At first, it’s like a gentle spin class, except for the medical equipment we’re hooked up to: an oxygen mask, heart-rate monitor and sphygmomanometer (that machine with the inflatable armband that measures blood pressure). They’re all recording our exertions on an exercise bike. “You don’t feel lightheaded? Any chest pain?” asks professor of clinical exercise physiology Itamar Levinger. “No,” we say, muffled by the breathing apparatus. In fact, it feels like we could keep this up all day – for now.

We’ve come to his exercise lab at Victoria University to undergo several fitness tests, including this “gold standard” measure of our VO₂ peak. Levinger dials up the resistance. Suddenly, it feels like we’re pedalling uphill, then as if we’re riding through sand. “Keep pushing! Now the test really starts,” he yells. “Now the motivation has to come!” We pedal harder, inhale lungfuls of air and channel visions of the Tour de France. “Go, go, go!”

On any given day, people are bombarded with advice about how to get “fit”: exercise for at least 150 minutes a week, walk 10,000 steps a day, perform high-intensity interval training, lift weights, sign up for Pilates, get “marathon ready” in weeks. “People just see these unattainable, unrealistic approaches to fitness and the rabbit holes of what they should be doing,” says Matt Hornsby, a former high-performance manager at several AFL clubs, “whereas in the end, if you keep it simple, and you’re consistent over weeks, months, years – that’s how you get the best return.”

So what does it mean to be fit anyway? How fit should we be? What would we do to get there?

How fit is ‘fit’?

Dive into the world of fitness, and you’ll find as many ways of defining fit as there are ways of exercising. You could be fit for a hiking holiday, fit for walking home if the train is cancelled or fit to play with the grandkids. But fit compared to whom? “I’ve run a couple of marathons in reasonably good times, but really excellent marathon runners would look at me and say, ‘you’re not fit’,” says David Scott, an associate professor of exercise physiology at Deakin University.

Fitness can be understood in parts, says Bill Hayes, author of Sweat: A History of Exercise (and the partner of the late neurologist and writer Oliver Sacks). At its most broad, he tells us from New York, “fitness, as I think of it, at least, is something one can measure physiologically via blood pressure and heart rate. And fitness is also a kind of feeling, like, do you feel good in your body?” Indeed, wrote Galen, a second-century Roman physician: “The best exercises of all are those which are able not only to exert the body but also delight the soul.”

Hayes set out to trace the history of exercise after a question struck him one day while he was working out on a StairMaster at his gym in Manhattan. “I paused, and I just looked out at the gym floor, at all these people, men and women of all different ages and races, lifting weights, doing push-ups, pull-ups, and riding stationary bikes, and I just thought, how did we get here? ”

‘People of normal weight in the bottom 20 per cent of fitness were about twice as likely to live shorter lives than people with obesity who qualified as fit.’

In 1953, British epidemiologist Jeremy Morris compared sedentary bus drivers with conductors who went up and down the double-deckers all day. The conductors suffered less than half the rate of heart attacks. “Really, that paper is kind of the founding of exercise science,” says Hayes. “It gave a real scientific basis of proof for the benefits of movement.” A follow-up study made similar findings about deskbound civil servants compared to postal carriers.

Today, we know that physical activity can reduce hypertension, strengthen bones, reduce likelihood of type 2 diabetes and improve psychological wellbeing, among other benefits. “For the vast majority of people, the fitter you are, the healthier you are,” says Levinger. “The fact that you have some form of disease doesn’t mean that you cannot be fit.” Fitness is not necessarily about our waistline either. In fact, in a recent study published in the British Journal of Sports Medicine, people of normal weight in the bottom 20 per cent of fitness were about twice as likely to live shorter lives than people with obesity who qualified as fit.

There are several components of fitness, among them cardiorespiratory endurance (how our heart, lungs and muscles perform under prolonged strain), muscle strength (how much weight you can lift or push), muscle endurance (how many times you can repeat lifting a weight), balance and flexibility (crucial to many daily activities and preventing falls at older ages). “Particularly when we become older, muscular strength and power are more important than pure endurance to perform activities of daily living,” notes Levinger.

