Over the last half century improvements in training technique, clothing and equipment have helped athletes become better, faster and stronger.
But it's only since the 1990s that scientists started to work out that the training and nutrition needs of men and women were different.
Before that, most of the research was done on men and so training programs for women were just scaled down versions.
Dr Stacey Sims has been pioneering a different approach, working on the premise that women are not just small men. She's an exercise physiologist, nutrition scientist, former triathlete and author and has spent the last two decades researching female physiology so as to optimise women’s training, nutrition, recovery and hydration needs.
She remembers her own early training experiences as revolving around her menstrual cycle.
“A lot of it was based on that whole, three weeks on, one week off, which is very much periodised.
“And if I look at it from a female perspective I was leaving a lot of performance potential on the table, by not paying attention to my own natural cycle.”
There are times during the menstrual cycle when women can hit, high intensities” she says.
“You can push it hard and get really good training adaptations and then there are other times where physiologically your body isn't going to allow you to hit those intensities. So, it's better to do more maintenance stuff.”
At the time the impact of exercise on a woman’s body and menstrual cycle was little understood or discussed, she says.
“It used to be a badge of honour not have your period because people would say ‘Oh I’m training so hard, I've lost my period, this is great. And no one would talk about it, and coaches didn't want to know, if you said, ‘Well you know I'm not feeling very well because it's that time of the month, they're like la, la, la, la, they don't want to know.
“But we know now that if you don't get your period, that's a sign of dysfunction. That's the first thing to go when you start getting overstressed, over-trained, not adapting well and you're not eating enough.”
Past research done on recovering athletes has been male-centric and this has led to women working against their own physiology, she says. Now we know better.
“We know from the new genetic research that is coming out there are inherent sex differences in muscle enzyme activity between men and women. So, women can't do three days of high intensity activity in a row.
“Men can, they can do three or four. But it's just that time lag and the difference in muscle enzyme activity that inhibits women from doing that third day of high intensity without really getting into a breakdown state.”
However, that research isn't necessarily being built into training programmes for women.
“I still get backlash now from coaches who are like 'but you know, this is how we train' and I’m like, 'well, you're looking through the male lens you've always done this, this is how you've been taught'.
“But if we take away that sex-focus lens and step outside of it, and work with the individual, you're going to get so much more out of your athlete without putting them in this compromised state of over-trained, overtired and under-recovered.”
The rise and fall of hormones during a woman’s menstrual cycle have a profound impact on performance, Dr Sims says. The first two weeks are a low hormone phase the last two, the luteal phase, is a period of high hormone production.
“It's when you start getting that rise of oestrogen progesterone is when we start seeing all the systemic changes, because they're not just reproductive hormones, progesterone is thermogenic it drives the core temperature up by about 0.5 degrees Celcius, it also makes us kick out more total body sodium.
"So, we are more predisposed to what we call hyponatremia, meaning water intoxication, if we're just drinking plain water.”
Different women feel different at various stages of their cycles, she says.
“We know that with low oestrogen progesterone you can hit those high intensities and you can build lean mass, and you can drop body fat, if you're training in that low hormone phase.
“And around ovulation, some women feel really bulletproof and some women feel really flat. If you’re woman who feels bulletproof, it's because you have a bigger surge of oestrogen and oestrogen is anabolic. So, you can really hit that training day hard.
“After ovulation, there's a couple of days where you can do some more steady state work, where it’s really not that super high intensity and we’re able to get more maintenance.”
As the hormones rise women need more protein, she says.
“Women need more protein primarily because we need more circulating amino acids and leucine. Leucine is a critical amino acid for preventing brain fog but also for developing muscle protein synthesis and lean mass.
“If we have low levels of leucine in the brain because of elevated oestrogen, then we're also not being able to trigger muscle protein synthesis as well as we should be able to. “
It is also important to be aware of sodium loss, she says.
“When we talk about fluid balance and losing excess sodium, I kind of chuckle now when I see all the advertisements about taking a diuretic to prevent the bloating …. in fact, we shouldn't be doing that, we should be salting our food because we're kicking out so much extra sodium.”
The feeling of being bloated is not from water retention, she says, but from water redistribution.
“Whereas if you salt your food, and increase your total body intake and storage of sodium, you have that food redistribution so you don't feel bloated.”
Just drinking plain water in high hormone phase days while training is not the answer.
“They're very close to clinical hyponatremia, which is low blood sodium, that can cause seizures, that can cause clinical issues where you end up in the hospital and in certain times, we find that people actually died from it.”
This is compounded by the fact women can have muted thirst responses.
When we are in a low hormone state, our plasma osmolality, or the measure of the stuff that's in our blood, sits around 285 to 290 [mOsm/L] in the high hormone phase and that drops to about 275 to 280.
Clinical hyponatremia is at 270 mOsm/L, she says
“This is where we can get into the whole conversation of drink to thirst or drink X amount. And it's not really an argument so much until you get into that high hormone phase and then it is sip, sip, sip on functional hydration. So, that's something that has a little bit of salt in it and a little bit of carbohydrate in it, but not a sports drink, because that is not a way to hydrate.”
Hormones also have an impact on carbohydrate uptake, she says.
“It's the way oestrogen affects our metabolism. When we have low oestrogen we can access the carbohydrates pretty readily, but when oestrogen starts to rise it facilitates free fatty acid release, so we end up using more fatty acids during exercise in that high hormone phase so that we can't access the carbohydrate very well.”
Women doing high intensity training during an elevated phase should take exogenous carbohydrates, she says.
Fat burning during exercise is also complex, Dr Simms says.
“We tend to burn more fat [than men], but we also tend to store more.
“If you're burning more fat during exercise then the signal is to store more afterwards, especially in the muscle. But the way we can capture that is say, Okay well we'll burn more fat but afterwards, let's hit that protein to bring down that that response for storing fat.”
Women need more protein than men, and older women more than younger women, she says.
She recommends for older women 30 to 40 grams of protein after exercise, a fast-acting protein such as a whey protein isolate is ideal, or one based on egg whites.
Another good recovery food is low-fat Greek yoghurt, she says.
As women enter menopause, their training should change too, she says.
It's no longer the long, slow recovery type exercise sessions, you're looking at that high intensity, multi-directional type of work so that you are stimulating lean mass development, you're stimulating the loss of body fat.
“But more importantly, you're stimulating bone growth and you are stimulating neuromuscular fibre development and the actual firing of the muscle because that's what we lose at the onset of menopause, we lose bone mass, we also lose that anabolic stimulus for developing lean mass.”
Circuit training, boot camps and cross fit are ideal forms of exercise as women get older, she says.
All of that is very beneficial if you're wanting to see and or make changes in body composition and bone density.”
The talk test is a good guide as to how intense training should be, she says. Rather than heart rate.
“If you're out for a very low intensity kind of aerobic activity and you can't hold a conversation, then you're going too hard and the flip side of that is if you're trying to hit those high intensities and you can still talk then you're not going hard enough.”