Iron deficiency is a challenge for many female athletes, like Super Netball's Zara Walters

Zara Walters has spent a lot of her time as a professional athlete feeling heavy, tired and lethargic.

The Melbourne Vixens player knew something was wrong when she struggled to get through training sessions.

"I felt quite fatigued, I felt heavy in the legs, and it just didn't feel right," Walters told ABC Sport.

Even trying to wind down was hard.

"You're trying to nap every 10 minutes," she said.

"It is very hard to recover as well."

It was not until the 22-year-old had some blood tests at the Victorian Institute of Sport (VIS) that she found out she was iron deficient.

"I think it was more of a relief that I knew it wasn't that I was unfit and I couldn't get through sessions," she said.

"It was [also] a relief to know that there is a management to it."

Maintaining normal iron levels is an ongoing challenge for many athletes.

Walters has regular blood tests, works with a nutritionist to make sure she is fuelling properly, introduces supplements when they are needed, and has the occasional iron infusion.

After experiencing symptoms since her teens, the first infusion was a game-changer.

"I think it was the best I've felt. It was life-changing," Walters said.

Why are athletes at risk more than others?

Iron fuels energy production, is needed for a strong immune system and enables sharp brain function.

If the balance is disrupted, things like fatigue and poor performance creep in.

Iron deficiency affects athletes more because increased exercise can deplete the body's stores.

One recent study showed that up to 35 per cent of female athletes are low in iron, compared to 5 per cent of the general population.

VIS medical director Dr Susan White says that was due to a variety of factors.

"There is a substance called hepcidin which exercise increases. And if you increase your hepcidin, iron absorption goes down," Dr White said.

"We also know it's common in females because of menstrual blood loss, whether it be female athletes or females in general."

Targeted testing and surprising results

Three years ago, VIS started proactively monitoring its athletes' iron levels with extreme attention to detail.

They did targeted blood testing of females, long-distance runners and athletes in weight-controlled sports.

The results were surprising.

"Our expectation was that we would find 25 to 30 per cent of our female athletes being iron deficient, which is the statistics that we see in the literature," Dr White said.

"But we found more than 50 per cent of our athletes were iron deficient."

With a focus on dropping those levels VIS built individual plans.

Treatment involves a food-first approach, with dieticians guiding athletes towards iron-rich foods like red meat, leafy greens and lentils. Then iron supplements, and an infusion for severe or persistent cases.

Just as surprising as the number of athletes affected was the length of time it took for them to reach optimal iron levels.

"We thought we would have them all fixed in 12 months," Dr White said.

"For most of our athletes, it's really taken 12-18 months to get their iron levels up to where we want them."

Ongoing monitoring is needed, especially since symptoms can be so easily dismissed.

"It is hard to pick up on those symptoms because you don't just wake up one day and feel lethargic," Walters said.

"I think it's a slow build, but I can feel when I am getting a little bit low.

"I'm trying to get through sessions and I'm feeling heavy. I feel weak in the gym. And that's probably the time where I do request a blood test again."

So how do you increase iron levels and keep them up?

VIS's approach from reactive to proactive care seems to be working.

They now test athletes for iron levels during their annual intake.

For those at higher risk, like Walters, they are tested every three to six months.

Over the past three years, VIS has averaged about 30 iron infusions a year. Only three of those infusions were for males, and those were in long-distance sports.

"The trend is slowly decreasing, which we hope possibly is an indication of our ability to perhaps pick these up earlier and progress through increasing iron before we get to an infusion," Dr White said.

"But the reality is there's always going to be a group that we just can't increase with tablets and diet alone."

Infusions also come with risks, like anaphylactic reactions and skin staining. They can also have anti-doping implications.

But when they are used athletes and coaches have reported good results.

"It takes probably a week to start to notice the difference," Dr White said.

"We get feedback from the coaches and they notice a difference. They seem to be training better; they're a bit more alert.

"One of the things they also report is that they stop needing afternoon naps."

No quick fix

VIS has been collecting its data for the past three years and is collaborating with La Trobe University to publish its findings.

Dr White's key insights so far include that iron deficiency is more prevalent and harder to correct than expected.

And with 450 athletes on the books, it also requires persistent follow-up and teamwork from doctors, nurses and nutritionists.

"We have got a great spreadsheet to work out who needs follow-up, who needs to check in with the dietitian," Dr White said.

Walters says it has been a game-changer for her.

"The management of mine has been incredible and I've been able to live a lot better quality of life, and to train so much better as well," Walters said.

"If it is ongoing and you do feel some of those symptoms, I think it's worth getting a blood test to check."