Determinants of mechanical efficiency trajectories from childhood to adolescence: Findings from the QUALITY cohort

Abstract

Purpose: To estimate the shape and number of mechanical efficiency (ME) trajectories from childhood to adolescence; and verify whether ME trajectory membership can be predicted by sex, biological maturation, body weight, body composition and physical activity (PA) in childhood.

Methods: Data from QUALITY, an ongoing cohort study on the natural history of obesity, were used. Participants attended a baseline visit (8-10 years, n = 630) and follow-up visits two years (n = 564), and seven years (n = 377) later. ME was assessed by an incremental cycling test at 50w (ME_50w, %) and at VO_2peak (ME_VO2peak, %). Group-based trajectory analysis for ME and a logistic regression were performed.

Results: Mean age of the 454 participants (boys = 54%) was 9.7 ± 0.9 years at baseline. Two distinct ME_50w trajectories were identified and all tended to decrease. No distinct trajectories emerged for ME_VO2peak; average ME_VO2peak increased over time. Thus, the difference between ME_VO2peak (∆) at baseline and follow-up was calculated for correlation analysis. Trajectory groups were labeled "Low-Decreaser" and "High-Decreaser" (Reference) for ME_50w, describing the starting point and slope. High-Decreasers were mostly prepubertal girls, had lower body weight and fat free mass index, lower PA and lower VO_2peak at baseline (χ²or t-test, p < 0.05). Girls were less likely to be Low-Decreasers (OR = 0.56, 95%CI = 0.42-0.74), while having overweight/obesity predicted a greater likelihood of classification in the Low-Decreaser trajectory (OR = 2.38, 95%CI = 1.16-4.88). Those with higher PA were more likely to be Low-Decreasers (OR = 1.02, 95%CI = 1.01-1.04). Finally, concerning ME_VO2peak, sex, biological maturation, body weight, zBMI, fat free mass index, PA and VO_2peak were positively correlated with ∆ ME_VO2peak.

Conclusions: We found evidence that excess weight at baseline predicts low levels of ME in childhood and adolescence. Additionally, higher PA at baseline is not related to higher ME_50w levels. More research is needed to identify different approaches to explore this measure in transition to adulthood.

Keywords: Adolescents; Body composition; Children; Mechanical efficiency; Physical activity; Trajectories.