When a developing baby delivers that first kick inside the womb, it’s a moment of elation for Mom that’s hard to beat. For doctors, physical activity of the fetus in utero is so important that when a baby seems to stop moving, tests are performed to check on its health. As the due date approaches, the workout gets more intense in a space that is increasingly confining as the baby grows. If a fetus is unable to move a limb, just as with adults, muscles and bones develop abnormally. “Use it or lose it” operates across the lifespan. So, what is the effect of early physical activity on growth and development?
We’re only beginning to understand. Early-life exercise has not been studied scientifically in any depth. In one 1950s experiment, scientists compared the long-term effects of gentle handling versus no handling of newborn rats. They made two striking observations: Gently handled animals were more active than those who were not; they also gained weight more rapidly and grew significantly larger by 21 days old – roughly equivalent to mid-childhood in humans. The researchers hoped their work would “reveal clues for the treatment and care of human infants.”
Recently, interest in how physical activity alters babies’ growth and development has reached new heights, and there is growing recognition among biologists of “critical periods” of effect. Their studies suggest that abrupt changes in a growing child or its environment, such as disease or insufficient food, may influence the child both at that moment and over a lifetime. For example, we know that levels of physical activity in children can affect bone strength throughout their lives, and the window of opportunity for optimal, lifelong bone growth is only open for a short time.
Premature birth and childhood obesity also are linked by the increasing awareness that early-life events can influence normal development and increase lifetime risk for diseases such as diabetes or atherosclerosis.
Because of advances in medical science, more children survive premature birth. Traditional hospital procedure has been to minimize unnecessary energy expenditure, ensuring that all calories consumed are used for growth. Ironically, the otherwise healthy premature baby is swaddled and immobilized during the same time that, in the womb, he would dramatically increase his physical activity. Some scientists are challenging this approach, suggesting that premature babies might benefit from more robust physical activity. An increasing number of studies show that gentle manipulation of arms and legs in preterm babies leads to larger muscles, stronger bones and production of natural hormones that promote growth. Premature babies who are exercised gain weight more rapidly than those who are not, and weight is one factor for determining when they go home from the hospital. Nurses and physicians at UC Irvine are conducting the largest-ever study on the role of exercise in premature babies. If the assisted exercise program proves beneficial, it will change dramatically how premature infants are cared for.
Childhood obesity rates are high because low-cost, high-calorie foods are readily available and opportunities to run and play are not. But in some cases, the roots of overweight begin very early in life with natural patterns of infant physical activity. Some intriguing observations suggest that movement is important to normal development. For example, a baby’s laughter is accompanied by a delightful burst of wriggling arms and legs. This connection between happiness and physical activity continues throughout life, and is captured by the phrase “jump for joy.” Because our brains link emotional happiness with motor activity, imprinting along with environmental influences on healthy, full-term babies may also have a lifelong impact on their physical activity levels.
To better understand the link between imprinting and environmental effects, UCI researchers systematically interview mothers and fathers about their baby’s activities. One observation by a Chinese mother was particularly fascinating. In some parts of China, she said, infants are tightly swaddled early in life for a period of several months, but the swaddling is removed during the hot summer months. Later, when a child is seen to be particularly active, adults will remark, “Oh, she must be a summer baby!” – a baby who was allowed to exercise in what may be a “critical period” of development. This kind of observation might help us improve health throughout life by giving us information about what is optimal activity in the first months.
On Sept. 27, we awarded prizes to the winners of the Children at Play Photo Contest during the Festival of Children at South Coast Plaza in Costa Mesa. Those of us from UCI, CHOC and The Orange County Register were excited to meet some of the parents and young people among the hundreds who participated. We think it means that Orange County is a community that cares about its children and its future. We look forward to next year’s contest and introducing more new and useful information about how exercise influences health and disease in the growing child.