When Ms Cherie Sim, 29, joined a fitness class described as a 10-minute plank last month, she thought it would be a workout comprising variations of the plank pose.

Instead, the trainer challenged participants to hold a forearm plank for 10 straight minutes. Sweating and shaking, Ms Sim lasted half that time, a personal record.

"10 minutes felt impossible, but I wanted to try," says Ms Sim, who is the co-founder of content media agency and travel publication The Travel Intern.

So she came up with a challenge - starting with 30 seconds, she would hold a plank for 15 seconds longer every day until she hit the goal.

Three weeks later, Ms Sim is well on her way to reaching her target, with more than seven minutes on the clock.

Under circuit breaker measures aimed at reducing the number of coronavirus infections in Singapore, gyms have shut and exercise regimens have been confined to the home.

Besides online classes, some have taken up social media fitness challenges to spice up their daily workouts. This could involve more repetitions every day, increasing the length of an exercise or doing a one-off challenge with as many repetitions as possible in a set time.

Even brands and organisations are now in on the act. The Republic of Singapore Navy, for instance, last week posted an Instagram video of 50 people from the Naval Diving Unit doing as many push-ups as possible in a minute, with many accomplishing between 60 and 80.

For aspiring challengers, the right form is important. While it may be tempting to chase the numbers, Ms Sue Suharni, principal master trainer at boutique gym Fit 247, recommends quality over quantity.

"If you do too many repetitions or do them incorrectly, you may sustain chronic injury," says Ms Sue, who recommends modifying such challenges to one's own fitness levels. For instance, one might increase the number of repetitions on a weekly, rather than daily, basis.

But she adds that when done correctly, fitness challenges are beneficial as the increase in intensity helps build muscle strength and prevent the risk of plateauing.

Actor and host Allan Wu, 47, has been doing just that for the past month. He launched the #Plus10 push-up challenge at the start of the circuit breaker, every day performing 10 more than the previous.

"It is about going above and beyond what I can usually do. This extends beyond push-ups to my philosophy in life," says Wu, a self-declared fitness buff who used to incorporate about 100 push-ups as part of his gym warm-up prior to the circuit breaker.

He did 450 push-ups on Friday, but the record did not come easy. On his Instagram account, Wu (@wulander) makes no attempt to hide his difficulty as he struggles through the last few repetitions each day.

"I want to be transparent about the strain and intensity of the process. Everyone has the ability to be in better shape, but you have to put in the work," says Wu, who is often shirtless in his videos.

Critics have charged that these challenges are little more than an exercise in vanity. In March, Indian film director Farah Khan, who has more than two million followers on Instagram, called on celebrities to stop "bombarding" their followers with workout videos, adding that most people have bigger concerns during a public health crisis.

But for those lacking a gym buddy, social media fitness challenges offer the support of a community - people who spur you on with likes, tags and encouraging messages.

Wu says that although there are days he feels sore and unmotivated, seeing others take up the challenge is enough to get him off the couch.

Fellow challenge participants include actors Pierre Png and Maxi Lim, professional race driver Yuey Tan and even his son Jonas, 14, from his previous marriage to former actress Wong Li-Lin.

Ms Sim (@cheriesyw) agrees. "I sometimes plan to take a day's rest, then someone will tag me in his or her plank challenge. It reminds me to keep going because I was the one who started this," she says.

One person who has joined her is secondary school teacher Joelle Lim, 41, who taught Ms Sim when she was a student.

The two women share tips on how to distract themselves while planking, such as by watching videos, listening to podcasts and talking to themselves.

Ms Lim, for instance, verbalises daily reflections while holding a plank.

"I use the time to let go of what didn't go well, thank myself for pushing through certain challenges and appreciate the effort I have invested in myself and in other people," says Ms Lim, who is married to an offshore diver in his 30s.

The distraction paid off. This week, she managed to hold a forearm plank for a whopping 12 minutes.

Impressive figures aside, the real value of fitness challenges lies in keeping active, especially when cooped up at home.

That was what Dr William Wan, 73, wanted to convey when he posted a video of himself doing push-ups on Facebook this month.

Dr Wan, who is general secretary of the Singapore Kindness Movement, suggested that people do at least five push-ups every day and add one more every alternate day.

The video has been shared more than a hundred times, which has surprised Dr Wan, as he calls social media challenges a "young person's game".

He says his goal was merely to encourage his friends to exercise.

Under the circuit breaker, he works out about five to six times a week for close to an hour each time and does about 60 push-ups as part of his routine.

"As we get older, our muscle mass will shrink and our bones grow more brittle. Exercise helps to slow this down," says the father of three, who has four grandchildren. He lives with his wife, 78.

Dr Wan, who last year published the book, Through The Valley: The Art Of Living And Leaving Well, adds that staying active is important to leading a full life.

He says: "You need to be physically fit in order to relate to people, process information, build relationships and serve the community. As long as I can live until tomorrow, I want to live well and to the fullest."