Ten Critical Sex Differences In Exercise and Recovery

In 2014, a review looking at almost 1400 peer-reviewed studies from sports science and sports medicine journals, found that on average, women made up just 39% of study subjects.


This finding was published in The European Journal of Sports Science.

Bethany Brookshire built on this review in 2016. She added up the number of studies that included women in two major academic journals: ‘Medicine and Science in Sports and Exercise‘ and the ‘American Journal of Sports Medicine‘.

She found that just 4% of the research was female-specific.

In a 2017 editorial published in the British Medical Journal, the authors wrote that mainly, women have been excluded from research because they’re seen as “more physiologically variable.”



female athlete research


Should we be surprised then, that so much of what we read and hear about fitness actually don’t apply to women?


Here are ten factors with different implications on training, performance and recovery depending on gender that I bet very few people are aware of:


1. Intermittent Fasting (IF)

Intermittent Fasting is bad for active women

The original research on IF was conducted primarily on males who were diabetic and obese.


Men respond differently to the stress of no or low calories than women.

This is due to the neuropeptide (kisspeptin) response, and sensitivity of a woman’s endocrine system to a non-fed state.

Unfortunately, this is not generally known.

Women all over the world starve themselves for extended periods, thinking this is finally the answer to help them manage their weight.


Let’s look at the research on men vs women: 



The (beneficial) effects IF can have on men:

– a strong parasympathetic response (clarity of mind / cognitive focus)

– improvement in blood glucose control

– massive autophagy (the body’s way of cleaning out damaged cells, in order to regenerate newer, healthier cells)


The effects IF have on women:

– a sympathetic (stress) response to not having enough calories, which cause anxiety, depressed feelings, brain fog and an elevated heart rate

– no improvement in blood glucose control in women

– autophagy is minimal

– can be a precursor to menstrual dysfunction seen in low energy states due to the sensitivity of kisspeptin

– it signals an increase in visceral fat (the fat around the essential organs, the protective fat that’s really hard to mobilize and increases cardiovascular risk.)

– long term effects of intermittent fasting with exercise is endocrine dysfunction, increases in abdominal fat, more depression and subsequent fat gain

If you’re a woman, adding intermittent fasting on top of exercise adds to the stress of denying our bodies important nutrient signaling. The result is that your body starts storing more belly fat.

A study showed that in active women, the longer they stay in a catabolic state, the more they disrupt your endocrine system and resting metabolic rate (RMR) – EVEN IF YOU EAT ENOUGH CALORIES IN GENERAL!

This means that even if you eat a sufficient amount of food in a day – periods of fasting, or delaying food intake, will impede your metabolism. 



2. Ice Baths


Ice baths don't work the same for women and men
Cold immersion tricks your body into redistributing the blood from the skin back into circulation through the muscles. This makes ice baths a popular recovery protocol.
In her book ROAR, Dr. Stacy Sims points out how a post workout ice bath has a different effect for men vs women:
  • Men’s blood vessels naturally constrict after exercise, which causes blood to move away from the skin and back into central circulation.
  • In contrast, women’s vessels vasodilate post exercise, causing our blood to pool in our skin. This results in lower blood pressure and reduced blood flow to the damaged muscle.



An ice bath after a hard session will therefore be of way more benefit to women as it would be to men.



For us girls, an ice bath after an intense workout session can help recovery by:


  • accelerating vasoconstriction to get blood back centrally
  • assisting in increased blood pressure for removal of metabolites, and
  • circulation of oxygen into the muscles.




3. Running (And Other Cardiovascular Sports)

cardiovascular men vs women


As you are about to find out, a woman is actually at a significant disadvantage (compared to men) when it comes to cardiovascular sport.


As taken from ROAR by Dr. Stacy Sims:
  • Women have a smaller heart, smaller heart volume, smaller lungs (25 – 30% less capacity than men) and lower diastolic blood pressure, which predisposes us to have lower max heart rates and greater problems with dehydration in the heat.
  • This also means we pump out less oxygenated blood with every beat – about 30% less cardiac output than men.
  • Less oxygenated blood means we have to breathe more often, and as a consequence, our respiratory muscles need to work harder and use a lot of energy.
  • When we push the pace and breathe hard, it can be difficult to race against guys because less bloodflow is going to our legs.
  • Testosterone increases the production of red blood cells, which absorb and carry oxygen to working muscles.
  • All of this means we have a lower VO2max than men – about 15 – 25% lower on average, as shown in the chart above.

Gerda Steyn

After reading the above for the first time, I realised just how impressive Gerda Steyn’s (pic above) Comrades 17th overall place was in 2019. (She also broke the ‘up’ record for women that same year by more than 10 minutes, clocking a time of 5:58:53.)




4. Heat Training

women and heat training

Firstly, consider that the ‘body’ referred to when saying ‘the human body is 60% water’, is that of a man’s.

For women, that number is closer to 50%, because we naturally have a higher fat percentage.

Fat does not carry as much fluid as muscle, which men have in higher percentages.

Both men and women have increased core body temperatures when they get dehydrated during exercise.

Women sweating less than men (about three times in the study linked to here!) however, results in our core temperature rising twice as quickly as men’s when exercising.

The study highlights that at the same extent of dehydration (during exercise), women are at higher risk of experiencing an increased heart rate and core body temperature.

Dr. Sims writes in her post on heat that men have higher overall sweating capacity. This is an advantage in hot and dry conditions, where sweat evaporates and helps cool you down.

In hot and humid conditions however, sweat evaporates less and then this cooling mechanism does not work so well.