All these fitness components are relative to our age. Take muscle mass. For most of the population (bar those who, say, start to pump iron later in life) muscle fibres grow during adolescence and peak in our mid-20s. Our strength plateaus until about 35, when a decline starts, says Scott. “It’s pretty imperceptible for probably the next 10 to 15 years; you wouldn’t really pick up on it much. But around our 60s, that’s where you see the decline accelerating pretty significantly.”

As we become older, many of the biological mechanisms that turn exercise into muscle become less effective – which makes it harder to build strength and easier to lose it. Similarly, as oestrogen vanishes during menopause, bone density falls much more sharply among women and increases the risk of conditions such as osteoporosis. (Of course, exercise helps counteract this – more on which shortly.)

‘This was where I went, Wow! He didn’t look in the same shape as the elite athletes.’

Our fitness can also be highly specific to the type of activity we do. Dr Melissa Arkinstall, head of Exercise Research Australia, once compared an AFL player, a cricket umpire, an international-level swimmer and a high-performance jockey across a range of tests as part of a segment on TV. When the four were asked to hold a plank position – a test of core strength while resting on their elbows and toes facing the ground – it was the umpire who blitzed it. “This was where I went, ‘Wow!’” she tells us. “He didn’t look in the same shape as the elite athletes lined up with me. But it’s that specificity of what they have to do; they have to stand in the field upright, which engages the abdominals, the back. He could talk [at the same time], and he was there for nearly seven or eight minutes. Everyone else was gone.”

Given all these variables, Levinger prefers to define fitness as the “ability to perform tasks of daily living with optimal performance, endurance and strength”. “Like climbing stairs, for instance: Person A will do it very easily and complete the task and then, immediately after, will be able to do whatever they need to. Person B will climb the same stairs and be so out of breath that they will climb at a much slower pace and also need a substantial time to recover.” (We realise then that Itamar had kept an eye on us as we climbed two flights of stairs to get to the lab.)

How do we test fitness?

Back in Victoria University’s Clinical Exercise Rehabilitation facilities, Levinger peers at the data on our personal VO₂ peaks. The name stands for “volume of oxygen” and tests the maximum millilitres of oxygen our bodies can use during intense exercise – our “aerobic fitness”. Many sports wristwatches estimate a VO₂ based on heart rate and the distance you’ve run, swum or cycled, but an accurate reading comes only from exercising with a metabolic cart that analyses oxygen consumption. At some point, everyone reaches their maximum. In 2021, former Norwegian cyclist and alpine skier Oskar Svendsen, then 18, set the highest VO₂ max ever recorded: 97.5. United States marathon runner Joan Benoit – who in 1984 won the first Olympic marathon for women – holds the record for the highest women’s VO₂ max, 78.6.

For people with heart disease or asthma, heart rate or breathlessness can be the main reason they can’t continue with the test. (Our blood pressure and heart rate are tracked.) But with generally healthy people, it’s the legs that give in, Levinger tells us.

As the cycling becomes more intense, our bodies require more energy than we can deliver with oxygen, and switch to generating energy through glucose. We also produce lactate but this produces more acidity in muscle, causing a burning sensation that will, ultimately, cause us to slow or stop. By the time her legs become leaden, Felicity has notched up a VO₂ of 35.4, which for a woman in her 50s puts her in the “excellent” range.

Jackson finishes at 43.6 – as a man in his 30s, he’s hovering between “average” and “good”. What do these differences mean? “Both of you are fit, but it comes down to the fact that it’s all relative to our own age and sex,” says Levinger. “What helps is to know where your aerobic fitness is at and where it should be for your life stage.”

There are other, less high-tech, ways to test aerobic fitness. Many Australian schools have required students to do the (gruelling) shuttle run, or “beep test”, as part of physical education. Participants run back and forth 20 metres to beat the beeps that progressively sound at shorter intervals. (The AFL scrapped this test of draftees in 2017, saying it wasn’t helpful in assessing fitness for team sports, which involve more stop-start action, and instead now uses a test that incorporates breaks.) A less intense version requires participants to walk back and forth 20 to 30 metres as many times as they can for six minutes. “We know that people who cover less than 450 metres are at a lower fitness level and higher risk of chronic disease,” says Levinger.

