It was an odd letter for the Guardian's agony aunt to receive. "My husband of 10 years has become obsessed with fitness. He's at the gym twice a day: swimming in the morning and again after work for up to two hours. Our living room is cluttered with dumbbells and our small kitchen has been overtaken by tubs of protein. He doesn't have the time to help me around the flat." Should she leave him?

Traditionally, wives have complained of their husbands lazing in front of the TV or disappearing to the pub instead of doing their fair share of housework. Now, as the letter suggests, things have gone to the other extreme.

It is not just men who have become obsessed with exercise. With gyms closed by the lockdown, we can see just how many people of both sexes are in thrall to it. The streets and parks are filled with Lycra-cladA light, stretchy material popular with runners and cyclists. In the US, it is usually called spandex - an anagram of "expands". figures jogging and working out, often taking remote instructions from instructors on their smartphones.

The benefits of exercise are well known. It is good for your heart, lowers your blood pressure, improves sleep, and strengthens your muscles and bones. It also helps you keep at a healthy weight by burning calories and raising metabolismThe chemical processes within the body which produce energy. It derives from a Greek word meaning "change"..

But experts worry that many fitness fanatics are narcissists who care more about their appearance than their health. A survey by an American eating-disorder charity found that 48% of women took exercise mainly because they wanted to look thinner.

Obsessive exercising often results from an unbalanced state of mind. Another survey found that 80% of marathon swimmers suffered from psychological problems. The gym is a common refuge for people who are in emotional turmoilA state of great confusion. The word was originally a verb meaning to agitate..

Another letter to a newspaper offers an alternative perspective. "I walk and, yes, I garden, but only for pleasure; never in obedience to a fashionable mania," wrote Edna Thomas to the Sunday Times. "I like steak and chips, chocolate digestive biscuits, thickly buttered toast, strawberries and cream. I take no medication. My weight, blood pressure, heart, and lungs are all in excellent order [...]. I find super-exercisers boring and super-muscular bodies somewhat repulsive. I am 92 years old."

Some people argue that anything which encourages people to keep fit is a good thing. One of the greatest threats to health is a sedentary lifestyle, which often leads to obesity and diabetes, costing the NHS a vast amount of money. Computers have become so much a part of our lives that we need an alternative to sitting in front of the screen, and nobody should complain if a gym supplies that.

Others say fitness fanatics are self-obsessed people with no consideration for others. Their routines rule their lives, and they make those who cannot emulate them feel inadequate. We only need a moderate amount of exercise to keep healthy - too much will damage the body in the long run. It is also a poor use of energy: the same time and effort would be much better spent on building something.