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Why women are NOT small men.

Updated: Feb 17, 2022

written by, Louisa Maslaveckas

Why Women are not small Men: A deeper look into the female physiology

After years of experiencing fluctuations in my training performance, I couldn’t understand how I could feel so different doing the same exercises just days apart. I would put it down to fuelling incorrectly or sore muscles, which are both quite likely. However, it was only when I stumbled upon a podcast where several health professionals were discussing the importance of training around your menstrual cycle that it all really clicked. It has been a hot topic in the last few years. Thanks are due to the inspiring lady that is, Dr Stacy Sims, who dedicated her PhD to understanding female physiology. Dr Sims ignited the paradigm shift with her eminent statement ‘Women are not small Men’. I wanted to share her findings with you and by doing so, debunk some of the pseudoscience around women in sport.

You may have wondered how men can reach performance and aesthetic goals much quicker when following the same training plan. When women and men are both training at the same capacity and intensity, women tend to feel much more fatigued and don’t reap as much benefit as men do.

The greatest physiological difference between men and women is visually obvious, men are bigger. What you can’t see though, is that women have a smaller heart, with reduced heart volume and lungs possessing 30% less capacity compared to men. Having a lower diastolic pressure means that we have a lower maximum heart rate, reducing the amount of oxygenated blood we are able to pump around the body. This results in women needing to work twice as hard to generate the same level of energy that her male counterpart can. For example, say you’re competing in a 200m sprint - pumping enough blood to your legs becomes secondary to the primary oxygen cost producing blood flow to your respiratory muscles at maximal effort. You also have to factor in the presence of testosterone in men, which during maximal effort can boost their advantage. Testosterone increases the production and concentration of red blood cells by 6%. The role of red blood cells is to carry oxygen readily around the body. So suddenly this 200m sprint doesn’t look too fair, does it.

The muscular composition of men and women is generally the same, with the same percentage of type 1 endurance (aerobic) fibres and type 2 power (anaerobic) fibres in both sexes. The interesting difference is that the largest fibres in women are predominantly type 1 endurance fibres. Thus, men may have the upper hand when it comes to strength training. Research suggests that women are around 52% as strong as men in their upper body and 66% in their lower body. However, this strength gap may be lower in well trained women. Female bodies are better designed for endurance exercise, which is why women generally make better runners than men. However, data shows that when women and men train equally, their relative strength and hypertrophy gains are not too different.

Men have larger type 2 fibres which means they have a higher glycolytic capacity. Essentially this enables them to burn through glucose in the absence of oxygen. Women, on the other hand, spare glycogen by using fat reserves or in periods of extreme glycogen deficit burn through muscle. Favouring fat to fuel exercise sounds like a good thing? Not exactly.

Within the menstrual cycle there are two hormone phases, high and low. Hormones are the body’s chemical messengers between your brain and organs. They control everything we do: mood, sleep, metabolism and growth and repair of muscles. When we are in the low hormone phase (1-14 days of the menstrual cycle) our physiology is the most similar to men, which seems quite ironic during our period. In this phase, we metabolise carbohydrates and recover similarly to men. The two hormones I am referring to here are estrogen and progesterone. These hormones fluctuate in concentration throughout the cycle. Estrogen consistently maximises fatty acid oxidation capacity throughout the cycle (choosing to use fat as fuel). So, with this in mind, if a female is training their anaerobic system (HIIT or weight training), this type of explosive and high intensity exercise really requires glucose as its preferred energy source. When we are in our high hormone phase of the menstrual cycle, estrogen is high. High levels of estrogen inhibit the availability of glucose. Therefore, if carbohydrate availability is low pre-exercise, you are going to struggle to perform optimally and push past your threshold. In this high hormone phase, estrogen also acts like an anabolic inhibitor making it harder for women to recover and grow muscle. This is counter to a lot of current propoganda promoting that we train ‘fasted’ because ‘it makes you burn more fat or is more metabolically efficient’.

What does fasted mean? Fasted implies limited food or calorie intake, generally a low energy availability. In fact, research shows that women actually train best in a fed state to maximise adaptations. Considering we already oxidise fat efficiently, by training fasted you are actually doing your body a disservice.

Typically, this style of fasted training is done first thing in the morning, pushing the first meal to the middle of the day. The general inference is that women should train more and eating less. Exercise is a stress in itself and you need to fuel and encounter the stress to overcome it. Women who exercise fasted create big gaps of no food which means their bodies have been in a significant breakdown phase making it harder to recover and hindering any real benefits of their workout. If you are considering fasting as a style of diet you should first pay attention to your hormones and current training programme to make sure you are not in a consistent low-calorie deficit. Maintaining an extremely low energy availability can lead to RED-S.

