I am not sure I like my elder brother any more. If I run down humid, concrete Singapore paths, he lopes along the moors of Devon where he lives. As he crosses the uneven land, he sees foxes, deer, rabbits, semi-wild Dartmoor ponies, landscapes and no people. On grey, misty days he feels as if he's on the set of The Hound Of The Baskervilles. I told him he's a howling show-off.

We were talking exercise - brothers compete even across the oceans - and ways to sweat off worry in a time of Covid. Nothing illustrates endurance better than the endless road. In a time of sickness this is where we clear the mind and feel alive. As my friend Karen, a regular runner who is now even more consistent, put it perfectly: "I used to run for vanity, now I run for sanity."

When I look out of my window I see a stream of huffers and puffers, patrollers and amblers, striders and cyclists. Yesterday, a grey-haired walker with a white umbrella strode down my lane. He appeared to clench his fist and flex his arm and perhaps he was only loosening up. But it almost looked like he was brandishing his fist at an unseen enemy. By walking, you see, he was taking on the virus.

People exercise to shed calories, find calmness and show off on dating websites. But it also settles the nerves, ensures discipline, builds resolve and demands focus, so many of the things we require to arm ourselves in a crisis. The greatest competitions anyway, athletes will tell you, are with the self. We can't control the virus, but we can our responses.

A 59-year-old friend in India, who I speak to on most days, converses while walking down the corridor of her flat. On this short runway she has taken healthy flight. Every day she walks 10km and then recites her weight loss as if it is an Olympic triumph. It is if you consider that pre-Covid her exercise was restricted to repeated lifts of a beer glass.

The virus has awoken people and now conversations are littered with throwaway lines about Vitamin D, almond milk and homemade gyms. One friend even hails his exhausting workout involving broom and mop. The heft of dumbbells is casually thrown into chats, barre burns are discussed and Hasfit argued about. I used to think Tabata was a type of dish till I was better educated.

Sweat has become a useful weapon and fresh air an inviting medicine. Even habitually indoor people are tiptoeing into the outdoors. One colleague, wedded usually to her screens, has recently acquired a cycle to explore this island and herself. To buy the cycle, as opposed to renting it, ensures it is a commitment not a lark.

Another colleague, partial to dim sum, finds herself more often in her garden, digging and pruning, her hands deep in mud, vegetables, worms and roses. This is her challenge and from physical effort, in whatever form, is built psychological armour. We aren't immune, but we can be resolute.

The virus is uncompromising and humankind is currently fatigued. We're a species in search of second winds and we learn about resistance when we're out on our runs and walks. Push, we tell ourselves, one more step, one more kilometre. It is the inner voice which delivers us to small victories.

Some days I see cyclists, low on their bikes as they ascend a slope on Yio Chu Kang Road, their teeth bared in effort. It makes me grin because it looks like the familiar burn of lactic acid. They're going to beat the slope, again, and, like anything else, persistence is built from habit.

The more often we lace up our shoes, the hardier we feel. After months of no tennis, to play again was to remember how invigorating it felt to be tested. We don't know our limits till we strain against them. It is training that comes in good use because the virus, like a bully, is pushing us further and further outside our comfort zones.

As I write this both my calves have ice packs tied to them, for I was trying to run faster on a court than is officially recommended for my age group. But I understand my soreness because I find this time on the court so precious. None of us know if the courts will be locked again and so it feels like every session has to be squeezed for every bit of joy. My partner is getting more I think, for he is hammering me.

As humans meet virus, sport has a small role. If nothing else, we often learn that we're stronger than we think. There is - like in a football game - no guarantee of victory, but there is great benefit to be found in the effort. It doesn't matter where you are, a sweltering city or the rainswept moors, every step taken or pedal pushed down has the same value.

They are, in small ways, all acts of defiance.