All variables approximated a normal distribution (skew < 3, kurtosis < |10|). Outliers (approximately 1.5% of all data points) were recoded to fall within three standard deviations of the mean [38
]. One hundred thirty-four adolescents participated. Descriptive information on demographic and anthropometric characteristics is provided in . Approximately 16% of adolescents (n = 16) endorsed elevated depressive symptoms (CDI total score ≥ 13). Those with elevated depressive symptoms did not differ from those without elevated depressive symptoms in age, sex, race, lean mass, percent fat mass, weight, height, BMI z
score or number of obesity-related health co-morbidities.
Demographic Characteristics of Adolescent Study Participants by Depressive Symptoms Status
One-hundred three adolescents met criteria for reaching VO2max on their cycle ergometry test. Of the 31 youth whose cycle tests did not meet validity criteria, approximately 96% did not achieve an oxygen plateau, 97% had a maximal heart rate < 185 beats per minutes, 90% did not endorse the criterion cut-off for perceived exertion, and 41% did not meet the respiratory exchange rate criterion. Compared to those who achieved a valid cycle test, adolescents who did not achieve a valid cycle test were more likely to be younger (p < .01),non-Hispanic Black (vs. non-Hispanic White; p < .05), and to have a greater BMI z score (p < .05). There were no significant differences between those with and without a valid cycle test on any other variable, including depressive symptoms, sex, lean mass, percent fat mass, weight, height, or number of obesity-related health co-morbidities.
The remaining sample was comprised of 103 obese adolescent girls (68%) and boys with an average age of 14.6 ± 1.4 years. Average VO2max was 1975.2 ± 349.6 mL/min and ranged from 1238 to 2894 mL/min. Maximal heart rate was similar among adolescents with and without elevated depressive symptoms (186.2 ± 13.6 beats/min vs. 188.8 ±11.7 beats/min, p = .43), as was respiratory exchange rate (1.17 ± .07 vs. 1.16 ± .06, p = .51). VO2max was positively correlated with age (r = .24, p < .01), lean mass (r = .64, p < .001), weight (r = .54, p < .001), and height (r = .42, p < .001). Also, boys displayed greater VO2max than girls (M ± SE 2154.9 ± 70.8 mL/min vs. 1890.5 ± 34.1 mL/min, p < .01).
Adjusting for age, sex, race, and lean mass, adolescents with elevated depressive symptoms displayed poorer VO2max than adolescents without elevated symptoms (p = .04; ). Depressive symptoms status accounted for 4% of the variance in VO2max (η2 = .04). In analyses examining depressive symptoms continuously, the association between total depressive symptoms and VO2max did not reach significance (β = −.11, p = .12), accounting for age, sex, race, and lean mass. Adjusting for the same covariates, there was a significant, inverse association between anhedonia and VO2max (p < .05), such that higher reports of anhedonia were related to poorer exercise performance (). Above and beyond the contribution of age, sex, race, and lean mass (R2 = .50, p < .001), anhedonia explained a unique 3% of the variance in VO2max (ΔR2 = .03, p = .016). The relationships between other continuous dimensions of depressive symptoms and VO2max did not reach statistical significance (ps = .06 to .81).
Figure 1 Adolescents with elevated depressive symptoms (CDI Total Score ≥ 13) displayed lower VO2max (mL/min) during maximal cycle ergometry testing than adolescents with low depressive symptoms (CDI < 13), adjusting for age (years), sex, race, (more ...)
Figure 2 Adolescents’ self-reported anhedonia was inversely associated with VO2max (mL/min) during maximal cycle ergometry testing, adjusting for age (years), sex, race, and lean mass (kg), β (standardized regression coefficient) = −.17, (more ...)
Exploratory analyses tested sex as a potential moderator of the relationship between depressive symptoms and VO2max. The only significant effect was an interaction of sex by negative mood (p = .026). Negative mood scale score was associated with poorer VO2max among boys only (β= −.22, p = .024), but not among girls (β= .06, p = .56). Sex did not act as a significant moderator in any other model.