The problem of older children not getting enough exercise is well-documented. That experts now fear the very youngest members of our society are also losing out is not so well known.
Changes in society, in lifestyles and in the nature of education for the under-fives, are all conspiring to restrict physical activity at this crucial stage, they believe, storing up potential health and social problems for later life.
Quantifying the problem is difficult. Comparative studies are not yet possible, as no research was done 20 or 30 years ago against which to measure current levels of physical activity. Equally, children in this age group are less easy to monitor than older ages. However, a trend does appear to be emerging that is difficult to ignore.
Neil Armstrong, professor of health and exercise sciences at Exeter University, has studied primary-aged children and believes the problems start early.
"Children aged eight and over are nowhere near as active as they should be," he says. "We believe that the seeds of low-level activity among these older children are being laid down at a very early age." The problem is particularly acute in girls, where again the patterns are laid down in the pre-school years.
"There is no question that children were not doing enough exercise," says Peter Warburton, lecturer in education at the University of Durham. His study of four to 11-year-olds, conducted with Mike Sleap, lecturer in education at Hull University, found that four-year-olds displayed the lowest levels of "vigorous activity" of all the age groups. Girls were far less active than boys. None of the age groups displayed the recommended levels of sustained physical activity.
Look for the reasons and again, the patterns found in the lives of older children hold true for the under-fives. The increasing use of the car, the effect of TV, high-rise housing, and restrictions on children's outdoor play due to fears for their safety all combine to keep them indoors and inactive.
But some specialists also point to changes in the pre-school learning environment, arguing that these are also restricting the under-fives. In particular, there are fears that opportunities for outdoor play are being threatened by deregulation and the introduction of pre-school vouchers.
The relaxation this month of national minimum space requirements in maintained nursery schools has come under bitter attack from the British Association of Early Childhood Education. It claims that the changes will allow nurseries to be set up without playgrounds and no statutory minimum for teaching space. Space requirements in private nurseries come under the Children Act, which recommends that outdoor play space should be provided, but local authorities are entitled to interpret the guidance flexibly.
Pauline Wetton, lecturer in education at Durham and author of PE in the nursery and infant school, studied 132 three and four-year-olds in the North-east. She has little doubt that in nursery schools at least, children are getting less exercise. "We are very concerned that these children are not getting as much chance to be outside and play, to use their bodies in physical activity," she says.
The problem may in part be due to unsuitable facilities. Children in primary-school reception classes do not always have a separate outdoor play area. "If the weather is bad, there is sometimes a reluctance by heads to let them use the hall." She also feels that children have less opportunity for free choice in the pre-school timetable, which for many, would include outside play.
"Children used to have open access. There could be up to 100 minutes of time when they were more or less free to choose what they did, including playing outside." Now they tend to be restricted to an organised 20 minutes, at a time of the adult's rather than the child's choosing.
Pauline Wetton has observed an increase in teacher-directed, table-top activities. "There is definitely a trend towards less gross motor and locomotor activity, and towards more fine motor activity in nursery schools," she says.
This trend may not be helped by increasing pressure on nursery schools to show evidence of educational achievement. Desirable outcomes, published last month by the School Curriculum and Assessment Authority, sets goals in six areas of early-years learning. One of these is physical development, which Pauline Wetton feels is crucial. "Physical and intellectual development are so closely linked at this stage. Until he or she has got equilibrium of body, a child can't sit still and learn to write."
Low levels of physical activity in children cannot be directly linked to health problems, according to Neil Armstrong, but are likely to be storing up problems for later life. "It is highly unlikely that an inactive child will turn into an active adult," he says, risking high blood pressure, obesity and heart disease. Studies have found that Western children have relatively high cholesterol levels by the age of two and an inactive lifestyle does nothing to help.
Low physical activity as a child also increases the risk of osteoporosis in later life, as bone development occurs during the first two decades. "If an individual does not experience weight-bearing activity during that time, less bone density is stored for adult life, leading to an increased risk of osteoporosis, particularly for menopausal women," according to Professor Armstrong.
There are social consequences too. Janet Moyles, a lecturer at Leicester University, has studied children's play for years and feels that diminishing opportunities for physical play effect their social development. "A child who is touched or knocked accidentally may respond with aggression because he or she does not know any other way if they haven't experienced rough and tumble play."
Children need to take part in activities such as climbing in order to learn how to take risks safely, she believes. "Risk taking is a huge part of people's lives and the increase in vandalism or joy riding may be because young people are increasingly restricted in opportunities for active play in their early lives."
Adults are recommended to have 15-20 minutes of sustained physical activity, four times a week. However, as Mike Sleap points out, this is inappropriate for younger children, who tend to be active in short bursts and do not have the attention span for sustained physical activity.
The Pre-School Learning Alliance says that the under-fives need opportunities to build, climb and balance. It recommends activities such as running, pushing and pulling, jumping, rolling, hopping, throwing and crawling.
Cynthia James, former chair of BAECE, feels pre-school children must have freedom. "Small children require fresh air and exercise. They need to be able to move freely around the classroom, to rest and play when they need to. Physical activity should be provided in accordance with children's needs and not those of the building and the staff."