Women have and use more sweat glands, but generally sweat less and should bear hot and humid conditions better.

I have to say here that I personally suffered running in the hot and humid weather of Thailand. I sweated bucket loads and believe that some women (like myself) may possibly sweat more like men do. 


Another difference is in heat acclimatisation strategies.


Research shows that women need to do about twice as many heat adaptation sessions to get the same degree of adaptations as men.







5. Altitude

Women use more fat at altitude

At altitude, men’s bodies chomp on carbohydrates, while women’s bodies prefer to use fat for fuel.

This sex difference can put women at an advantage, if it’s a long race.



Therefore ladies – if you want to beat your male friends, challenge them to a high mountain ultra.


Bear in mind though that women are more susceptible to altitude sickness in the high hormone phase. So, time it well.








6. Periodisation  / Programming


Periodisation for women
A typical mesocycle (training block in a larger macrocycle) consists of a 3 weeks on, 1 week off schedule (see image above).


This may work in any instance, for men. Their hormones don’t fluctuate on a monthly or weekly basis.

For women, on the other hand, following this schedule blindly will not yield the best training quality and adaptation.
Pre menopausal women should firstly track their cycles to establish its duration.
Recovery times should fall in the high hormone phase.
See the last point (ten) for more on this.




Periodisation (intentional pun, ha) for female athletes should therefore absolutely be synced with a woman’s menstrual cycle.


Coaches should be aware of and understand this!








7. Post Workout Recovery Window

Women have a shorter post workout recovery window
The post workout recovery window for women and men is not the same – a critical sex difference with vital implications.
Unfortunately, few athletes, coaches and trainers are aware of this.

Women need protein post workout more than men do, and we need it fast.



This is because progesterone boosts muscle breakdown in women – it makes us more catabolic.

Post workout protein will support and strengthen and muscles in recovery.

Whey protein is the most practical option, and preferred for its quick uptake and favourable leucine content.

Leucine – one of the three Branched Chai Amino Acids (BCAAs) – is the most potent activator of protein synthesis.

You need 30g of protein (40g if you’re in menopause) within 30min of finishing your workout (men have up to 3h).



8. Women Use Fat For Fuel

fat adapted


Women oxidize more fat and less carbohydrate than men at the same relative intensities of exercise.


One study specifically, found that at an intensity of approximately 65% maximal oxygen consumption (VO2max) – a moderate intensity – , women have higher rates of lipid (fat) oxidation and lower rates of carbohydrate and protein metabolism compared to men.




This phenomenon essentially makes women ‘fat adapted‘ by nature.


Becoming ‘fat adapted‘ has become popular for especially endurance athletes or those wanting to lose excess weight.


It is believed that following a Ketogenic (low/no carb) diet will bring you to this state, in which your body burns fat for fuel instead of carbohydrates.


Clearly, this is already the case for women.


This preference of the female body to burn fat as fuel, become even more pronounced in the high hormone phase (see last point) and at altitude 











9. Calorie Deficit Diets Don’t Work So Well For Women, And Can Cause Permanent Thyroid Damage



Women Lose Less Fat Than Men
From the onset of puberty to menopause, women maintain a greater percentage body fat than men despite smaller energy intake per kg of muscle.


While women take in less calories per kilogram of muscle mass, AND have a preference for burning fat during exercise (point eight), women still lose less fat than men when faced with a similar energy deficit. 

One explanation for this is that women store fat more efficiently – which is probably true. Our bodies are primed for reproduction, unlike men’s.

I would argue however that the general higher muscle mass in men – which results in a higher resting metabolic rate (RMR) – is a top dog when it comes to fat loss

This is why two key elements in my approach to fat loss / improving body composition are:



 – For females: after being in a calorie deficit (Low Energy Availability – LEA) for only four days, T3 (the active form of your thyroid hormone)  starts to drop





10. Low Hormone Phase and High Hormone Phase


High Hormone phase and Low Hormone Phase
Unlike men, women of reproductive age have a menstrual cycle that bring about hormonal fluctuations on roughly a monthly basis.

These fluctuations can be classed into a 1) low hormone (follicular) phase, 2) ovulation, and a 3) high hormone (luteal) phase.

A 28 day cycle is pretty much text book (see image above), but some women have shorter cycles, closer to 23 days, and others up to 35 days.

When and how long each phase (follicular or luteal) is depends on cycle length, and can therefore be different from the image above.




Each phase has important implications for exercise and recovery.



During the follicular phase, women are hormonally most like men and in terms of exercising – feel best and is the best time for physical adaptations to exercise.

As shown in the image above, the follicular phase falls in the first two to three weeks of a 28 day cycle. Consequently, this is the phase you want to throw balls to the wall (purposeful pun) in your sessions.

Women who are estrogen sensitive, may feel flat during ovulation. The best time to hit a PB though, is the 48h directly after ovulation. 

During the luteal phase – the last about 5 days of a 28 day cycle – progesterone and estrogen are high. These elevated hormones can make it hard to hit high intensities (due to an even lesser reliance on glucose) and recover well.

This makes this phase an appropriate time to tone things down and recover.

Not tracking cycles and understanding each phase’s implications, can lead to frustration and confusion for both athletes and coaches.

In addition, not utilising each phase optimally can leave a lot of performance potential on the table.






It’s time coaches and female athletes get informed of the gender differences that exist in diet, exercise and recovery.

Not only for optimal performance and results, but also for the enjoyment we seek when participating in sport.


Sadly, the majority of the so called experts are failing women big time by not paying attention to new fitness research and information. 



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