Aerobic Function and Muscle Deoxygenation Dynamics during Ramp Exercise in Children

Area of Science:

• Pediatric Exercise Physiology
• Muscle Oxygenation Dynamics
• Cardiorespiratory Fitness

Background:

• Peak oxygen uptake (peak V˙O2) is lower in girls compared to boys.
• Understanding the physiological factors contributing to this sex difference is crucial for optimizing training and health outcomes in children.
• Muscle deoxygenation dynamics during exercise may play a role in cardiorespiratory fitness differences.

Purpose of the Study:

• To investigate sex differences in deoxyhemoglobin ([HHb]) response dynamics during ramp incremental exercise in children.
• To determine if altered muscle oxygenation dynamics contribute to the lower peak V˙O2 observed in girls.
• To explore the relationship between muscle oxygenation parameters and peak V˙O2.

Main Methods:

• Fifty-two children (31 boys, aged 9.9 ± 0.6 years) underwent ramp incremental exercise on a cycle ergometer.
• Pulmonary gas exchange and muscle oxygenation (using deoxyhemoglobin, [HHb]) were measured continuously.
• Analysis focused on [HHb] response dynamics, including the c/d parameter and plateau, relative to work rate and V˙O2.

Main Results:

• Girls exhibited an earlier increase in muscle [HHb] when expressed against absolute work rate and V˙O2, indicated by lower c/d and plateau values.
• No sex differences in [HHb] response dynamics were found when expressed against relative work rate or V˙O2.
• Muscle [HHb] dynamics, particularly the plateau, significantly correlated with and contributed to the variance in peak V˙O2, independent of fat-free mass and body fatness.

Conclusions:

• Sex-specific changes in muscle oxygen extraction dynamics during incremental exercise partially explain the sex difference in peak V˙O2 in 9- to 10-year-old children.
• These findings highlight the importance of considering muscle oxygenation in understanding cardiorespiratory fitness disparities between sexes in children.
• The results suggest that differences in how muscles extract oxygen during exercise contribute to lower aerobic capacity in girls.