Cardiorespiratory coupling tightens with workload during graded exercise: A pilot study with adolescent athletes

Area of Science:

• Exercise Physiology
• Cardiorespiratory Physiology
• Autonomic Nervous System Function

Background:

• Cardiorespiratory coupling (CRC) signifies the coordination between cardiac and pulmonary systems.
• Understanding CRC dynamics during graded exercise is crucial for assessing physiological adaptation.
• Previous research has not fully elucidated how CRC changes with increasing exercise intensity in adolescent athletes.

Purpose of the Study:

• To investigate the real-time covariation between cardiac timing and pulmonary oxygen uptake (VO2) during graded exercise.
• To determine if cardiorespiratory coupling strengthens with increasing workload in adolescent athletes.
• To analyze changes in heart rate variability and VO2 fluctuations with exercise intensity.

Main Methods:

• Observational, within-subject analysis of the ACTES cycling dataset.
• Eighteen adolescent athletes performed cycling exercise at 50, 110, and 140 W.
• Beat-to-beat RR intervals and breath-by-breath VO2 were analyzed using ultra-short segments, joint symbolic dynamics (JSD), and cross-correlation (X-Corr).

Main Results:

• Mean RR intervals decreased and mean VO2 increased significantly with workload (p < 0.0001).
• Heart rate variability indices (SDRR, RMSSD) decreased, while VO2 variability indices showed mixed changes.
• Cross-correlation (X-Corr) increased, and JSD indices (CSE) decreased with workload, indicating tighter CRC (p ≤ 0.0014 for CSE).

Conclusions:

• Cardiorespiratory coupling becomes more pronounced with increased exercise workload in adolescent athletes.
• This strengthening of CRC aligns with reduced heart rate variability and suggests vagal withdrawal.
• The findings reflect adaptive reflex responses that enhance heart-lung integration during exertion.