Marginal malnutrition and reduced physical work capacity of migrant adolescent boys in Southern Brazil

We measured the effect of marginal malnutrition on physical work capacity of adolescent children of agricultural migrant workers in Southern Brazil. Nutritional status was evaluated using 24-h dietary recall. Body size was evaluated anthropometrically. Biochemical assessments were also made. Physical work capacity (PWC170) was assessed by measuring heart rate, blood lactic acid levels, and oxygen consumption during submaximal bicycle ergometer work. The same tests were also carried out on a comparable group of local well-to-do boys of the same age in the same community who served as controls. The dietary results suggest that adolescent boys of migrant families were marginally malnourished. Their physical growth and development were retarded by at least 1 yr. They had significantly lower reserves of body fat and less muscle mass when compared with controls. Their Hb levels were normal. At the submaximal work loads measured (0, 25, 50, 75 W) the migrant children exhibited similar oxygen consumption and gross exercise efficiency as the control children, but achieved this work at a higher percentage of their maximum work capacity as shown by significantly higher heart rates for the same oxygen consumption. Higher blood lactic acid levels in the migrant children suggest that the available muscle mass was under greater stress to accomplish the same task. PWC170 was reduced one-third in the migrant children (migrant 643 +/- 162 kpm/min, control 905 +/- 345 kpm/min; p less than 0.005). These differences were largely associated with weight (migrant 20.6 +/- 5.9 kpm/min; control 18.8 +/- 4.3 kpm/kg/min; p greater than 0.1). These observations suggest that marginal as well as severe malnutrition affect physical work capacity at levels low enough to affect growth and development.