RED- S syndrome (relative energy deficiency in sport) was a consensus statement published in 2014 by the International Olympic Committee (IOC) to address the damage on physiological functions through low energy availability across men and women. Low energy availability (LEA) is defined by energy intake being less than optimal for energy output or in other words, not eating enough to provide your body with adequate nutrients to recover from your everyday demands including exercise stress. In fact, 45% of recreational female exercise is carried out in a subclinical low energy state. The problem with LEA, especially for women, is due to its direct link to menstrual irregularities and thyroid function. It can lead to an increase in belly fat and feeling fatigued. The physiological implications that come with LEA also include a reduced metabolic rate, sub optimal protein synthesis and reducing bone health and density. In women, irregular or absence of a period is the number one indicator for symptoms of RED-S. Some women have been trying to prevent their period as a means of getting ahead in training or competition for years. But what if I told you that having a period and functioning menstrual cycle is actually an ergogenic aid for performance?

The problem with the oral contraceptive for performance

Taking the pill as oral contraception (OC) to mitigate your period for training purposes can be really detrimental to performance and health. The pill contains synthetic versions of the hormones progesterone and estrogen and these do not function like your natural hormones do. Research states that OC can actually downregulate our ability to hit the top of your V02 max/ high end intensity. These extra hormones create fluctuations in concentration messing with your natural cycle, causing higher levels and creating a plateau effect on performance and adaptation. They also increase your risk of developing blood clots and deep vein thrombosis (DVT) which can be extremely dangerous when travelling long distances and sitting for a significant period of time on an airplane. Evidently there are multiple reasons why people choose oral contraception. However, it is important to be mindful of other options available and understand the full potential of adopting a more natural approach to cycling and mapping your period. For a little more information on optimising your training and nutrition around your cycle, follow this link to my previous blog.

But doesn’t preventing your period benefit your training?

A synthetic progesterone tablet known as norethisterone is commonly given to female athletes to delay their period. Sound good? Perhaps, but many female athletes actually experience a negative impact and decline in their performance when using norethisterone. What does norethisterone do? It increases progesterone intake in your ovaries and adrenal glands. Your body essentially begins preparing for conception and pregnancy. Paula Radcliffe spoke out publicly about her own experience with norethisterone, aiming to educate and promote the benefits of having a regular menstrual cycle as a performance aid. In fact, Radcliffe actually broke the world record in the 2002 Chicago Marathon, while experiencing severe menstrual cramps. It was during the 2013 World Championships that sparked Radcliffe's reaction. Jessica Judd was set to place top in the 800m race but lost. Judd was given norethisterone by her coaches just before the race to delay her period. Surprising information? Absolutely - but this still goes on with misinformed coaches and trainers who believe that ‘no period’ is problem solving.

If you struggle with symptoms of PMS such as feeling tired, bloated and experiencing brain fog, you need to understand that it has an inflammation related effect. Estrogen affects the kidneys and progesterone causing a fluid shift which leads to bloating. Estrogen causes the blood brain barrier to hypersensitise serotonin so we get that brain fog. Serotonin is the hormone that controls and stabilises our mood. It is the hormone that enables the nervous system cells and brain cells to communicate. We can manipulate our nutrition to mitigate some of these symptoms by supplementing with magnesium and zinc. Magnesium and zinc are in high demand when building the uterine lining 5-7 days before your period starts. We also need magnesium and zinc to help with the function of our immune system and muscles, therefore we need an extra boost during this phase. This helps the immune system, reduces muscle fatigue and cramping and the intensity of uterine contractions. Aim for 45mg of zinc and 250mg magnesium a day.


Recovering is as important as your training, neglecting it impedes any type of performance goal. It is also harder for women to recover due to the sheer fact of our limited ability to access stored glycogen, especially when estrogen is high. It is essential that you consume carbohydrates post exercise and more so if you trained in a low carbohydrate state (fasted). Insufficient glycogen in the body results in protein breakdown, impairing recovery. Placing you in a protein deficit which hinders muscular repair and growth. Men on the other hand have an extreme advantage with recovery. During exercise they have a large capacity to fuel with glycogen stores and then recover utilising fat reserves post exercise. Their metabolism remains elevated for up to 21 hours unlike women who have a short 3-hour window post exercise. This explains why men tend to drop weight much quicker than women when you follow a similar training programme. So, in summary, to achieve goals, fuel performance with carbohydrates and recover with a high protein and high carbohydrate meal post exercise to avoid any muscle breakdown or unnecessary body fat being stored.

In the high hormone phase, prioritise working on technique and functional movement, thereby lowering cardiovascular stress. By reducing overall stress, you reduce cortisol. If you focus on technique in this phase, your form is going to get better which will set you up nicely for overreaching in the lower hormone phase. This allows you to have a better exercise stress stimulus which means you can recover optimally rather than over-stressing the body.

Thanks for reading, I hope you found this useful.

Until next time,

Lou X


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