|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
|Short- and long-term effects of low or restricted energy intakes on the activity of infants and children|
|5. Short- and long-term effects|
Physical activity is markedly reduced in malnourished children. VITERI (1973) used an animal model to demonstrate that this reduced activity contributed, by itself, to growth impairment. Weanling rats were fed either 50 or 73% of the food normally eaten by rats of the same age. When they were inactive, living in small metabolic cages, growth in length and weight gain were significantly less (p < 0.01) than in pair-fed animals who lived in larger cages and were forced to run in a revolving drum twice daily.
The negative effect of inactivity on the growth of malnourished animals and the positive effect of exercise can be reversed, as shown in another experiment with a cross-over design with rats fed 60% of the normal food intake VITERI and TORUN, 1981). Whether the animals were inactive from the beginning of the study or became inactive after an initial period of forced activity, growth rate decreased. Conversely, an increment in activity produced better growth in length and weight.
The positive role of activity was further confirmed in the course of the nutritional rehabilitation of malnourished 2- to 4-year-old children (TORUN et al., 1976, 1979). When a group of patients were encouraged to participate in games that involved running after a ball, walking up a slope, climbing stairs and rolling and tumbling, they grew more in length and lean body mass than a control group of patients who continued with the usual, limited activities customary in most nutritional rehabilitation centers. Based on individual weekly calibrations of heart rate to oxygen consumption and heart rate monitoring, mean energy expenditure during the daytime was calculated as 1.97 X BMR in the more active children, compared with 1.70 X BMR in the control group.
In a more recent study using a similar program of physical activity in a hospital for malnourished children in Guatemala, but with food intake ad libitum, preliminary results indicated that the more active patients reached normal weight-for-height earlier than their less active counterparts (URIZAR and TORUN, unpublished).
It has not been shown whether physical activity has similar effects on the growth of children with mild and moderate dietary energy deficiency, but there are no reasons to believe that they would differ in this respect from the more severly malnourished children. As to the question of "How important is big?", we can answer that larger muscle (protein) and energy (fat) reserves might give poor, underprivileged children better protection against a recurrence of protein-energy malnutrition. Furthermore, as discussed below, small body size can limit maximal work output.