Perhaps even more important is the impact of exercise on our mental health, and how it has the power to transform mood from listless and lethargic to relaxed and focused. "The positive impact of exercise is long established," says clinical health psychologist Dr Vincent McDarby, a member of the Psychological Society of Ireland. "It works on stress, anxiety and depression. It helps us relax, and improves self-confidence immediately, because the moment we start exercising, we view ourselves as healthier."
It needn't be anything madly strenuous. "Adults need at least 30 minutes of moderate intensity exercise five times a week," says Tara Curran of the Irish Heart Foundation. "This should be all year round, not just in lockdown. Regular moderate exercise helps the heart, plus lung capacity, muscle strength, balance, weight management, and mental health, by reducing stress and anxiety." For under 18s, it's 60 minutes, and moderate intensity can be a brisk walk - anything that warms us up and makes our heart beat a bit faster.
There are broadly three types of exercisers - the keen, the moderate, and the avoidant. When it comes to boosting your immunity, being a moderate exerciser is the most effective; a bout of strenuous exercise actually reduces our immunity for three to five hours afterwards.
"Start small," says Professor Niall Moyna of DCU's School of Health and Human Performance. "Now is a wonderful time to start. The most important thing to remember is that anything is better than nothing."
A report in The Lancet from last week shows how more severe Covid-19 symptoms are linked to obesity in younger age groups.
This does not mean, however, that we freak out and set ourselves up to fail with crazily unrealistic targets in a bid to slim down.
"We have all gone through significant day-to-day lifestyle changes," says Dr McDarby.
"Lots of avenues of pleasure have been closed off, and our healthier habits may have been put on hold as we deal with the situation in front of us. The easiest avenue may now be Netflix and ice cream."
Which is why the longest journey at the moment can be from the sofa to the front door. When it comes to doing things that require effort, we tend to think in terms of motivation followed by activation, but actually it's the other way around.
"That first step is overriding the negative voice," says Dr McDarby. "That's the hardest part, because once you have activated yourself, the positive mental feedback becomes your motivation."
It's just that initial push that's the hard part. Which is why reminding yourself that any exercise is better than no exercise is vital.
"It's really important to be compassionate to ourselves during lockdown," adds Dr McDarby. "Take small steps, so that change happens incrementally, until it is ingrained in your everyday life, which means it can be maintained long term."
Feeling sluggish on the sofa, or feeling claustrophobic and hemmed in, or both, can provide an intrinsic driver to get out and move, rather than unreliable external motivators like watching shiny athletic people on social media running marathons, or relying on your willpower, which is finite, and in very short supply at the moment.
Listen instead to your own inner wisdom and self-knowledge. Like knowing you'll feel good after a walk or a bike ride or a dance. And then commit to whatever it is you know will make you feel good.
"I know I'll turn up if I've committed to an online class," says chartered psychologist and columnist with Health&Living, Allison Keating.
"So at the moment I'm joining exercise groups on Zoom, because committing externally helps with my motivation. I do it even though I don't want to, and my reward is feeling good afterwards - I love the feeling of it being over."
Even better is getting outside, where you can combine movement with being in nature - again, the link between nature and improved mental health is well documented. But if you can't get out, then dancing manically around your kitchen to the Chemical Brothers will also make you feel great.
In her book The Four Tendencies, US author Gretchen Rubin explores the difference between inner and outer expectations (inner would be maintaining your own New Year's resolutions, while outer would be observing traffic regulations or work deadlines).
She applies these expectations within four sets of character traits she has identified as Upholder ("I do what others expect of me and what I expect of myself"), Questioner ("I do what I think is best, according to my judgment. If it doesn't make sense, I won't do it"), Obliger ("I do what I have to do. I don't want to let others down, but I may let myself down") and Rebel ("I do what I want in my own way. If you try to make me do something - even if I try to make myself do something - I'm less likely to do it").
Within these four archetypes is a mixture of resisting and meeting our internal and external expectations.
Identifying where you are at psychologically, so that you can work with yourself via self-praise and self-encouragement will go a long way. Far further than berating yourself for not doing enough, or setting yourself the kind of unrealistic targets that you cannot reach, and then beating yourself up. "You do not have to be running 5k," says Dr Vincent McDarby. "You just need to make small, sustainable changes."
⬤ Commit externally to an online exercise session that suits you, that you will enjoy, and that works for your fitness/unfitness level.
⬤ Put it in your diary, as though it is a work commitment
⬤ Do it at roughly the same time every day - mornings are best, but anytime is good
⬤ Focus on how you'll feel when it's over
⬤ Be open and curious about trying new things - you may surprise yourself
⬤ Remember that all exercise counts, indoor and outdoor
⬤ Do it even though you don't want to
⬤ If you don't do as much as you intended, still praise yourself, as you did some
⬤ Note your change in mood before and after