SERUM INSULIN-LIKE-GROWTH-FACTOR-I AND PHYSICAL PERFORMANCE IN PREPUBERTAL BOLIVIAN GIRLS OF A HIGH AND LOW SOCIOECONOMIC-STATUS

The aim of the study was to determine if a decrease in serum insulin-l ike growth factor I (Igf-I) levels under marginal malnutrition is resp onsible for the lower physical performance of girls of a low socio-eco nomic status (LSES). Girls were selected after physical examination (T anner's stage 1) and anthropometric measurements (height, body mass or mb, body mass index or BMI = m(b) height(2)). Lean body mass m(b,l) w as measured after skinfold thickness determination; serum IGF-I, by ra dioimmunoassay; maximal O-2 consumption, ((V) over dotO(2max)), direct ly during incremental exercise up to exhaustion; and maximal aerobic p ower ((W)(max)), using the force-velocity test. LSES girls (n = 31) ha d been malnourished in the past and, currently, were suffering from ma rginal malnutrition: they were smaller (135.2 +/- 5.5 vs 146.1 +/- 4.3 cm), lighter (31.7 +/- 3.9 vs 37.6 +/- 5.0 kg), exhibited a lower m(b ,l) (24.2 +/- 2.5 vs 27.5 +/- 3.0 kg) but same BMI compared with HSES (high socio-economic status) girls (n 32). Igf-I levels (27.7 +/- 7.9 vs 34.1 +/- 6.5 nmol . l(-1)), (V) over dotO(2max) (45.26+/- 4.72 vs 5 0.74 +/- 6.02 ml . min(-1) . kg(-1) LBM) and (W) over dot(max) (6.00 /- 1.15 vs 8.70 +/- 1.53 W . kg(-1) m(b,l) were lower in LSES girls. M oreover, the differences in every parameter were not the consequence o f the younger age (10.8 +/- 0.9 vs 11.2 +/- 0.6 years) of the LSES gir ls. Our results provide evidence that the lower (W over dot(max) of un dernourished prepubertal girls was partly the consequence of alteratio ns in muscle function at the qualitative level, as a result of a decre ase in Igf-I levels. Conversely, under normal nutritional conditions, anthropometric characteristics only are explicatory factors for physic al performances.