It is good news for the celebrity fitness DVD industry, if no one else. More than half of the women in Britain are too embarrassed about their bodies to exercise in public, a survey suggests.

Nine out of 10 women over 30 have low self-esteem and poor body image, which forces many of them to exercise indoors or go running in the dark. The findings, by the mental health charity, Mind, are particularly unfortunate because outdoor exercise is known to be far more effective at improving mood and mental wellbeing than an indoor workout.

“We all know walking, cycling, even gardening are good for our mental health,” said Beth Murphy, the head of information at Mind. “However, for many of us, exercising outdoors can be incredibly daunting, especially if you are already feeling low and your self-confidence is at rock bottom.

“At these times you can feel like the only person in the world experiencing this, but our research highlights that far from being alone, 90 per cent of women are in exactly the same boat. It is time we start talking about how exercise makes us feel. We urge women to take the first step, invite a friend on a nature date and begin to support each other in taking care of our mental wellbeing.”

More than half of the 1,450 women surveyed said they exercised very early in the morning or late at night, solely to avoid being seen by others. Nearly two-thirds said they exercised in a location where they were unlikely to bump into anyone they knew, and a similar proportion said they wore baggy clothing to conceal their figures.

Gym classes are also a no-go area, it seems. Two-thirds of women said they did not think they would be able to keep up in an exercise group, that they would look silly, or that the women there would be “cliquey” and unwelcoming.

Sixty per cent were nervous about exhibiting themselves while sweaty, and were worried about their “wobbly bits”, passing wind or going red. Only 6 per cent thought they would be likely to make new friends.

Mind’s researchers found that women were acutely aware of the importance of keeping fit and active lifestyles, and therapists were increasingly prescribing outdoor exercise as a way to fight stress and depression.

But the charity said that, rather than exercising, women reported that they were more likely to spend time eating comfort food (71 per cent), listening to sad music (32 per cent), spending time social networking (57 per cent), going to bed (66 per cent) or finding a way to be alone (71 per cent).

Mind, which offers advice and support people with mental health problems, has launched a “Feel Better Outside, Feel Better Inside” campaign to encourage women to start talking about outdoor exercise, and to encourage friends to exercise outdoors together.

Case study: ‘I always felt so self-conscious and anxious’

Tracy Bell, 38, lives in Bedford and has suffered from occasional bouts of depression for 10 years

My GP prescribed me gym membership as therapy. I went to the sessions because I felt I had to, but I hated every minute and stopped as soon as I could.

I went time after time because it was my prescription, but I felt so self-conscious and anxious. The exercise environment is just so cliquey – I would never have made any friends.

Everyone there was completely different to me. They were thinner, fitter and better at exercise. To make things better, I would time my trips really carefully. I would make sure I went mid-morning, so I missed the morning rush and then the lunchtime rush, too – just to make sure I would be seen by as few people as possible.

I’ve been asked if I talked to my friends about how I felt, but there’s no way I could. They are so much thinner and more sporty than me.

A lot of my friends who live near me are a little bit younger and I just know they wouldn’t understand. I don’t know how to put it – I guess I feel like I must be the only one who feels like this.