Impact of Circadian and Ultradian Rhythms on Metabolic, Cardiovascular, and Athletic Performance Outcomes among Elite Endurance Athletes

Rationale:
The biological rhythms, including circadian and ultradian rhythms, are endogenous oscillations of biological processes that are driven by internal molecular clocks (Liu et al., 2024). However, there is limited research examining how these rhythms interact with training time-of-day, sleep–wake patterns, and recovery dynamics in elite African endurance runners, despite their global athletic dominance.
This project addresses this gap by combining field-based wearable monitoring with a controlled intervention to explore how chronobiological factors, such as training time-of-day and chronotype, affect training quality, cardiovascular regulation, metabolic markers, and overall athletic performance. The findings aim to inform time-of-day–specific training strategies and enhance performance optimization models grounded in sport science and chronophysiology.

Objective:
The general objective of this study is to characterize training load, intensity distribution, physiological responses, mechanical performance, and circadian influences on training quality in elite Ethiopian endurance runners using longitudinal wearable-derived data and coach perspectives..

Specific Objectives:
• To longitudinally quantify training load, intensity, and volume characteristics of routine endurance running sessions using device-derived metrics in elite Ethiopian endurance runners.

To examine training characteristics, planning practices, and intensity distribution philosophies among Ethiopian elite endurance coaches.

To describe physiological and performance profiles of elite Ethiopian endurance runners during routine training sessions.

To investigate the relationship between training intensity and mechanical performance indicators in elite endurance runners.

To determine whether morningness–eveningness preference moderates the effect of training session timing on training quality in elite runners.

To analyze diurnal variations in training intensity distribution and external-load mechanical indicators using wearable monitoring in elite Ethiopian endurance athletes.

• To analyse the interaction between chronotype, training time (morning vs. afternoon), cardiovascular function and athletic performance outcomes.
• To determine the effect of training quality on elite athletes performance adaptations (i.e., VO₂max, lactate threshold, and HRV).
• To examine the relationship between prior-night recovery (sleep and HRV) with next-day training and race performance during competition periods.
• To confirm the combined predictive value of chronotype, circadian rhythm markers, and training quality for elite athletes' performance and recovery outcomes.

Study Design:
This research employs a mixed-method exploratory–confirmatory design composed of two complementary phases:

1. Exploratory Observational Phase:
• Design: Prospective Observational longitudinal cohort study
• Duration: 14 weeks of real-world field monitoring.
• Participants: 14 elite Ethiopian endurance athletes (Tier 4 & Tier 5) and 10 Coaches
• Data: Continuous wearable-based HR, HRV (RMSSD), sleep, and training load metrics (via COROS, Tymewear, and other validated devices).
• Analysis: Descriptive, correlational, chronotype and rhythm analysis (Cosinor and FFT) to identify individual circadian and ultradian patterns.

2. Confirmatory Experimental Phase (RCT):
• Design: crossover randomized controlled trial comparing morning versus afternoon training conditions.
• Each athlete (14)completes both conditions with 10 – 14 day washouts period.
• Outcomes: VO₂max, HRV, RPE, lactate threshold, and recovery markers.
• Analysis: Linear mixed-effects modeling, repeated-measures ANOVA, and hierarchical testing for rhythm–performance interactions.
• All sessions are supervised by certified coaches, physicians, and physiologists to ensure protocol fidelity and participant safety.

Ethical Approval:
Ethical clearance for this study has been granted by the Institutional Ethical Review Board (IERB) of Addis Ababa University, College of Natural and Computational Science (Approval Reference: EDRE/04/2017/25, dated 10 November 2025).
All participants will provide written informed consent (and parental consent/assent for minors aged 15–17). Data confidentiality, anonymity, and secure storage procedures are maintained in accordance with AAU and international ethical standards.

Expected Outputs:
• Three to four peer-reviewed journal publications derived from the exploratory and confirmatory phases.
• Practical guidelines for training quality and chronobiology-informed training periodization in elite endurance athletes.
• Contributions to the understanding of chronotype and training time-of-day influences on human performance within African athletic populations.

Key Words:
circadian rhythms, ultradian rhythms, heart rate variability, speed, intensity, endurance, performance, chronotype, pace, cadence, training districution, training load, training quality, training intensity distribution, wearable technology, training time-of-day, Ethiopia