A better understanding of what happens to our bodies when we get fitter can unlock ways to speed up the journey – and it might be simpler than you think.
Watching an athlete at their peak is thrilling. Fulfilling one’s own athletic potential, not so much. Getting fit is hard and painful – or so we assume.
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But that isn’t necessarily the case. In fact, research shows that anyone just starting to exercise more than they are used to will see improvements surprisingly quickly, regardless of the workout they choose. Better yet is the discovery that there are ways to speed up the fitness journey.
The key to improving fitness is, in essence, simple. You need to exceed your “habitual load”, which is a fancy way of saying doing more activity than you are accustomed to. This will stress your body and force it to adapt.
When it comes to starting cardio exercise as a beginner, “one of the first things that happens is you get more blood volume”, says Abbi Lane at the University of Michigan. Within 24 hours of working out, this increases by up to 12 per cent due to water retention, which increases the amount of blood plasma, boosting the amount of oxygen that can be supplied to the muscles. After two weeks of training, peak blood volume is normally reached, which is about 15 to 20 per cent higher in athletes than in sedentary individuals.
Energy-producing structures within our cells called mitochondria become more numerous and efficient around this time as well. Small blood vessels known as capillaries begin rapidly proliferating within muscles, too, improving the body’s ability to deliver oxygen to tissues. One study found that capillary density expanded by about 20 per cent after two months of a cycle training programme.
These shifts enhance the maximum rate at which the body can use oxygen, a measure known as VO2 max, says Stuart Gray at the University of Glasgow, UK. Changes in VO2 max typically occur around six to eight weeks into training. By the third month, it can improve by approximately 10 per cent, he says.
Getting stronger
Muscle also adapts rapidly. A single session of strength training increases the activity of genes within muscles involved in regulating inflammation and removing waste products that accumulate as a result of the stress of exercising. It doesn’t take long to build muscle strength either, at least if you are a beginner. “Everyone gets stronger in their first three weeks because your nervous system learns how to talk to your muscles better,” says Lane. With repetition, the nerve signals from the brain get quicker, and muscles become better at responding to them, generating greater force more rapidly, says Gray.
Exercising also builds brawn by tearing muscle fibres, allowing them to build back stronger. In a sense, you literally become “ripped”. This takes a bit longer, though, so the greatest improvements in muscle size and strength don’t happen until about eight to 12 weeks into training.
All of this suggests that exercise should feel a bit easier within two to three months of your first workout. But several factors mean this varies from person to person. The most significant influence is genetics. Our genes determine about half our aerobic fitness, says Lane. “Some people, no matter how much they train, their VO2 max won’t shift very much,” says Gray. “Then, you’ll get the very annoying people that will do the same training as you and their VO2 max will fly off the charts.”
Age is another factor, with younger people adapting to exercise more quickly than older adults. Prior physical activity makes a difference, too, as people who have previously trained are able to rebuild muscle faster than those who are just starting out.
A wide range of exercises can improve fitness within a few months, provided they are done three to five times a week for about 30 to 60 minutes. For instance, 12 weeks of endurance training such as cycling increased muscle mass by 7 to 11 per cent, roughly the same as a strength training programme of the same duration. However, one regime seems to trounce all others in terms of getting fit quick – both from an aerobic and strength perspective – by stressing our physiology in just the right way to induce maximal adaptation.
High-intensity interval training
High-intensity interval training (HIIT) involves exercising at near maximum effort in repeated bursts of up to a minute, with short rests in between. This regime was devised in the 1990s by Izumi Tabata and his colleagues at the National Institute of Fitness and Sports in Kanoya, Japan. They showed that a 4-minute workout, with repeated cycles of 20 seconds of intense work then 10 seconds of rest, done five days a week for six weeks resulted in greater aerobic improvement than moderate, hour-long workouts done over the same time frame.
Since then, many trials have confirmed the power of HIIT. “If you want a quick increase [in fitness] over four to six weeks, purely intervals would do the job,” says Lane. The key is working as hard as you can during the intense intervals. Just six HIIT sessions over two weeks significantly improves VO2 max and endurance capacity, but, remarkably, a 2021 study found similar improvements could be achieved if these HIIT sessions were squeezed into a five-day period.
Adam Sharples at the Norwegian School of Sport Sciences in Oslo says beginners should start with two to three HIIT sessions per week. You can intersperse these with longer-duration endurance activities, such as jogging or swimming, to further boost results, he says. Once you notice that your strength has plateaued with HIIT, you can add two or three full-body strength-training sessions, says Lane.
However, the best exercise is ultimately the one you will be able to stick with, not necessarily the one that leads to the quickest improvements. “We sometimes get in the weeds with what is the perfect plan, but I think for most people, we just need to get out there and get moving,” says Gray.
The trick is to continuously challenge yourself. If you do, you may be surprised to discover your own peak performance.