Exercising days, weeks and months: How your body changes

But don’t let that dissuade you. Robergs stresses the importance of reintroducing intense exercise back into your routine because it offers enormous physical and mental health benefits.

From the moment you start exercising again, your body begins complex processes to rebuild its fitness, and while change is slow, it’s continuous, and worth lacing up for the long-haul for.

On the day of exercise

Exhausted, breathless and feeling clumsy? That’s OK. The first workout is unlikely to leave you feeling as accomplished as you might have hoped, Robergs says.

“You’ll have the perception that generally speaking things were much harder to do,” he says. “There’s a lot of physiology that goes into that movement.”

First, Robergs explains, your brain is doing a lot of work to coordinate all these new nerve patterns to your muscles. “There’s a lot of mental effort that’s very subconscious,” he says, adding it’s why you have to concentrate when exercising.

“It’s amazing how rapidly the muscles adapt … They become stronger and more tolerant.”

Associate Professor Rob Robergs, accredited exercise physiologist, QUT

When you take a break from working out, your body shrinks muscle fibres and breaks down blood vessels in the muscles that are no longer being used. “The body is always trying to conserve as much energy as possible,” Robergs says.

It means when you return to exercise, you’re fatigued because high demand is being heaped onto your heart and lungs to increase blood flow through your contracting muscles, but your body has become less effective at doing this.

The upside? As your body pushes to oxygenate the muscles, this stimulates surrounding tissue to again start synthesising those blood vessels and muscle fibres you’d lost.

Accredited exercise physiologist Sam Rooney, from Sydney’s Ion Training, says you’ll be spent even if you’d been exercising in lockdown but are introducing a new routine. “It will help but it’s not the same, you’re still challenging your body in a completely different way.”

In the day after

The main thing you’ll notice is aching muscles when you wake up the next day. Where the pain is will depend on your workout, but it’s possible that stairs won’t be your friend for three or four days. That’s because lengthening and contracting your muscles can cause microscopic damage, resulting in delayed onset muscle soreness, also known as “DOMS”.

But it serves a purpose, Robergs says: “It’s an unfortunate part of the muscle’s response but it does improve the muscle structure and function.”

It only becomes a concern with severe pain, as it means you’ve done too much too quickly. “Barely being able to sit down [the next day] means you’ve overdone it,” Rooney says.

But usually, it’s nothing to be alarmed about, Robergs says, and the next time you work out, you’re “incredibly unlikely” to be as sore again.

“It’s amazing how rapidly the muscles adapt,” he says. “They become stronger and more tolerant.”

Rooney says he generally recommends exercising through muscle soreness. “Ironically the best way to get rid of that soreness is with movement … as long as your movement is not compromised.”

Your resting metabolic rate also increases after training. Your body consumes more energy for muscle repair, therefore burning more calories when not exercising. “One study showed that after 45 minutes of vigorous cycling, participants experienced an approximately 40 per cent rise in their metabolic rate for 14 hours,” Rooney says.

Robergs says another immediate effect you can expect after exercising is reduced appetite. “Most people think that if you exercise and expend calories, you’ll get really hungry, but if you’re hungry before working out, you’ll find that goes,” he says. “[Put simply] the hormonal response to exercise and the energies you expend reset the brain and sense of hunger.”