The endocrine response and substrate utilization during exercise in children and adolescents

Blood glucose levels and performance in a sports cAMP for adolescents with type 1 diabetes mellitus: a field study

Background. Acute hypo- and hyperglycemia causes cognitive and psychomotor impairment in individuals with type 1 diabetes mellitus (T1DM) that may affect sports performance. Objective. To quantify the effect of concurrent and antecedent blood glucose concentrations on sports skills and cognitive performance in youth with T1DM attending a sports camp. Design/Methods. 28 youth (ages 6-17 years) attending a sports camp carried out multiple skill-based tests (tennis, basketball, or soccer skills) with glucose monitoring over 4 days. Glucose levels at the time of testing were categorized as (a) hypoglycemic (<3.6 mM); (b) within an acceptable glycemic range (3.6-13.9 mM); or (c) hyperglycemic (>13.9 mM). Results. Overall, sports performance skill was approximately 20% lower when glucose concentrations were hypoglycemic compared to either acceptable or hyperglycemic at the time of skill testing (P < .05). During Stroop testing, "reading" and "color recognition" also degraded during hypoglycemia, while "interference" scores improved (P < .05). Nocturnal hypoglycemia was present in 66% of subjects, lasting an average of 84 minutes, but this did not affect sports skill performance the following day. Conclusions. Mild hypoglycemia markedly reduces sports skill performance and cognition in young athletes with T1DM.

Group- and individual-level coincidence of the 'Fatmax' and lactate accumulation in adolescents

Fatmax and lactate increase above baseline (LIAB) were measured in 11 adolescent girls and 8 adolescent boys during incremental cycling. Fatmax was the exercise intensity at the point of maximal fat oxidation rate (MFO). The LIAB was the exercise intensity coincident with a sustained increase in blood (lactate) above an initial baseline. We defined the minimum important difference (MID) between the exercise intensity at Fatmax and LIAB as +/-8% of both peak VO2 and peak heart rate (HR). Systematic bias was examined via the mean difference between parameters and its uncertainty, with inference based on the disposition of the confidence interval to the MID. Individual-level agreement was the proportion of differences between Fatmax and LIAB falling within the MID. MFO was at 35 (6)% peak VO2 with LIAB at 39 (7)% peak VO2 Systematic bias was -3.8% of peak VO2 and -4.4% of peak HR. The estimated population proportion with between-variable agreement within +/-8% was 0.76 for both % peak VO2 and % peak HR. Within the tolerance limits of the MID, the mean bias is 'almost certainly not' important; similarly, there is good agreement between the two parameters at the individual level. We conclude that Fatmax and lactate increase above baseline coincide in adolescents.

Twelve weeks of moderate aerobic exercise without dietary intervention or weight loss does not affect 24-h energy expenditure in lean and obese adolescents

BACKGROUND

Exercise might have a persistent effect on energy expenditure and fat oxidation, resulting in increased fat loss. However, even without weight loss, exercise results in positive metabolic effects. The effect of an aerobic exercise program on 24-h total energy expenditure (TEE) and its components-basal (BEE), sleep (SEE), and awake sedentary (SEDEE) energy expenditure and substrate oxidation-has not been studied in lean and obese adolescents.

OBJECTIVE

The objective was to test the hypothesis that 24-h energy expenditure and fat oxidation increase in lean and obese adolescents after 12 wk of moderate aerobic exercise without dietary intervention and weight loss.

DESIGN

Twenty-eight postpubertal Hispanic adolescents (13 lean [mean +/- SE: age, 15.3 +/- 0.3 y; body mass index (BMI; in kg/m(2)), 20.2 +/- 0.7; body fat, 18.7 +/- 1.6%] and 15 obese [age, 15.6 +/- 0.3 y; BMI, 33.1 +/- 0.9; body fat, 38.1 +/- 1.4%]) completed a 12-wk aerobic exercise program (4 x 30 min/wk at > or =70% of VO(2 peak)) without weight loss. Energy expenditure and substrate oxidation were quantified by 24-h room calorimetry at baseline and postexercise.

RESULTS

This aerobic exercise program did not affect 24-h TEE, BEE, SEE, or SEDEE in lean or obese participants. In obese adolescents, respiratory quotient (RQ) and substrate oxidation also did not change. In lean adolescents, 24-h RQ and RQ during SEE decreased (both P < 0.01) and fat oxidation increased (P < 0.01).

CONCLUSIONS

A 12-wk aerobic exercise program did not increase TEE, BEE, SEE, or SEDEE in either lean or obese sedentary adolescents. Furthermore, 24-h fat oxidation did not change in the obese adolescents, whereas it increased in the lean adolescents.

Fat oxidation rate and the exercise intensity that elicits maximal fat oxidation decreases with pubertal status in young male subjects

The range of exercise intensities that elicit high fat oxidation rates (FOR) in youth and the influence of pubertal status on peak FOR are unknown. In a longitudinal design, we compared FOR over a range of exercise intensities in a small cohort of developing prepubertal male subjects. Five boys all at Tanner stage 1 (ages 11-12 yr) and nine men (ages 20-26 yr) underwent an incremental cycle ergometry test to volitional exhaustion. FOR curves were determined from indirect calorimetry during the final 30 s of each increment. The same protocol was duplicated annually in the boys as they progressed through puberty. The peak FOR was considerably higher (P<0.05) in boys at Tanner 1 (8.6+/-1.5 mg.kg lean body mass(-1).min(-1)) (mean+/-SD) compared with men (4.2+/-1.1 mg.kg lean body mass(-1).min(-1)). FOR dropped as boys developed through puberty (Tanner 2/3 peak rate=7.6+/-0.6 mg.kg lean body mass(-1).min(-1); Tanner 4 peak rate=5.4+/-1.8 mg.kg lean body mass(-1).min(-1), main effect of Tanner stage; P<0.05) to the levels found in men (not significant). The exercise intensity that elicited peak FOR was higher in the boys at Tanner 1 [56+/-6% peak aerobic power (VO2 peak)] than in men (31+/-4% VO2 peak) (P<0.001). This value tended to decrease by Tanner stage 4 (45+/-10% VO2 peak, main effect of Tanner stage; P=0.06). We conclude that, compared with men, prepubertal boys have higher relative FOR throughout a wide range of exercise intensities and that FOR drops as boys develop through puberty.