ of the teenage triathlete.

The adult triathlete

Hormone networks should now be working at full potential to support positive adaptations to triathlon training. For female triathletes, understanding and tuning into the fluctuations of hormones that occur during the menstrual cycle can help[3].

This is also the time when there will be many demands outside of triathlon training, such as work and social life. This can lead to imbalances in behaviours which have negative impacts on hormone health.

For example, relative energy deficiency in sport (RED-S) is where there’s a mismatch in energy demand from training and energy intake[4]. This can lead to low energy availability, requiring the body to go into ‘energy saving’ eco mode.

This includes downregulation, or a powering off of the hormone networks. The reproductive hormone axis is one of the first to be switched off to save energy. In women this can result in menstrual disruption, including lack of periods (amenorrhoea).

In men, low energy availability will cause reduced levels of testosterone associated with reduced libido and fatigue.

Low levels of hormones put triathletes at risk of underperformance and injury. Fortunately, low energy availability and RED-S is a reversible situation through rebalancing of athlete behaviours around training load, nutrition and recovery to reboot hormone networks.

The masters triathlete

Hormones start to wind down with advancing age, but modifying athlete behaviours in step with hormone changes can secure continued triathlon performance.

For example, the decline in growth hormone and testosterone in both men and women means that increasing strength training will help support these ‘anabolic’ (tissue building) hormones and maintain good body composition and metabolic health.

For female triathletes, the menopause sees the retirement of the ovarian function and a consequent dramatic reduction in oestradiol and progesterone. Although this change in hormone levels is a natural physiological event, this can present challenges in terms of wellbeing and exercise performance.

I’m actually guiding an increasing number of female masters athletes through this transition, to support women’s continued participation in sport.

Hormone replacement therapy (HRT) is a game changer for many. HRT consists of a combination of oestradiol and progesterone to maintain quality of life, with the added benefit for long term cardiovascular and bone health.

It’s important to mention that testosterone replacement is not permissible for either male or female triathletes under WADA regulations. Fortunately, modification of triathlete behaviours is a legal way to support hormone health throughout a triathlete’s career.


Hormones are vital to a triathlete’s health and performance, for all levels and ages of athlete. Triathletes can harness the power of their hormones by ensuring personal, optimal balance of athlete behaviours around training, nutrition and recovery.

Dr Nicky Keay is the author of ‘Hormones, Health and Human Potential’. Dr Keay offers hormone health advisory appointments for athletes seeking to attain their personal full potential.


[1] Keay N. Hormones, Health and Human Potential. 
[2] Keay N. Sports Endocrinology – what does it have to do with performance? British Journal Sports Medicine 2017
[3] Keay N. What’s so good about menstrual cycles? British Journal Sports Medicine 2019
[4] British Association of Sport and Exercise Medicine  


Top image credit: Nigel Roddis/Getty Images for Ironman