But cardiovascular fitness is only part of the puzzle. As a general indicator of upper-body strength, Levinger asks us to squeeze a dynamometer as hard as we can. Felicity clenches 27 kilograms with her left and 27.5 with her right (16 kilos or less indicates low muscle strength for a female.) Jackson squeezes 38 kilos with his right hand and 36 with his left (not bad, given 27 kilos or less is considered low for a male), but our photographer, Paul, who regularly lifts weights, squeezes a staggering 57.5 kilos with his left and 48 with his right. (A lapsed jogger, he confesses he’d be less than impressive on the cardio test.) We also test lower-body strength on a leg press, where Levinger aims to have people capable of pushing twice their body weight.

‘To maintain where you are now, you will have to work harder and harder. But the slope of the downhill is slow if you control it.’

Ultimately, a good fitness test gives a holistic picture of strengths and weaknesses. Felicity, who swims and plays tennis (as head-clearing resets after busy days at a desk), avows a healthy lack of interest in exercise involving monotonous repetition: lifting weights. “I’m not into gyms.” Levinger reminds her that a little work now will pay off in the future, and it doesn’t have to be in a gym. Is it all downhill from here then? she asks. “To maintain where you are now, you will have to work harder in the future,” he says. “But the slope of the downhill is slow if you control it.”

For Jackson, a runner, weights training could help too: he recently had an injury mid-marathon, and bolstering his hips, glutes and leg muscles might stop the injury from recurring. Also, says Levinger, “We know that endurance training alone for most people will not substantially affect their muscle strength. Bone needs stress in order to increase bone density.”

The one thing Levinger doesn’t calculate is BMI or body-mass index, which gives indications of obesity. “We don’t know whether this is mostly muscle or mostly fat,” he says. “We can have two people who are the same weight and the same BMI. One of them will be with a very high percentage of fat, and they will be at a very high risk of diabetes and very poor fitness level. And the other person is a bodybuilder.” If obesity is a factor, he says, he will measure someone’s waist circumference or use a scan called DXA (Dual-Energy X-ray Absorptiometry) for future comparison to show improvement after exercise.

How do you get fit (and stay fit)?

Roman gladiators trained ahead of contests, ancient Chinese cultures championed martial arts, and male citizens in Ancient Greece went to gymnasiums, from the Greek gymnos, meaning “nude”, which, incidentally, was how their exercise was done, to encourage appreciation of the body.

Eugen Sandow, a 19th-century German bodybuilder, modelled his physique on those Ancient Greeks, with some vaudeville: he’d break chains and flex for crowds at strongman shows. In the ’50s, American Jack LaLanne, a self-confessed former junk-food addict, reinvented himself as a fitness guru for television audiences and was eulogised 60 years later as “the founder of modern fitness”.

By the ’80s, Jane Fonda was pioneering a new generation of women’s exercise (and leg warmers) in the home via workout books and videos. “She was focused on a really sensible exercise routine,” says Hayes, “beginning with a warm-up, going to high-intensity aerobic workout and then a cool-down and incorporating yoga. She designed routines for people for different stages of life, for pregnant women. They didn’t have to go to a gym, they didn’t have to hire a babysitter, and they could wear whatever they wanted.”

Fonda’s formula also combined several components of fitness in single workouts – cardio, body weights and flexibility. Today, high-performance manager Matt Hornsby says that “a weekly structure that allows you to tick off those different fitness components is a good starting point”. “But then you’ve got to find nuance in that, based on what your own goals are, ambitions and your strengths and weaknesses.”

‘It’s a bit like a golf handicap ... small investments regularly improve your handicap pretty quickly.’

Once these have been established with a trained expert, says Hornsby, the best way to build fitness is through “progressive overload”. “The problem of jumping into more extreme programs off a low base is that whenever the gradient is steep from where you were to where you want to get to, your risk of injury increases,” he says. “Positive stress of training needs to be progressively overloaded so your body adapts. And the human system is fantastic at adapting to that stress, but you just need to layer it over weeks and months.”

