Growth hormone response to a standardised exercise test in relation to puberty and stature

Abstract

Growth hormone (GH) was measured before and 10 minutes after a standardised bicycle exercise test (duration 15 minutes) in 37 short children (group 1: mean (SD) age 12.8 (3.5) years; mean (SD) bone age 10.4 (3.6) years; mean (SD) height standard deviation score (SDS) -2.8 (0.7)), 16 tall children (group 2: mean age 12.9 (2.8) years; mean bone age 13.9 (1.4) years; mean height SDS 3.0 (0.8)), and 30 normal children (group 3: mean age 13.3 (3.2) years; mean bone age 12.8 (3.4) years; mean height SDS -0.4 (0.8)). Results of GH are expressed as mean (SEM). The pre-exercise GH was similar in the three groups (group 1, 8.0 (2.3) mU/l, group 2, 8.5 (2.5) mU/l, and group 3, 8.3 (2.3) mU/l). There was a significant rise in GH after exercise in all three groups. GH after exercise was higher in group 2 (35.1 (2.5) mU/l) compared with groups 1 and 3 (17.8 (3.0) and 20.8 (3.2) mU/l). Post-exercise GH was <10 mU/l in 29 children (34% total; 49% group 1, 6% group 2, and 34% group 3). There was a positive relation between post-exercise GH and both bone age and pubic hair stage. Multiple regression analysis revealed that relevant predictors of a rise in GH with exercise were different for the sexes in these children with varying stature: for boys, bone age and pubic hair stage; for girls, height and height SDS. All the tall girls were in puberty. No statistical relation was observed between post-exercise GH and cardiovascular response to exercise, time of day of exercise, time of eating before exercise, and plasma insulin or insulin to glucose ratio at time of exercise. We conclude that the GH response to the physiological stimulus of exercise is higher in puberty compared with childhood. Therefore, although children may be suspected of having GH deficiency after a failure of GH to increase after exercise, a non-response may be a normal finding in prepubertal children, independent of stature.