This might involve overcoming some discomfort as the body adapts, says Melissa Arkinstall. “It’s evolution. The body tries to prepare. You’ve asked it to do something it’s not accustomed to, or it hasn’t done previously. This often leads to little micro tears in the muscle and minor soreness, but they’re not to be feared – they trigger a repair process that leads to better muscle performance.”

The gains can start to happen within just a few weeks. Says Hornsby: “It’s a bit like a golf handicap; if you’re way back and haven’t done much and have a pretty average handicap, then small investments regularly improve your handicap pretty quickly. But as that handicap comes down lower and lower, the gains don’t seem as significant.”

Still, even once the immediate benefits are less apparent, the long-term benefits keep accumulating. “I see fitness like superannuation in that you have to invest in it over time, and it pays you back.” Says Arkinstall: “Once you have established a base level of fitness, you can just tap into it. That might be two to three sessions a week.” And keep going – it’s true that if you don’t use it, you lose it. “The body will start to down-regulate: it will start to turn things down if they are not used, within hours.” In fact, in many of the sedentary hours of our lives, the body is adjusting itself for efficiency – muscle atrophies, our cardiovascular system deconditions and our metabolism slows.

Australia’s physical activity guidelines say adults should do 2.5 to 5 hours of moderate physical activity each week (a brisk walk, gardening, swimming) or 1.25 to 2.5 hours of vigorous activity, such as running or a team sport such as soccer or volleyball, including muscle strength training. For people 65 and older, the guideline is 30 minutes of moderate activity on (preferably) all days of the week. Canada follows 24-hour movement guidelines, which provide a picture of what a day ideally involves: exercise that accumulates to 150 minutes a week, between seven and nine hours sleep at consistent times, and no more than eight hours of sedentary activity a day.

Meanwhile, Levinger is trying to move away from the word “exercise” which can carry negative associations. “Instead, we talk about incidental physical activity – when you’re going shopping, for instance, don’t try to find the closest car park – try to park 10 minutes away from the shopping centre. So you do 20 minutes of physical activity while walking there and back without thinking about physical activity.”

Deakin’s David Scott advocates “exercise snacking”, which could be four 10-minute sessions done throughout the day. “A colleague of mine keeps some weights by his desk, and just when he’s got a 10-minute break in the day, he’ll pick those up and lift them for 10 minutes. But for older people, we’ll often just suggest they do 10 rises from their chair; get up and get back down, and get up and get back down as fast as you can.”

‘I think while he swam he would think, and he would go over writing in his head.’

Even though his research is into muscle strength, Scott struggles with motivation for himself, but he’s seen the difference simple weights training has made for older clients. “They’re just getting so much more out of life at a time when they’re retired, and they’ve got the opportunity to do things and spend time with grandkids, go travelling, and that can get taken away from them quicker than it should.” While he played footy in his youth, he’s fitter now than he’s ever been, at 42, running 70 kilometres a week.

“The time that I kind of just get out there, plodding on the pavement but thinking things through, working things out in my head that I’ve struggled with at work – it makes such a difference. When you find that exercise that you enjoy, it’s amazing how it impacts you.”

Whether it’s skipping, dancing, jogging or squash, the most important thing is we find exercise we will keep doing. For some people, it helps to do an activity with others to stay committed. The goals of the activities don’t have to be focused on the long term. Hayes recalls how he and Oliver Sacks (who died of cancer in 2015) would swim together. “He would swim a mile three times a week at a pool nearby here in the West Village. And at first, I would just go with him and maybe work out in the gym while he swam.

“But, eventually, he persuaded me and I got a swim coach who sort of helped me brush up my technique, and then we would swim together, and that became part of our life and part of our relationship,” Hayes says. “I think while he swam he would think, and he would go over writing in his head. And in the earlier days, when he would swim at lakes, he would have a pad of paper and a pen on the dock, so if he suddenly had a thought while he was swimming, he would jot it down on the pad, and it would get all wet, the ink would smear.”

For fun summer reading, buy the new anthology from the Explainer desk at The Age and The Sydney Morning Herald. Why Do People Queue for Brunch? The Explainer Guide To Modern Mysteries is packed with astonishing facts and sizzling barbecue banter. In bookstores now.